Strutt, 2002;Tree etal.,2002;KleinandMlodzik,2005;Strutt area [reviews withanemphasison excellent anddetailedreviews have recentlybeenpublishedinthis to cover thePCPfield inacomprehensive mannerbecausemany the activity ofasubsetPCPcomponents.We have notattempted suggestive, but stillincomplete, evidence forPCPsignalingor PCP anddiscussseveral developmental processesinwhichthereis interesting. Inthisreview, wehighlightrecentwork onvertebrate in vertebrates, have madethestudy of vertebrate PCPuniquely together withtheexistence ofanumberdistinctPCPcomponents invertebrates inanatomy, tissuetypesandmorphogeneticprocesses, system. However, thenumerousdifferences betweenvertebrates and served asthesourceformany ofthecomponents andconceptsinthis field owes alarge debttoits role isrevealed inever morediverse developmental processes. name ‘tissuepolarity’ mightultimatelyprove moreappropriateasits Gubb andGarcia-Bellido’s original andsomewhat moregeneral Although thisphenomenonisnow commonlyreferredtoasPCP, tissue movements andpatternsinbothinvertebrates andvertebrates. a complex systemofdevelopmental regulation thatgoverns celland patterns. Thegenesthatthey studiedarenow known tobeplayersin of ageneticallydefined systemdedicatedtocoordinatingthese represented aconceptualdepartureinthatitsuggestedtheexistence respect tothebodyaxes, but GubbandGarcia-Bellido’s work appreciated thepreciseorientationofcuticularstructureswith e-mails: [email protected]; [email protected] School ofMedicine,Baltimore, MD21205,USA. 1 in small setofgenescontrolsthepolaritycuticularhairsandbristles Gubb andGarcia-Bellido(GubbGarcia-Bellido,1982)thata planar cellpolarity(PCP)began 25yearsagowiththerealization by The geneticandmoleculardissectionofwhatisnow referredtoas Introduction Drosophila similarities, aswelldifferences, existbetweenPCPin Studies inmice,frogsandzebrafishhaverevealedthat movements requiredforneuraltubeclosureandtubulogenesis. left-right asymmetry, aswellbetweentheorientedcell connections existbetweenthePCP-basedorientingsystemand hair follicles.Recentworkhasshownthatintriguing vestibular sensoryneurons,andmulticellularstructures,suchas subcellular structures,suchashairbundlesinauditoryand to thebodyaxes.Interestingly, thesystemactsonboth global andlocalsignalstoorientdiversestructureswithrespect vertebrates. CurrentevidencesuggeststhatPCPintegratesboth pathway anditsroleingeneratingspatialpatterns This reviewfocusesonthetissue/planarcellpolarity(PCP) Yanshu Wang new questions Tissue/planar cellpolarityinvertebrates:newinsightsand (2007)doi:10.1242/dev.02772 Development 134,647-658 and Department ofMolecularBiologyandGenetics, Howard HughesMedical Institute As isoftenthecaseindevelopmental biology, thevertebrate PCP 2 Drosophila Departments ofNeuroscience andOphthalmology, JohnsHopkinsUniversity and vertebrates. . Morphologistsandembryologistshadlong 1 and Jeremy Nathans Drosophila Drosophila counterpart, whichhas 1,2 PCP (Adler, 2002; surrounding tissue eitherturntoward oraway from theclonalpatch backgrounds. Inthesestudies, bristlesandhairswithinthe surrounding tissuethatiseither WToroneofvarious mutant and loss-of-functioncloneshave beenstudiedinthecontext of abdominal epithelium,awidevariety ofPCPgeneover-expression cells thatresidedistaltothepatch ofmutanttissue.Inthe of homozygous example, inthewing,domineeringnon-autonomycausedbyaclone misorientation isonlyobserved ononesideofthemutanttissue.For phenotype (Vinson andAdler, 1987).Inmany cases,the cells adjacenttoacloneofmutantexhibit amisoriented referred toas‘domineeringnon-autonomy’ inwhichWTepithelial and localorientation. existence ofmechanisticallydistinctsystemsforcontrollingglobal structures inthecontext ofglobaldisorderstronglysuggeststhe below, thispropensity forlocalorderamongneighboringpolar (Chae etal.,1999;Usui1999)].Asdiscussedmorefully also known as In PCP in paragraphs thatfollow wecanconvey someofthisexcitement. that addressinterestingunansweredquestions.We hopethatinthe have focusedonthoseareasthatwethinkarethemostexciting and mechanisms ofplanarpolarityinplants(Grebe,2004)].Instead,we Montcouquiol etal.,2006a);areview onthevery different (Wallingford etal.,2002;Barrow, 2006;Karneretal., Strutt, 2005);reviews onvarious aspectsofvertebrate PCP Rubin, 1998)]and impressionist painting,inspiringthemutantnames create whorlsandwaves thatresemblethebrushstrokes ofan 1D), leadingtolarge-scale patternsinwhichmany hundredsofhairs tend toberoughlyalignedwiththeirimmediateneighbors(seeFig. cause acompleterandomizationofhairorientation.Rather, hairs et al.,2005).Inthewing,mutationsinPCPgenesgenerallydonot packing ofthewingepithelialcellsareunderPCPcontrol(Classen orientation ofthewinghairsandhexagonal shape and regular distally-directed actin-filled protrusion(awinghair).Boththe epithelium ofhexagonal cells,eachofwhichelaborates asingle zone. that individual ommatidiaofthe‘wrong’ chiralityarefoundin each the spatialsegregation ofommatidialchirality islost,withtheresult Fig. 1A,B).InPCPmutants,theommatidiaarevariably orientedand segregated intotwo mirrorimagezonesbyatransverse equator(see In thewild-type(WT)eye, ommatidiaofdiffering chiralityare as defined bytheasymmetricpackingofeightphotoreceptors. Moreover, eachommatidiumexhibits oneoftwo possiblechiralities, each ommatidiumispreciselyorientedinanearlycrystallinelattice. in moststudiesofPCPproteinlocalization.Inthecompoundeye, studying PCPphenotypes(Fig.1),andthewinghasalsobeenused The The surface ofthewingiscovered byanearlycrystalline Drosophila Drosophila Drosophila , theeye andwinghave beenthefavored tissuesfor Strabismus frizzled starry night wing hasalsorevealed aninterestingfeature mutant cellsgenerallyaffects onlythoseWT or Stbm [ stan (Taylor etal.,1998;Wolff and ; alsoknown as REVIEW Van Gogh flamingo Drosophila [ or Vang 647 fmi ;

DEVELOPMENT of PCPproteins inthe proximal (P)anddistal(D);anteriorisup.( orientations globally, butsubstantialalignmentlocally. Arrow indicates pointing winghairs.( vertebrates) toactivate, inamannerthatisstill poorlydefined, aJun complexes. cooperative andasymmetricassemblyofcell-surface signaling the asymmetricpropagationofasignalingmoleculeand/or the tissue (Casaletal.,2006).Thisasymmetryismostlikely toreflect clonal patchandtheanteriororposteriorlocationofsurrounding in amannerthatischaracteristicofthemutantgenotypeeach Stan/Fmi, Starrynight/Flamingo. Dishevelled; Fz,Frizzled;Pk,Prickle;Vang/Stbm, Van Gogh/Strabismus; Dgo,Diego;Ds,Dachsous;Dsh, (Jenny andMlodzik,2006). respectively. A-Dreproduced withpermissionfrom JennyandMlodzik accumulation atproximal ordistalfacescodedinred orgreen, hexagonal wingepithelialcellsare shown,withPCPprotein 2002; KleinandMlodzik,2005;StruttStrutt,2005).Fouradjacent rotation. ( Vang of theequatorseparatingtwoterritoriesdiffering chirality. Inthe (black orred arrows forthedifferent chiralities;green fornonchiral)and are schematicsofthechiralityandorientationeachommatidium or blackcircular structures withineachommatidium).Therightpanels arrangement ofindividualphotoreceptor rhabdomeres (thecentralgrey ( subcellular localizationofPCPproteins inwingepithelialcells. Fig. 1.PCPphenotypeinthe 648 recruits theadaptorproteinDishevelled (Dshin Wnt signalingpathway inwhich acell-surface Frizzled(Fz)receptor principal PCPsignalingpathway appearstobethe‘noncanonical’ A ) AWTeye.( There areroughlytencorePCP genesin mutant eye,theommatidiashowdefectsinbothchiralityand REVIEW C ) WTwingshowingthenearlyparallelalignmentofdistally B ) Vang D Drosophila ) mutant eye.Theleftpanelsshowthe Vang mutant wingshowingaberranthair Drosophila wing epithelium(Adler, 2002;Strutt, E ) Thesubcellularlocalization eye andwing, Drosophila Drosophila ; Dvlin . The Wnt signaling(Simons etal.,2005);andproteins, suchasthec-Jun appear tocontrolthebalancebetween canonicalandnoncanonical faces ofthecell(Djianeet al.,2005);,suchasinversin, that localization ofPCPproteinstothe apicaledgeofoneorbothlateral this groupare:proteins,such asPatj, thatareinvolved inthe proteins essentialforPCPbut notsolelydevoted toit.Included in discussed below. revealing ofhow PCPcomponentsfunction,several ofthemare Since thesenon-planarandnon-epithelialprocessesarepotentially cortical sliceculturesleadstolossofdendrites(Shimaetal.,2004). vertebrate homologsof mutations, asituationobserved for might maskadefectassociatedwithsingle-,loss-of-function Casal etal.,2006).We note,however, thatredundancy amongWnts implicate any WntinPCPsignaling(KleinandMlodzik, 2005; Wnts, theonlyknown Fzligandsin parallel ratherthaninseries(Casaletal.,2006). Drosophila Mlodzik, 2005).However, recentgeneticmosaicexperiments inthe al., 2004;Venema etal.,2004;StruttandStrutt,2005;Klein al., 2002;Maet2003;UemuraandShimada,Lawrence et Adler, 1993;Adleretal.,1997;Adler, 2002;Strutt,Yang et intracellular adaptorlike ,Diego (Dgo)(Fig. 1E)(Wong and cell-surface complexes composedofFz,Vang, Dsh,Stanand an which isthensensedandpropagatedbytheasymmetricassemblyof complex protein,Four-jointed (Fj),setupaglobalpolaritysignal, Dachsous (Ds)andFat (Ft),togetherwithatransmembraneGolgi uncertain. Oneattractive modelpositsthattwo atypicalcadherins, signal thatcommunicatespolaritybetweenneighboringcellsremain that communicatestheorientationofbodyaxes andthelocal signaling betweencells,atpresenttheidentitiesofglobalsignal first identified inzebrafish (Slusarskietal.,1997).With respectto G-protein Galpha-O(Katanaev etal.,2005),asignaling pathway which Fz-dependentPCPsignalingalsoutilizestheheterotrimeric Genetic gain-andloss-of-functionexperiments supportamodelin et al.,1997;Boutros1998;Wallingford andHabas,2006). kinase-Rac-Rho pathway thatcontrolscytoskeletal dynamics(Strutt Kimura etal.,2006),andRNAi knockdown of nervous system(Gaoetal.,2000;Lee2003;Senti etal.,2003; morphologies insensoryneuronstheembryonicperipheral aberrant pathfinding byphotoreceptoraxonsanddefective dendritic the mutationofcorePCPgene tissue patterningbut whichdonotinvolve epithelia.For example, both vertebrates andinvertebrates thatinvolve PCPgenes incellor (Figs 2and3).Attheedgeofthisdefinition aresomeprocessesin in innerearsensorycells,andhairfollicleorientationtheskin extension, neuraltubeclosure,eyelid closure,hairbundle orientation developmental processesthatmeetthesecriteriaareconvergent phenotype ofthe involves oneormoreofthe corePCPgenes(asdefined bythePCP process thataffects cellpolaritywithinanepithelialplaneand entirely clear. Oneroughoperational definition isthatPCPany In vertebrates, thedefinition ofwhatconstitutes aPCPprocessisnot PCP processes andcomponentsinvertebrates possibility thatoneormorenon-WntFzligandsmightregulate PCP. (Xu etal.,2004)suggeststhatthefield shouldbeopentothe recent identification ofanon-Wntligand(Norrin)forvertebrate Fz4 Carthew, 1998;Bhanotetal.,1999;ChenandStruhl,1999).The context ofembryonicpatterning(Bhat,1998;Kennerdell and In additiontothecorePCPproteins, thereisawidercircleof Ironically, boththelossoffunctionandover-expression of abdomen argue thatthesetwo systemsmayfunctionin Drosophila stan , inratorganotypic cerebellar and homolog). Atpresent,the frizzled stan Drosophila in Development 134(4) Drosophila and Celsr2 , have failed to frizzled2 , oneofthree leads to in the

DEVELOPMENT dorsal surfaceofthe tube (craniorrhachischisis)ina are indicatedbywhitearrows. ( staining oftheanteriortwo-thirds oftheeye;edgeseyelids 18. ( Fig. 2.Mouseplanarcellpolarityphenotypes. includes 2006; Wang etal.,2006b). machinery mayalsoplayasupportingroleinPCP(Shimadaetal., population –suggeststhatcomponentsofthevesicular transport proteins –perhapsservingasareservoir fortheplasmamembrane that thereareintracellular(mostlikely vesicular) pools ofsomePCP dynamics. Therecentobservation inboth RhoA (Rho1–Flybase)andRac1,thatcontrolcytoskeletal N-terminal kinase(JNK)(Basket –Flybase)andthesmallGTPases Development 134(4) with permissionfrom Wang etal.(Wang etal.,2006b). of outerhaircells; OHC3,outerrow ofouter haircells.Reproduced inner haircells;OHC1,row ofouterhaircells;OHC2,centralrow Bottom, diagramsofhairbundleorientations foreachimage.IHC, (red) andkinociliaare labeledwithanti-acetylatedtubulin(green). Corti flatmount.Top, actin-richstereocilia are labeledwithphalloidin hair bundleorientationatE18ina beyond therightedgeofeachimage. ( and distal(right).Thebasesofthecentraldigitsare immediately when mutatedsinglyorincombinationwithoneanother, gives PCP- homologous toacorePCPgenein al listsvertebrate genesthatplayaroleinPCP. Thislist Table 1 B ) Openeyelidsina Vangl2 , Dvl1 Fz6 , –/– Dvl2 Fz3 paw atpostnatalday(P)8.Proximal (left) –/– , ;Fz6 Fz3 C Celsr1 ) Hairfollicleorientationdefectsonthe –/– –/– Vangl2 ;Fz6 Drosophila fetus atE18,shownbyphalloidin , D Fz3 –/– ) Defectsininnerearsensory mutant ( fetus atembryonicday(E) Drosophila and . Eachofthesegenes, Fz6 ( Lp/Lp A , eachofwhichis ) Fullyopenneural ), organof and mammals al., 2003;Luet2004).Alsoincludedaregenessuchas both aloneandincombinationwithotherPCPgenes(Murdochet generate compellingPCPphenotypeswhenmutatedinvertebrates, Wang etal.(Wang etal., 2006b). kinocilium atthe left edge.PanelAisreproduced withpermissionfrom (a) andvestibularsystem(b).Theapical faceisatthetopandsingle cristae. ( of haircellsintheorganCortiand adiscintheutricle,sacculeand bundles). Inthisview, thestereocilia formaVshapeontheapicalface lies adjacenttoagroup of stereocila (structures filledwithactin and three ofouter(OHC)hair cells.Inc,eachkinocilium(blackcircle) Organ ofCortihaircellsare arrangedinfourrows: one ofinner(IHC) sensory hairbundlesinsertintotheoverlyingtectorialmembrane. calcium carbonatecrystals,theotoliths;andinorganofCorti, sensory hairbundlesinsertintoagelatinousstructure filledwith gelatinous structure calledthecupula;inutricleandsaccule, sensory hairbundlesontheapicalfaceofeachcellinsertintoa Forge, 1999).Intheampullaofsemicircular canals,thetipsof than towards eachotheracross theequator(Denman-Johnson and utricle, exceptthatitshairbundlesfaceawayfrom eachotherrather structure inthecochlea).Thesaccule(notshown)closelyresembles the each semicircular canal),utricle,andorganofCorti(thesensory bundles. Lefttoright:crista(thesensoryepitheliumintheampulla of the apicalfaceofsensoryhaircellsandarrangement sensory haircells.(c)Face-onviewsoftheseepithelia,showing Cross-sections through themaintypesofsensoryepithelia,showing (b) ear showingthelocationsofcross-sectional viewsbeneath. sensory structures. (a)Thestructures ofthebonylabyrinthinner Scribble like phenotypesinvertebrates. Thetablealsoincludes genessuchas Fig. 3.Themammalianinnerear. evidence from A B B b c Cupula ( ) Schematicofindividualhaircells from theauditorysystem canals circular Semi- Scrb1 mul til OrganofCorti Utricle Ampulla ab a Crista etblrsse Auditory system Vestibular system Auditory haircell Kinocilium ) [ Drosophila Scribbled Stereocilia Otoliths Nucleus ( Scrib regarding aroleinPCP, but which Ampulla ( )] and A ) Locationandarchitecture of Kinocilium Vestibular haircell OHCs Ptk7 membrane Tectorial Cochlea , forwhichthereisno Stereocilia Nucleus REVIEW IHC inturned 649

DEVELOPMENT Widerborst Vangl2 Scribble Ptk7 Price etal.,2006); Prickle Inversin Inturned Fz6 Fz3 Fuzzy Dvl3 Dvl2 Dvl1 Celsr3 Celsr2 Celsr1 Bbs6 Bbs4 ( Widerborst † arborization neuronmigration growth,guidance patterning closure extension closure Bbs1 haircellorientation Vertebrate gene Table 1.PCPgenesandPCP-related processes invertebratedevelopment 650 al., 2005); Simons etal.,2005); et al.,2006a;Wang etal.,2006b;Wada etal.,2006); References: interpreted cautiously. , oneormore ofthe listed characteristicsmaynothavebeenexaminedorinsufficient detailtodeterminewheth another PCPmutation;D*,defectiveonlyinadoublemutantcombination(i.e.redundancy betweengenefamilymembers);–,notr Phenotypes associatedwithPCPgenesinvertebrates:D,defective;(D),defective,buteitherlowpenetranceorobservedasan Habas, 2006).In mice,lossof (Wallingford etal.,2000;Wallingford etal.,2002;Wallingford and domains, whichin negative Dishevelled variant that lackseithertheDEPorPDZ several PCP proteins,forexample byoverexpressing adominant- (Heisenberg etal.,2000)andin 2002), disrupted inzebrafish bymutationof et al.,2000;Wallingford etal.,2002;Goto2005).CEcanbe extracellular matrix(ECM)fibrils, inparticularfibronectin (Keller lateral faces ofthesecellsandbytheorganized depositionof cells, movements thataredirectedbylamellipodia onthemedialand defects (Coppetal.,2003). 1000 live births,makingitoneofthemost commoncongenital fuse theneuraltubeinitsentiretyoccursatafrequency of1in ultimately fusetocreatetheneuraltube.Inhumans,afailure to dorsal margins ofthetwo walls ofthisU-shapedstructure The elongatedneuralplatedevelops acentral groove, andthe narrowing oftheembryo,referredtoasconvergent extension (CE). frogs andfish, theprocessbegins with an elongationand fascinated embryologistsforover acentury(Wilson, 1925).In most ancientofvertebrate embryologicalprocesses,and they have Neurulation anditsassociatedtissuemovements areamongthe Oriented cellmovementsanddivisions role inPCPorPCP-like processes. are includedthateitherbyhomologyorfunctionlikely toplaya extension phenotype(Park etal.,2006).Other, miscellaneousgenes expression studiesinfrogsorfish embryos, to give aconvergent Drosophila Implicated inciliaryfunction. in CE reflectsthemedialmigrationandintercalationofmesodermal ) and † † † † - 1 REVIEW prickle fuzzy Vangl2 † (Hannus etal.,2002). Bbs1 and whichhave beenfound,byinhibition or over- , ( Bbs4 (Greene etal.,1998;Kibar etal.,2001;Murdoch etal.,2001;Bingham2002;JessenMontcouquiol fy Dvl1 ), whichareconsideredtobePCPeffector genesin (Veeman etal.,2003),or Prickle-1 uioy etblr erltb ovretEei arAo idri Dendritic Hindbrain Axon Hair Eyelid Convergent Neuraltube Auditory, vestibular , , Bbs6 Dvl2 , Drosophila (Ross etal.,2005); Dvl3 (Carreira-Barbosa etal.,2003; Veeman etal.,2003); *D *(* – – – D – D D – (D*) (D*) D* D* D* D* D* D* *D *––––– D – – – – – – – – D* D* D* D* D* D* DDDD––D–DDD–––D–DD–D–––– DD–D––(D)–D–(D)–––––DD(D)–––––D––––––– ––D–––D– ––D––––– ––D–D–––––D–––––––D––––– –D*–––––––––D––––––––DD –– (Hamblet etal.,2002;Rosso2005;Wang etal.,2005;Wang, J.etal.,2006); Vangl2 Xenopus Dsh areessentialforPCP vangl2 (Greene etal.,1998; Kibaret Celsr1 by interferingwithany of Fz6 ( (Curtin etal.,2003); trilobite (Guo etal.,2004;Wang etal.,2006b;Wang etal.,2006c); wnt11 ) (Jessenetal., ( silberblick Celsr2 Ptk7 (Shima etal.,2004;Kimura2006;Wada etal.,2006); ) (Lu etal.,2004); Fig. 3A),andthisshapechangefails tooccurin development oftheorgan ofCortiinthemammaliancochlea(see epithelial sheets. tube closure,involves a medial convergence ofapairflanking closure normallyoccursataboutE16inthemouseand,like neural PCP mutantsalsoshow aneyelid closuredefect(Fig.2B).Eyelid open neuraltubeandashortenedembryo.Itisinterestingthatmany Genome Informatics)(Wang etal.,2006b),allleadtoacompletely correlation betweenvertebrate and Fz signalingmakes itdifficult toestablishaclearone-to-one Thorpe etal.,1997).Althoughtheevolutionary divergence ofWnt- mitotic spindlesinseveral blastomeres(Rocheleau etal.,1997; Mutations in polarity ofcleavage planesduringearlycelldivisions in genetic disruptionofWnt-Fzsignalingcamefromstudies the (Wang, J.etal.,2006). indicating thatthisprocessdoesnotinvolve orientedcelldivision movements occuraftersensorineuralprecursors have exited mitosis, Wang etal.,2005;Wang etal.,2006b).Intheorgan ofCorti,CE-like all alsohave neuraltubeclosuredefects(Montcouquioletal.,2003; Dvl1;Dvl2 J. etal.,2006),orofboth Dishevelled homologs( (Lu etal.,2004),orthesimultaneouslossoftwo ofthethree al., 2001;Murdochet2001), normal gastrulating zebrafish embryos, dorsalepiblastcellsinall imaging zebrafish that ubiquitouslyexpress histoneH2B-GFP. In (Gong etal.,2004)have extended thiswork tovertebrates by some elementsofPCPsignaling (Park etal.,2004).Gongal. it seemslikely thatthepathway defined bythe A narrowing andlengtheninganalogoustoCEalsooccursduring One oftheearliestdescriptionsphenotypicconsequence of double-mutants, andin Scribble mom-2 (Murdoch etal.,2003;Montcouquiol etal.,2003;Wada et (a Wntgene)or Inturned Dvl1 Fuzzy Fz3 (Park etal.,2006); and increase intheseverityof phenotypeof (Park etal.,2006); er itisnormal;thus,a–entryshouldbe and Celsr1 Dvl2 eported asabnormal.Forsomeofthese Fz3;Fz6 C. elegans Fz6 ) (Hambletetal.,2002;Wang, mom-5 (Curtin etal.,2003),or ( Fzd3 2003;Torban etal.,2004); Celsr3 Fz3 double-mutants, which Inversin Development 134(4) (a Fzgene)misorient (Wang etal.,2002;Wang mom signaling pathways, and (Tisser etal.,2005; (Tisser Vangl2 (Otto etal.,2003; Fzd6 genes includes C. elegans – Mouse mutants, Ptk7 .

DEVELOPMENT to radialmigration. underlying neuroepitheliumwith aconcomitantswitchfromcaudal function leadstotheintercalation ofthenVIImotorneuronsinto to bemaintainthesecellsat the pialsurface. LossofPCPgene in promotingthecaudaltrajectory ofthenVIImotorneuronsappears et al.,2005;Wada etal.,2006).Theprincipalroleof the PCPsystem include cell-nonautonomouscomponents (Jessenetal.,2002;Wada that eachofthesegenespromotesmigrationbymechanisms that migration (Wada etal., 2006).Geneticmosaicexperiments show chemical mutagenesisscreensforimpairednVIImotorneuron Wada etal.,2006)].The Jessen etal.,2002;Carreira-Barbosa2003;Wada etal.,2005; [ ( atr1bt ( factor-1 beta known as by mutationsinthezebrafish genes et al.,2000).nVIImotorneuronmigrationisimpairedorabolished selectively inthissubpopulationofhindbrain neurons(Higashijima that pharmacologicallyblockingcelldivision inthe underlies theneuraltubeclosuredefectcamefromobservation striking demonstrationthatthefailure toreintegrate thesecells center oftheU-shaped,andincompletelyclosed,neuralfold.A accumulation ofapicaldaughtercellsfromrecentmitosesinthe Ciruna etal.observed thatlossof neuroepithelium fromwhichthey hadbeentransiently extruded. required forthereintegration ofnewly postmitoticcellsintothe function ofPCPinzebrafish neuraltubeclosure.Instead,PCPis shown thatcoordinatingpolarizedcelldivision isnottheprincipal on zebrafish gastrulation,Cirunaetal.(Cirunaal.,2006)have be determined. extent towhichPCPsignalingplaysaroleinthisprocess remainsto mice] andfoundclearevidence supportingboth hypotheses. The [polycystic kidney disease( controls andinratmousemodelsofcystic kidney disease examined individual tubules fromthedeveloping kidney inWT daughter cells(Germino,2005).Fischeretal.(Fischeral.,2006) transverse, ratherthanoflongitudinal,orientationspairs the tubule, andthatcyst formationarisesfromanexcess of preferential displacementofpairsdaughtercellsalongtheaxis hypothesized thatdeveloping tubule elongationrequiresthe developing renaltubules (Fischeretal.,2006).Ithasbeen recently comefromthestudyofmitoticspindleorientationin orchestrated byPCP. and tissuegrowth maybedriven byorientedcelldivisions These observations suggestthat,insomecontexts, tissuemovements morpholino oligonucleotidesthatblockthesynthesisofVangl2. expression ofdominant-negative Dvlproteinsorbyinjectionof and thisalignmentdependsonPCPsignalingasitisdisruptedbythe layers tendtoaligntheircelldivisions alongtheanimal-vegetal axis, Development 134(4) zebrafish thatexpress an (Chandrasekhar etal.,1997).Thismigrationcanbevisualizedin their birthplaceinrhombomerefourtosix (which formtheseventh cranialnerve, nVII)migratecaudallyfrom is foundinthezebrafish hindbrainwherefacial motorneurons trilobite inhibitors didnotrescuetheCEphenotypealsocausedby without celldivision therearenoextruded cells.Bycontrast,mitotic late ingastrulationrestoresneuraltubeclosure,presumablybecause fz3a ord In contrasttotheobservations ofGongetal.(Gongal.,2004) New insightsintothecontroloforientedcell division have The clearestexample ofPCPcontrolorientedcellmovement ; oneoffour / olt ; oneoftwo mutation. pk1 ), Hnf-1 scribble1 stan ; fz3 Tcf2 homologs inzebrafish (Binghametal.,2002; homologs inzebrafish), and / landlocked islet1-GFP fz3a – MouseGenomeInformatics)-deficient Pkd and mutantratsandhepatocyte nuclear ) celsr2 vangl2 ( Vangl2 transgene, whichisexpressed scrb1 genes wereidentified in ( / llk trilobite ( trilobite ), frizzled3a trilobite ), celsr2 prickle1 ) leadstoan / off-limits / off-road mutant (also members: asseen inTable 1,many mammalianPCPgenes are reflect theparticipationofadditional andpartiallyredundantfamily only mildouterhaircelldefects. Someofthesedifferences may mutants have severe orientationdefectsoftheinnerhair cellswith al., 2006b).Incontrasttoboth of thesepatterns, hair cellsandmilderdefectsin all otherrows ofhaircells(Wang et to causesevere misorientationdefectsintheoutermostrow of outer 2003), whereasthesame of outerhaircellsseverely misorientated (Montcouquioletal., row ofinnerhaircellsaswelltheoutermosttwo ofthethreerows in onestudy, also dependonthegeneticbackground.Asanexample ofthelatter, and thesubsetsofhaircellsaffected vary betweenmutants,andmay et al.,2005;Wang etal., 2006b).Interestingly, theseverity ofdefects Genome Informatics)double-knockout mice(Luetal.,2004; Wang ( simultaneously reportedthatmutationsin 2003) andMontcouquioletal.(Montcouquiolal., epithelia (Eaton,1997).Sixyearslater, Curtinetal.(Curtinal., stereociliary hairbundles withintheplaneofinnerearsensory shortest stereociliafurthestfromthekinocilium(seeFig.3B). manner withthelongeststereociliaclosesttokinociliumand stereocilia vary inlengthandarearrangedaprecisestep-wise kinocilium atonesideofthecluster. Inallsensoryhairbundles, the utricule, sacculeandcristae)arearrangedinadensecluster, withthe (Fig. 3).Thestereociliaofvestibular haircells (i.e.thoseinthe shape ofachevron, withthekinociliumlocatedatapex oftheV face on,thestereociliaofcochlearhaircellsarearrangedin channels; anddeflectionstoeithersidehave no effect. Whenviewed cation channels;deflectionaway fromthekinociliumcloses bundle deflectiontoward thekinocilium opensplasmamembrane directional selectivity onthemechanicalresponseofcell:hair to theplaneofepithelium.Hairbundle orientationconfersa structure, thesensoryhairbundle, ispreciselyorientedwithrespect true ,thekinocilium(Fig.3B).Thismechanosensory on itsapicalface asetofactin-filled stereociliaadjacenttoasingle In particular, eachprimarysensoryneuron,thehaircell,elaborates 2004; Fritzschetal.,Romand2006). 2003; Kelley, 2003;WrightandMansour, 2003;BaraldandKelley, Hedgehog, Notch,Neurotrophin,BMP, WntandFGFsystems(Gao, shown toplayaroleinitsdevelopment, includingtheretinoicacid, developmental signalingsystemsknown invertebrates have been inner ear, itisperhapsnotsurprisingthatmostoftheprincipal gyroscopes calledsemicircularcanals.Given thecomplexities ofthe by sensingtheinertialdisplacementoffluidinthreemicroscopic crystals (otoliths);andthecristae,whichdetectangularacceleration sensing theinertialdisplacementofextracellular calcium-carbonate cochlea; theutricleandsaccule,whichdetectlinearaccelerationby shearing motionofthestructureswithincentralcavity ofthe detects airbornevibrations(i.e.sound)following its conversion toa sensory epitheliaexist intheinnerear:organ ofCorti,which arranged withextraordinary precision(Fig.3A).Threetypesof neurons, specializedextracellular deposits,andaxonsareall bone, vasculature, fluid-filled chambers,supportingcells,sensory The vertebrate innerearisanarchitecturaltour-de-force inwhich Inner eardevelopment in orientation defectsintheorgan ofCortihave sincebeendescribed precisely thisphenotypeintheorgan ofCorti.Hairbundle and Lp Nine yearsago,EatonproposedthatPCPsignalingorients The structuralprecisionoftheinnerearisreiteratedsubcellularly. Ptk7 ) mousemutant], Celsr1 knockout and (in the Vangl2 Scribble spin cycle homozygotes werereportedtohave thesingle Dvl1;Dvl2 Vangl2 [in the and allele was reportedinanotherstudy Circletail and crash Fz3;Fz6 Vangl2 mouse mutants)cause ( Crc Fz3;Fz6 REVIEW ) mousemutant], ( [in the Fzd6 – Mouse Looptail double- 651

DEVELOPMENT vestibular system,lossof closure (Wang etal.,2006b).Inthefirst analysesofPCPinthe inner eardevelopment andarelargely redundantinneuraltube unaffected. Inthe neuronal proliferationandmigrationintheforebrainappeartobe al., 2005;Priceet2006;Bovolenta etal.,2006). Inbothmutants, et al.,2002;Wang etal.,2006a;Lyuksyutova etal.,2003;Tissir et stall ratherthanturnrostrallyaftermidlinecrossing(Fig.4)(Wang the thalamusandcortex, andcausesspinalcordsensory axonsto of eitherthesegeneseliminatesthemajoraxontractsthatconnect Celsr3 phenotypes identified todateisseeninmicethatlackeither these processesareatleastpartiallyrelated. epithelial andneuronalpatterningsuggeststhatatamolecularlevel discovery thatPCPcomponentsfunctioninthecontext ofboth epithelial cellssharethesamePCPmechanisms.However, the in thisreview isnotnecessarilymeanttoimplythatneuronsand The inclusionofasectiononaxonguidanceanddendriticpatterning The growth andguidanceofaxonsdendrites and theeffect ofPCPgenemutationonproteinlocalization. determining thesubcellularlocalizationofvertebrate PCPproteins below, theinnerearhasalsoprovided ausefulsystemfor implicating Wntligandsintheorientationprocess.Asdescribed soluble Wnt-bindingproteinsleadstomisorientedhairbundles, et al.,2003).Inthisexplant system,theapplicationofWnt7aor during whichtimehairbundles refine theirorientations(Dabdoub the organ ofCorticanbeculturedinvitroforatleastoneweek, cell resolution.Moreover, thedeveloping sensoryepitheliumfrom mammalian PCPphenotypecanbequantitatively scoredatsingle- studying vertebrate PCP. Atpresent,itistheonlyplacewherea the innerearsensoryepitheliumoffers apowerful systemfor al., 2006b;Wang, etal.,2006b). bundle orientationinboththeutricleandcristae(Montcouquiolet together withthe growing commissural axonscrossthemidline.Althoughthesedata, abundance alongthe spinal cordatmidgestationthetimewhen promotes rostralturning,show arostral-caudalgradientof turning. Intriguingly, transcriptsencodingWnt4,aWnt that Lyuksyutva etal.observed thatseveral Wntsstimulaterostral cell aggregates cultured adjacenttothespinalcordexplant, diffusion. Intestingaseriesofcandidatefactors producedbyCOS orienting factor was beinglostfromtheexplant bylongitudinal explants arecutintonarrow transverse strips,suggestingthatan rostral turninginembryonicspinalcordexplants islostifthe axons, Lyuksyutova etal.(Lyuksyutova etal.,2003)observed that that they functiontogetherinacommonaxonguidancepathway. their observed inthesetwo mutants,andtheknown interactionsbetween but fail toexit thethalamus.Thenearidentityofphenotypes By contrast,inbothmutantsthalamicaxonsextend andfasciculate to asimilaroutcomefor eventually degenerate (Wang etal.,2006a).Preliminarydatapoint bundles would normallyform,but theseaxonsfail toextend andthey intermediate zone,thecorticallayerinwhichcorticothalamicaxon YFP shows thatprojectionneuronssendtheiraxonsintothe using genetically-directedcelllabelingwithalkalinephosphataseor with thisidea, members ofsmall,highlyhomologousgenefamilies. Consistent 652 In mammals,oneofthemostdramaticaxongrowth andguidance Aside fromitsimportanceinthecontext ofhearingandbalance, In asearchforfactors thatpromoterostralturningofcommissural Drosophila , whicharehomologsofcorePCPgenesin REVIEW Fz3 homologs inthecontext ofPCP, argues strongly Fz3 Fz3 and –/– –/– Fz6 Celsr3 rostral-turning defect, suggestthatWnt4 cortex, ananalysisofcellmorphologies Vangl2 appear tobecompletelyredundantin –/– cortical axons(Priceetal.,2006). was foundtorandomizehair Drosophila Fz3 . Loss or the proximaland distalfaces ofepithelial cells.Itistemptingto homophilic clusteringand,inthe inhibition islost.Whenexpressed inculturedcells,Stanmediates commissural axonsinE11WTand staining ofhorizontalsectionsthrough E15WTand panel BiscourtesyofDrsLibingZhouandAndre Goffinet. reproduced withpermissionfrom Wang etal.(Wang et al.,2002)and the midline.A,Anterior/rostral; P, posterior/caudal.PanelAis beyond theleftedgeofeachimage.Theverticalwhitelineindicates ‘open book’preparation). DiIwasplacedincommissuralcellbodies spinal cord hasbeenopenedatthedorsalmidlineandflattened(an bundles inanotherwisenormal-appearing shows acompleteabsenceofthalamocorticalandcorticothalamicfiber failure ofrostralby turning location ofthesefibersisindicatedbyanarrowhead. ( surface oftheembryo.In arbors fromcontralateraldaneurons, therebyefficiently tilingthe dorsal midline,they avoid growing intoregions thatareoccupiedby when dendritesofdendriticarborization (da)neuronsreachthe et al.,2004;Kimura2006).IntheWT mammalian homologCelsr2,respectively (Gao etal.,2000;Shima the axis viaitsinteractionwithMIG-1(aFz)(Pan etal.,2006). 20 (aWnt)appearstorepelaxongrowth alongtheanterior-posterior guidance hascomefromrecentgeneticstudiesin However, independentsupportforthisgeneralmechanismofaxon direct biochemicalevidence thatthesetwo proteinsinteract. promotes growth coneturningbyactivating Fz3,thereisasyetno Fz3 Fig. 4.Axongrowth andguidancedefectsinthedeveloping As notedabove, thegrowth andmaintenanceofdendritesinboth –/– Drosophila and Celsr3 and mammaliannervous systemsinvolve Stanorits –/– central nervoussystem. Celsr stan –/– Celsr3 axons aftermidlinecrossing. The Drosophila mutants, thisdendriticgrowth –/– Fz3 mouse spinalcords showsa –/– ( wing, localizestoboth A Development 134(4) forebrain; thenormal Drosophila ) Anti-neurofilament Fz3 C. elegans B –/– ) DiItracingof mouse brains embryo, : EGL-

DEVELOPMENT follicle iscomposedofhundredscellsandseparatedfrom single actin-richprotrusion(thehair),whereaseachmammalianhair is oneofscale:in between mammalianhairfolliclesand orientation withrespecttothebody’s axes. Aprincipaldifference therefore eachfollicleanditsassociatedhairhasadefined surface. Hairfolliclesmake anacuteanglewiththeskin,and the regular andlocallyparallelarrangementofhairsover thebody oriented patterningofhairsandbristlesonthe The mammalianPCPphenomenonthatmostcloselyresemblesthe separate globalandlocalcontrol systems Hair follicleorientationandhairpatterning: follicle orientation atP8).InbothWTand reoriented toproduce spatialdomainswithimperfectlocalorder. Additionalreorientation continuesoverthenextseveraldays range from ~–45to+45degrees, adistributionthatnarrows byP4.(C,D) anterior-posterior axis(setatzero degrees andcorresponding tothecentralpoint alongeachaxis).(A,B)WTfolliclesatP0 angles ofeachhairfollicleshaft(the region closesttotheskinsurface)andbase(theregion furthestfrom theskinsurface Fig. 5.Hairfollicleorientations onthebackofWTand development, culturedhippocampalneuronsfrom Also consistentwitharoleforPCP-like signalingindendritic components inthecontext ofbothPCPanddendritedevelopment. contain Stanmaysignaldirectlyorlocalizesignaling speculate thathomo-orheterophilicadhesioncomplexes that Development 134(4) Mouse GenomeInformatics)and pathway componentsglycogensynthasekinase-3(Gsk-3;Gsk3a– neurons isinsensitive tothecotransfectionofcanonicalWnt arborization thatisproducedbythetransfectionofDvlintoWT with theirWTcounterparts,andtheincreaseingrowth and show adecreaseindendriticgrowth andarborizationascompared chloride or6-bromoindirubin-3 pharmacological inhibitionofGsk-3bytreatmentwithlithium Reproduced withpermissionfrom Wang etal.(Wang etal.,2006c). Drosophila , eachwingepithelialcellmakes a Ј -oxime (Rossoetal.,2005). Drosophila Fz6 ␤ –/– -catenin, ortothe skin, thedistribution ofshaftanglestightensmore thanthatofbulbangles. Scale bar, 400 Drosophila hairs andbristles Dvl1 Fz6 cuticle is –/– –/– mice mice atP0andP4. Fz6 of itsneighbors.Thisregular arrangementisdefective in orientation ofeachfolliclecloselymatchestheaverage orientation neighboring folliclesbytensofcelldiameters.Ingeneral,the are almostperfectlyparallel.Asnotedabove, two-stage modelshave initially imperfectfollicleorientationstoproducethat follicles. InWTmice,thelocalmechanismefficiently refines signal toproducenomorethanaroughalignmentofimmature globally, andasecondthatactslaterlocally. distinct orientingsystems,onethatactsearlyindevelopment and system thatalignsneighboringfollicles.Thus,thereappeartobetwo The subsequentreorientationisorchestratedbyaFz6-independent the globalorientationofhairfollicleswithrespecttobodyaxes. data indicatethatFz6normallyfunctionsearlyindevelopment toset reorienting inresponsetosurroundingcuesamatterofdays.The follicles, despitetheirlarge size,possessanunexpected plasticity, (Wang etal.,2006c).Thisanalysisalsoshows thatmammalianhair initially misorientedorrandomlyorientedhairfollicles(Fig.5) patterns arisebyaprocessofself-organization fromafield of and earlypostnataldevelopment shows thatin (Figs 1and2)(Guoetal.,2004). whorls andtufts,eachcomprisingdozenstohundredsofelements globally disorganized but locallyordered,giving risetowaves, orientations aredefective in in thesamedistinctive mannerinwhichbristleandwinghair –/– The existence ofalocalrefinement mechanism permitstheglobal A recentanalysisofWTand follicles atP0haverandomorientations, whichbyP4havepartially ( A-D ) Posterioristotheright.Thescatter plotsshowthe Drosophila Fz6 –/– skin duringlateembryonic PCP mutants:thepatternis ) withrespect tothe have orientationsthat (seeFig.2Cfor Fz6 REVIEW –/– mutants, hair Fz6 ␮ –/– m. mice 653

DEVELOPMENT Fig. 6.Atwo-dimensionallatticemodelof ones defined bythe independent processesobserved in although itisnotclearwhethertheFz-dependentandFz- also beenproposedinthecontext ofPCPsignalingin 654 is appliediteratively, and,witheachiteration,itsubtlybiases and alocalconsensus‘rule’ (Fig.6)(Wang etal.,2006c).Therule modeled withatwo-dimensional latticeofuniformlyspacedvectors the progressive refinement ofhairfollicleorientationscanbe probabilities foralloftheindividual spins.Bothferromagnetism and in theformofexternal magneticfield, biasesthealignment favor thealignmentofadjacentelectronspins,andaglobalsignal, both localandglobaleffects: localquantummechanical interactions patterning ofelectronspinsinaferromagnet.AsPCP, thereare PCP patterningbearsastrongconceptualresemblancetothe 2003), isconsistentwithatwo-stage process. mammals andbirds(CotancheCorwin,1991;Dabdoubetal., orientations withintheinnerear, aphenomenonobserved inboth For example, theprogressive refinement ofsensoryhairbundle may alsoexist inthecontext ofotherPCPprocessesinvertebrates. with the downstream torefine thatorientation,would appeartobeatodds global orientation,andaFz,Vang, DshandStansystemacts general ideathataDs,FtandFjsystemactsupstreamtosetup Wang etal.(Wang etal., 2006c). bar, asshowninthekeytoright. Reproduced withpermissionfrom orientation isrepresented bytheangleandcolorofcorresponding and 100iterationsofthelocalconsensus algorithm.Eachvector set ofrandomlyorientedvectors, and thelatticeisshownafter10,20 isa circles ofsurrounding latticepoints.Thestartingconfiguration(0) magnitude. Thisnumberofneighbors corresponds totwoconcentric its 18closestneighborsafterthat sum hasbeenscaledto2%ofits vector’s orientationbecomesmodifiedbyaddingtoitthevectorsumof by repeated applicationofanupdatingrule,whichspecifiesthateach triangles. Aftertheinitialvectororientationsare set,thelatticedevelops length vectorplacedatoneoftheverticesalatticeequilateral orientation development. As first notedbyLewis andDavies (Lewis andDavies, 2002), REVIEW Fz6 –/– hair patterningphenotype.Two-stage mechanisms Fz6 –/– Each hairfollicleisrepresented byaunit- hair folliclephenotype.Indeed,the Drosophila Fz6 are analogoustothe –/– hair follicle Drosophila , disruption of its cellularanchor, thebasalbody(Ansley etal.,2003).Targeted common featurethattheencodedproteinslocalizetociliumor 2006). Bbsgenesarestructurallydiverse but many sharethe degeneration andhearingloss(Bisgrove andYost, 2006;Davis etal., dysfunction, cystic renaldisease,progressive photoreceptor pleiotropic manifestationsincludingobesity, polydactyly, endocrine syndrome (BBS),ageneticallyheterogeneoushumandisorderwith between PCPandciliahascomefromthestudyofBardet-Beidl have thusfar onlybeenfoundonsubsetsofneurons.Onelink the cell.Bycontrast,in cilium), whichistypicallylocatedinthecenterofapicalface of epithelial cellspossessasinglenonmotilecilium(theprimary 2006; SinglaandReiter, 2006).Invertebrates, many, ifnotall, structure and/orfunction(Bisgrove andYost, 2006;Davis etal., that several genesthataffect vertebrate PCPalsoaffect ciliary emerged betweenPCPandnonmotilecilabasedontheobservation A fascinating, but stillpoorlyunderstood,connectionhasrecently PCP andcilia dominate anotherwiserandomlyorientedpopulationoffollicles. the abilityofasmallinitialbiasinvector orientationtorapidly WT patternsintoadjacent accretion ofhairpatternsduringdevelopment, thespreadoforiented attributes ofhairfolliclepatterning,includingthegrowth by neighbors’ orientations.Thissimplelatticemodelcapturesthekey vector’s orientationinfavor ofthemostrecentaverage ofits identification ofthemouse effects onPCPmayextend beyond their rolesinciliarystructure. knocked down inzebrafish (Yen etal.,2006)–andthereforetheir defects inmelanosometransportthatoccurwhenBbsgenesare context ofcytoskeletal regulation – asindicated,forexample, by some, andperhapsmost,Bbsproteinsmayalsofunctioninthewider phenotypes, includingafailure ofembryonicCE.We notethat oligonucleotide knockdown of alleles interactgeneticallywith cephalic neuraltube(exencephaly). Moreover, both bundles (Rossetal.,2005),and14%of Informatics) inmiceleadstomisorientationofinnerearsensoryhair protein Diego. large adaptor-like proteinwithhomologytothe Drosophila experiments with (Germino, 2005). and, withit,misregulated tubule growth andcyst formation signaling andlower inversin activity favoring canonicalsignaling with higherinversin activity favoring noncanonical(i.e.PCP) the balancebetweencanonicalandnoncanonicalWntsignaling, for CE(Simonsetal.,2005).Thedatasuggestthatinversin controls accelerates itsdegradation, andin 2004; Nurnberger, 2004).Intransfectedcells,inversin bindsDvland spindle poles(Morgan etal., 2002; Watanabe etal.,2003;Eley etal., basal bodies,primaryciliaand,duringmetaphaseandanaphase, the localization ofinversin iscomplex anddynamic,but includesthe (Otto etal.,2003;Bisgrove andYost, 2006).Thesubcellular failure inbothmiceandhumans(nephronophthisistype2, NPHP2) Invs (Mochizuki etal.,1998;Morgan etal.,1998;Okada1999). apparently theresultofaciliarydefectinembryonicnode transgene insertionevent thatproduceda A secondlinkbetweenPCPandciliahascomefromthe The mostrecentlinkbetween PCPandciliacomesfrom mutations alsocausecystic renaltubules andprogressive renal PCP genes Invs Bbs1 Xenopus was discovered astheserendipitoustarget ofa , Bbs4 fuzzy Drosophila Fz6 inversin and embryos inwhichhomologs of the or –/– inturned Bbs6 skin (inWT: Bbs4 Xenopus and ( Invs Bbs4 Vangl2 ( in zebrafish leadstoPCP C. elegans Mkks situs inversus were unexpectedly found ) gene,whichencodesa –/– embryos itisrequired Development 134(4) Fz6 , andmorpholino mice displayanopen – MouseGenome –/– Drosophila , nonmotilecilia Bbs1 chimeras), and phenotype, and Bbs6 PCP

DEVELOPMENT localization. (C,D)OrganofCortifrom aWT: from Wang et al.(Wang etal.,2006b). intracellular accumulationonlyinWT cells.Reproduced withpermission ofC,showingFz6punctate (A). (E)Anenlargementoftheright corner deeper planethantheapicaledge ofthecells,where Fz6accumulates epithelium. Fig. 7.Fz3andFz6localizationinmouseinnerearsensory remains obscure. role inPCP. Atpresent,themechanisticbasisofthisconnection that ciliaorcytoskeletal structuresthataffect ciliaplayanimportant 2006). underlying actinskeleton isofabnormallylow density(Park etal., morphants in Consistent withthishypothesis,ciliain Inturned andFuzzyplayaroleinciliarystructureorfunction. Anderson, 2006;Huangfuand2005)suggeststhat (IFTs) impairsHedgehogsignaling(reviewed byHuangfuand that lossofvarious intraflagellar(i.e.ciliary)transport proteins discovery, inanunbiasedchemicalmutagenesisscreenthemouse, to berequiredforHedgehogsignaling(Park etal.,2006).Theearlier Development 134(4) expression variesamong (asterisks). Phalloidin(blue)stainsactin bundles. bundles. ( lateral facesthatorientperpendiculartotheaxisofsensoryhair the apicalfaceofsensoryneurons. Fz6localizespreferentially on on theactin-richcuticularplate(phalloidin,red), whichcoversmuchof sensory hairbundlekinociliaorienttotheright,asindicatedbyhole visualize nuclear immunostained withanti-Fz6(red) andanti- expressed insupportingcellsandsensoryneurons. In the OHC3, outerrow ofOHCs.( cells; OHC1,innerrow ofouterHCs;OHC2,centralrow ofouterHCs; at P0.Actinbundlesare stainedwithphalloidin(red). IHC,innerhair The evidence summarizedintheprecedingparagraphs indicates C-E ( ) WT: A ) ImmunolocalizationofFz3(green) intheorganofCorti Xenopus ␤ -galactosidase encodedby Fz6 –/– mouse embryochimerasandFz6protein Fz6 are shortandoftenmisshapen,the –/– B ) Inthevestibularsystem,Fz6(green) is cells. Thenuclei(D)are present ina ␤ Fz6 Fz6 -galactosidase (green) to –/– ␤ –/– Inturned -galactosidase embryo chimera ( lacZ knock-in) cells Fz3 and –/– crista, Fuzzy for Fz3orFz6 reveals numerouspunctateimmunoreactive inspection ofconfocalimages sensoryepthitheliaimmunostained of theFz3andFz6proteins(Wang etal.,2006b). mutant isassociatedwithlittle or nochangeinthetotalabundance complete absenceofFz3and Fz6 atthecellsurface ina with theproteinatcellsurface. Consistentwiththismodel,a pool ofFz(andperhapsotherPCPproteins)thatisinequilibrium immunoreactivity exhibits analogousbehavior inthe immunostaining atthecellsurface isincreasedrelative toWT. Fz3 inner ear, theasymmetriclocalizationofFz6,whereWTand E) (Wang etal.,2006b).SinceFz3isfullyredundantwithFz6inthe lost ina the surface ofhaircellsandsupportingcells,thislocalizationis EGFP expressed fromaBAC transgenelocalizesasymmetricallyat papilla (Davies etal.,2005).Inthemouseorgan ofCorti,Dvl2- cells andsupportinginthesensoryepitheliumofbasilar In thechicken innerear, Celsr1localizesasymmetricallyinbothhair accumulate attheapicaledgeoflateralfaces ofepithelialcells. observations toemerge fromthestudyofPCPin One ofthemoststrikingandmechanisticallysignificant PCP protein localization inner ear, ispresumedtohave thesamesubcellularlocalization. chimeric sensoryepitheliaandperformsthesamefunctionin the Fz3, whichhasthesameimmunostainingpatternasFz6innon- localization occurswithrespecttothepolarityofepithelium. supporting cellsandhaircells,thatthepolarityof Fz6 tissue. Thisanalysisshows thatFz6accumulatesapicallyinboth cells interface, takes placeinthecontext ofphenotypically normal of ear. Theseobservations areconsistentwiththegeneticredundancy distinction byimmunostainingWT: of Fz6localizationintheinnerear, ithasbeenpossibletomake this one ortheother(orboth)surfaces ofneighboringcells.Inthecase distinction tobemadebetweenthelocalizationofPCPproteins with respecttotheglobalaxisofepithelium. appears tobehighlysensitive totheorientationofcell’s sides 7A,B) (Wang etal.,2006b).TheassemblyofPCPproteincomplexes epithelia, andthislocalizationisalsolostinthe surface ofhaircellsandsupportinginallinnerearsensory 2006). Similarly, Fz3andFz6colocalizeasymmetricallyatthe only justbeginning. Asin surface oftheadjacentcell(intrans). surface ofthesamecell(i.e.incis),orwithPCPproteinsat proteins interactwitheachothereitherdirectlyorindirectlyatthe have provided evidence thatseveral ofthegeneticallydefined PCP of overexpressed PCPproteinsandproteinfragments,thesestudies 2002; KleinandMlodzik,2005).Together withtheco-precipitation and ofmutatingvarious PCPgenes(reviewed byAdler, 2002;Strutt, protein localizationofjuxtaposingclonesmutantandWTcells faces (seeFig.1E).Furtherexperiments examined theeffect onPCP are under-represented ontheremaining(i.e.anteriorandposterior) localizes tobothproximalanddistalfaces; andalloftheseproteins each cell;Dsh,Dgo,FtandFzlocalizetothedistalface; Stan wings, Ds,Prickle(Pk),andVang localizetotheproximalface of Shimada etal.,2001;Strutt,2001).Ingeneticallymosaicpupal faces ofR3andR4photoreceptors(Usuietal.,1999;Axelrod, 2001; or distalfaces ofwingepithelialcellsandonasubsetthelateral several PCPproteinsareasymmetricallydistributed ontheproximal What formmighttheintracellular poolsofFztake? Careful Interestingly, intheinnerearsof The spatialresolutionoflightmicroscopy doesnotpermita Analogous studiesofPCPproteinlocalizationinvertebrates are Fz3 and Vangl2 Fz6 , andthey suggesttheexistence ofanintracellular ( Lp ) mutant(Wang etal.,2005;Wang, J.etal., Drosophila Fz3 Fz6 –/– –/– , PCPproteincomplexes mice, theintensityofFz6 chimeric tissue(Fig.7C- Vangl2 Drosophila REVIEW mutant (Fig. Fz6 –/– Vangl2 Fz6 is that inner 655 –/–

DEVELOPMENT Axelrod, J.D. Ansley, S.J.,Badano,J.L.,Blacque,O.E.,Hill,Hoskins,B.Leitch,C.C., Barrow, J.R. Barald, K.F. andKelley, M.W. Bhanot, P., Fish,M.,Jemison,J.A.,Nusse,R.,Nathans,andCadigan,K.M. Adler, P. N.,Krasnow, R.E.andLiu,J. Bhat, K.M. Carreira-Barbosa, F., Concha,M.L.,Takeuchi, M., Ueno,N.,Wilson,S.W. Boutros, M.,Paricio,N.,Strutt,D.I.andMlodzik,M. Bisgrove, B.W. andYost, H.J. Adler, P. N. References Institute. The authorsacknowledgethesupportofHoward HughesMedical they areabsentintissuefromwhichthecorresponding cannot beascribedtobackgroundstainingorotherartefacts because structures, presumablyvesicles, withinthecytoplasm. Thesepuncta 656 Bingham, S.,Higashijima,Okamoto,H.andChandrasekhar, A. Bovolenta, P., Rodriguez, J. andEsteve,P. 2006), anditseemsplausibleinboth of Fzhasrecentlybeendescribedin been deleted,asshown inFig.7C-E. Polarized vesicular transport this anexciting areaofinquiryformany yearstocome. defects inPCP?Addressingtheseandotherquestionsshouldmake processes utilizePCPsignaling?Whichhumandiseasesarisefrom function inaxonguidance?Whichothertissuesordevelopmental but nototherplasmamembraneregions? How doFz3andCelsr3 complexes? How arethesecomplexes selectively localizedtosome received? Whatarethecompositionsofcell-surface PCPsignaling the globalorientingsignal?How arelocalorientingsignalssentand currently many morequestionsthananswers.Whatis the natureof The studyofvertebrate PCPisstillinitsinfancy, andthereare Conclusions 2006b) suggestthatFz3andVangl2 colocalize. the mouseinnerearMontcouquioletal.(Montcouquiolal., Vang localizetooppositesidesofwingepithelialcells,whereasin between been interpretedtoimplythatafundamentaldifference exists interaction foreach(Montcouquioletal.,2006b).Thesedatahave Vangl2 andFz3expressed intransfectedcellsindicateadirect Binding experiments betweenVangl2 andScribblebetween along thecircumferenceofcell(Montcouquioletal.,2006b). cytosolic proteinwithmultiplePDZdomains)localizesuniformly pattern very muchlike thatofFz3,whereasScribble (alarge components atthecellsurface. the trafficking ofvesicular poolsmayregulate theabundance ofPCP 628-633. Frizzled planarcellpolaritysignaling. dysfunction isalikelycauseofpleiotropic Bardet-Biedl syndrome. Kim, J.C.,Ross,A.J.,Eichers,E.R.,Teslovich, T. M.etal. Biol. that havehigherFrizzledlevelstowards cellsthathavelowerFrizzledlevels. in innereardevelopment. during Drosophila embryonic development. (1999). FrizzledandDfrizzled-2functionasredundant receptors forWingless ofpolarityinembryonictissues. patterns 525-535. and neuronal migrationinzebrafish. and Tada, M. disorders. branchiomotor neurons. The Zebrafishtrilobitegeneisessentialfortangentialmigrationof Cell wingless signalingandhavesimilarrequirements towinglessinneurogenesis. signalling inaxonguidance. wingless signaling. activates JNKanddiscriminatesbetween JNKpathwaysinplanarpolarityand The immunolocalizationofVangl2 intheinnerearshows a 95 7 , 940-949. REVIEW , 1027-1036. Drosophila (2002). PlanarsignalingandmorphogenesisinDrosophila. Development (1998). frizzledand2playapartiallyredundant role in (2006). Wnt/PCPsignaling:averitablepolarstarinestablishing (2001). UnipolarmembraneassociationofDishevelledmediates (2003). Prickle1regulates cellmovementsduringgastrulation Cell 94 and mammalianPCP:in 133 Dev. Biol. , 109-118. Development , 4131-4143. Development (2006). Theroles ofciliaindevelopmental (2004). From placodetopolarization: newtunes 242 Development Genes Dev. (1997). Tissue polaritypointsfrom cells (1997). Tissue , 149-160. 131 Semin. CellDev. Biol. 133 (2006). Frizzled/RYK mediated Drosophila Development , 4119-4130. Drosophila , 4399-4408. 15 130 , 1182-1187. , 4037-4046. (1998). Dishevelled Drosophila 126 and mammalsthat (Shimada etal., (2003). Basalbody , 4175-4186. 17 , 185-193. Fz Dev. Cell (2002). gene has , Fzand 425 Curr. , 2 , Copp, A.J.,Greene, N.D.andMurdoch, J.N. Fritzsch, B.,Tessarollo, L.,Coppola,E.andReichardt, L.F. Gao, F. B.,Kohwi,M.,Brenman, J.E.,Jan,L.Y. andJan,Y. N. Gao, W. Q. Curtin, J.A.,Quint,E.,Tsipouri, V., Arkell,R.M.,Cattanach, B.,Copp,A.J., Cotanche, D.A.andCorwin,J.T. Casal, J.,Lawrence, P. A.andStruhl,G. Chen, C.M.andStruhl,G. Chandrasekhar, A.,Moens,C.B.,Warren, J.T., Jr, Kimmel,C.B.and Chae, J.,Kim,M.Goo,J.H.,Collier, S.,Gubb,D.,Charlton,J.,Adler, P. N. Classen, A.K.,Anderson,K.I.,Marois, E.andEaton,S. Ciruna, B.,Jenny, A.,Lee,D.,Mlodzik,M.andSchier, A.F. Hamblet, N.S.,Lijam,N.,Ruiz-Lozano, P., Wang, J.,Yang, Y., Luo,Z.,Mei,L., Germino, G. Eley, L.,Turnpenny, L.,Yates, L.M.,Craighead,A.S.,Morgan,D.,Whistler, Eaton, S. Dabdoub, A.,Donohue,M.J.,Brennan, A.,Wolf, V., Montcouquiol,M., Gubb, D.andGarcia-Bellido, A. Hannus, M.,Feiguin, F., Heisenberg,C.P. andEaton, S. Guo, N.,Hawkins,C.andNathans,J. Grebe, M. Goto, T., Davidson,L.,Asashima,M.andKeller, R. Gong, Y., Mo,C.andFraser, S.E. Fischer, E.,Legue,Doyen,A.,Nato,F., Nicolas,J.F., Torres, V., Yaniv, M. Djiane, A.,Yogev, S.andMlodzik,M. Denman-Johnson, K.andForge,A. Davis, E.E.,Brueckner, M.andKatsanis,N. Davies, A.,Formstone,C.,Mason,I.andLewis,J. Greene, N.D.,Gerrelli, D.,Van Straaten,H.W. andCopp,A.J. hair celldevelopmentandregeneration inthechickcochlea. mammalian neurulation. Dev. Cell packing ofDrosophila wingepithelialcellsbytheplanarcellpolaritypathway. disease. guidance. Neurotrophins intheear:theirroles insensoryneuron survivalandfiber between homologousneurons. of dendriticfieldformationinDrosophila: theroles offlamingo andcompetition Biol. tube defectsinthemouse. of Celsr1disruptsplanarpolarityinnerearhaircellsandcausessevere neural Henderson, D.J.,Spurr, N.,Stanier, P., Fisher, E.M.etal. 402. polarity. Dachsous/Fat andStarrynight/Frizzled,actindependentlytoconferplanarcell Frizzled2 proteins ofDrosophila. Development Kuwada, J.Y. a memberoftheprotocadherin family. and Park,W. J. Nature polarity signallingcouplescelldivisionandmorphogenesisduringneurulation. in mice. Chien, K.R.,Sussman,D.J.andWynshaw-Boris, A. Biol. Int. C., Goodship,J.A.andStrachan,T. Opin. CellBiol. 121 dPatj regulate Frizzled-dependentplanarcellpolarityintheDrosophila eye. 28 and orientationinthedevelopingvestibularsystemofmouse. bundles inthemammaliancochlea. (2003). Wntsignalingmediatesreorientation ofouterhaircellstereociliary Sassoon, D.A.,Hseih,J.C.,Rubin,S.,Salinas,P. C.andKelley, M.W. Exp. Morphol. of cuticularpolarityduringdevelopment inDrosophila melanogaster. 59-72. loop-tail (Lp)mouse:amodelofsevere neuraltubedefects. Abnormalities offloorplate,notochord andsomitedifferentiation inthe 26 Curr. Biol. genes regulate polarizedextracellular matrixdepositionduringfrog gastrulation. tube closure. essential forcardiac outflowtractdevelopment,somitesegmentation andneural cell divisionorientationduringzebrafishgastrulation. and Pontoglio,M. 9-19. the vertebratecilium:newfunctionalroles foranancientorganelle. 1 protein. cells inthechickinnereariscorrelated withpolarizeddistributionofc-flamingo- , 821-835. , 719-729. , 621-631. 57 439 , 293-319. (1997). PlanarpolarizationofDrosophila andvertebrateepithelia. Nat. Genet. Proc. Natl.Acad.Sci.USA Development 28 (2004). Upsanddownsoftissueplanarpolarityinplants. 9 (2003). Haircelldevelopmentinhighervertebrates. 15 Dev. Dyn. Prog. BrainRes. , 805-817. , 220-224. , 119-124. , 787-793. Development 124 (2005). LinkingciliatoWnts. 68 (1997). Developmentofbranchiomotorneurons inzebrafish. 9 (1999). TheDrosophila tissuepolaritygenestarrynightencodes , 860-866. , 37-57. , 2633-2644. (2006). Defectiveplanarcellpolarityinpolycystickidney 233 38 133 , 21-23. , 998-1005. Nat. Rev. Genet. , 4561-4572. (1999). Wingless transductionbytheFrizzledand (1999). Wingless 146 Curr. Biol. 129 , 265-278. , 5827-5838. Neuron (1982). Ageneticanalysisofthedetermination Development (2004). Planarcellpolaritysignallingcontrols (1991). Stereociliary bundlesreorient during 101 Development (1999). Establishmentofhairbundlepolarity 13 (2004). Frizzled6controls hairpatterning (2004). Aperspectiveoninversin. (2005). TheapicaldeterminantsaPKCand , 9277-9281. Development 28 (2006). Two separatemolecularsystems, , 1129-1133. 4 , 91-101. , 784-793. Nat. Genet. (2006). Theemergingcomplexityof 126 (2003). Thegeneticbasisof 130 , 5441-5452. (2005). Planarpolarityofhair (2005). Planarcellpolarity 126 Nature Development 134(4) , 2375-2384. 37 (2002). Dishevelled2is , 5421-5429. (2002). Planarcell (2005). Hexagonal , 455-457. (2004). (2006). Planarcell Hear. Res. 430 (2003). Mutation Curr. Top. Dev. Mech. Dev. (2000). Control , 689-693. J. Neurocytol. Dev. Cell (1998). J. Embryol. BioEssays 52 Cell Curr. , 379- 73 Cell 11 , ,

DEVELOPMENT Huangfu, D.andAnderson,K.V. Lewis, J.andDavies,A. Jenny, A.andMlodzik,M. Huangfu, D.andAnderson,K.V. Higashijima, S.,Hotta,Y. andOkamoto,H. Heisenberg, C.P., Tada, M.,Rauch,G.J.,Saude,L.,Concha,M.Geisler, R., Development 134(4) Morgan, D.,Eley, L.,Sayer, J.,Strachan,T., Yates, L.M., Craighead,A.S.and Morgan, D.,Turnpenny, L.,Goodship,J.,Dai,W., Majumder, K.,Matthews, Montcouquiol, M.,Sans,N.,Huss,D.,Kach,J.,Dickman,J.Forge,A., Montcouquiol, M.,Crenshaw, E.B.,3rd andKelley, M.W. Montcouquiol, M.,Rachel,R.A.,Lanford, P. J.,Copeland,N.G.,Jenkins, Mochizuki, T., Saijoh,Y., Tsuchiya, K.,Shirayoshi,Y., Takai, S.,Taya, C., Ma, D.,Yang, C.H.,McNeill,Simon,M.A.andAxelrod, J.D. Lyuksyutova, A.I., Lu,C.C.,Milanesio,N.,King,L.A.,Guo,Wang, Y., Lu, X.,Borchers, A.G.,Jolicoeur, H.,Baker, C.,Rayburn, J.C.andTessier- Keller, R.,Davidson,L.,Edlund,A.,Elul,T., Ezin,M.,Shook,D.and Katanaev, V. L.,Ponzielli,R.,Semeriva,M.andTomlinson, A. Karner, C.,Wharton,K.A.,Jrand Carroll, T. J. Jessen, J.R.,Topczewski, J.,Bingham,S.,Sepich,D.Marlow, F., Klein, T. J.andMlodzik,M. Murdoch, J.N.,Doudney, C., Copp,A.J.andStanier, K.,Paternotte, P. Kelley, M.W. Kennerdell, J.R.andCarthew, R.W. Lawrence, P. A., Casal,J.andStruhl,G. Kimura, H.,Usui,T., Tsubouchi, A.andUemura,T. Lee, R.C.,Clandinin,T. R.,Lee,C.H.,Chen,P. L.,Meinertzhagen,I.A.and Kibar, Z.,Vogan, K.J.,Groulx, N.,Justice,M.J.,Underhill,D.A.andGros, the mouse. under thecontrol oftheislet-1promoter/enhancer. motor neurons inlivetransgeniczebrafishexpressing green fluorescent protein cells acquire theirorientedstructure? selection intheDrosophila visualsystem. G protein-dependent frizzledsignalinginDrosophila. vertebrate organogenesis. mechanism forcellularpolarization. vertebrates. conservation anddivergenceofHedgehogpathwaysfrom Drosophila to Nature mediates convergentextensionmovementsduringzebrafishgastrulation. Stemple, D.L.,Smith,J.C.andWilson,S.W. 2A. polarization requires aB’regulatory subunitofprotein Widerborst, phosphatase involvement inthecell cycle. promoting complexprotein Apc2suggestarole forinversininprimaryciliaand Goodship, J.A. mouse. novel geneinthevertebrateleft-rightaxis pathway, ispartiallydeletedintheinv L., Gardner, A.,Schuster, L.,Harrison,W. G.,Vien, etal. cell polarityinmammals. Asymmetric localizationofVangl2 andFz3indicate novelmechanismsforplanar Rachel, R.A.,Copeland,N.G.,Jenkins,Bogani,D.etal. 386. Noncanonical Wntsignalingandneuralpolarity. polarity genesinmammals. A. andKelley, M.W. 395 inv, agenethatcontrols left/rightasymmetryandkidneydevelopment. Yonekawa, H.,Yamada, K.,Nihei,H.,Nakatsuji,N. etal. Fidelity inplanarcellpolaritysignalling. 1988. guidance ofcommissuralaxonsbyWnt-frizzledsignaling. Nathans, J.,Tessier-Lavigne, M.andZou,Y. vertebrates. Lavigne, M. intercalation. Skoglund, P. 4 new roles forStrabismusingastrulationandneuronal movements. Chandrasekhar, A.andSolnica-Krezel, L. points intherightdirection. Flamingo indendriticmorphogenesis. molecular interactionoftheDrosophila 7-passtransmembranecadherin pathway. interference todemonstratethatfrizzledand2actinthewingless development, includingnotchanditsligands. polarity intheabdominalepidermisofDrosophila. 255. Zipursky, S.L. altered inthemouseneuraltubemutantLoop-tail. is P. , 610-615. (2001). Ltap,amammalianhomologofDrosophila Strabismus/Van Gogh, , 177-181. Development 405 Nat. Genet. Cell , 76-81. Proc. Natl.Acad.Sci.USA Development Nature (2003). Celladhesionmoleculesduringinnerearandhaircell (2004). PTK7/CCK-4isanovelregulator ofplanarcellpolarityin Philos. Trans. R.Soc.Lond.BBiol.Sci. (2000). Mechanismsofconvergenceandextensionbycell 95 (2003). Theprotocadherin Flamingoisrequired foraxontarget , 1017-1026. (2002). Expression analysesandinteractionwiththeanaphase 129 430 20 , 3493-3503. (2003). IdentificationofVangl2 andScrb1asplanar , 149-156. (2002). Planarcellpolarityintheinnerear:howdohair , 93-98. J. Neurosci. 133 (2006). Planarcellpolaritysignaling:acommon Semin. CellDev. Biol. (2005). Planarcellpolarization:anemergingmodel Nature Annu. Rev. CellDev. Biol. Hum. Mol.Genet. , 3-14. (2005). CiliaandHedgehogresponsiveness in (2006). Signalingfrom SmotoCi/Gli: 423 Mt. SinaiJ.Med. (1998). UseofdsRNA-mediatedgenetic 26 J. Neurobiol. 102 J. CellSci. (2004). Cellinteractionsandplanar , 173-177. Nature , 5265-5275. Nat. Neurosci. , 11325-11330. (2000). Visualization ofcranial (2000). Visualization (2002). Zebrafishtrilobiteidentifies Curr. Top. Dev. Biol. 421 (2006). Planarcellpolarityand (2003). Anterior-posterior 11 17 Annu. Rev. Neurosci. 119 (2000). Silberblick/Wnt11 Development , 3345-3350. 53 , 194-203. , 543-547. 355 J. Neurosci. (2006). Potentialdual , 1118-1129. , 190-201. Cell 73 21 Nat. Genet. , 897-922. 6 , 738-750. , 155-176. , 557-563. 120 Science (2006a). (1998). Inversin,a (1998). Cloningof , 111-122. 131 20 (2005). Trimeric 302 57 , 206-218. , 4651-4664. Nat. CellBiol. (2003). 28 (2006b). , 321-356. 29 , 1984- , 251- Nature , 363- Murdoch, J.N.,Henderson,D.J.,Doudney, K.,Gaston-Massuet,C.,Phillips, Nurnberger, J.,Kribben,A.,Opazo Saez,A.,Heusch,G.,Philipp,T. and Pan, C.L.,Howell,J.E.,Clark,S.G.,Hilliard, M.,Cordes, S.,Bargmann,C.I. Simons, M.,Gloy, J.,Ganner, A.,Bullerkotte,Bashkurov, M.,Kronig, C., Shimada, Y., Yonemura, S.,Ohkura,H., Strutt,D.andUemura,T. Otto, E.A.,Schermer, B.,Obara,T., O’Toole, J.F., Hiller, K.S.,Mueller, A.M., Okada, Y., Nonaka,S.,Tanaka, Y., Saijoh,Y., Hamada,H.andHirokawa, N. Park, T. J.,Haigo,S.L.andWallingford, J.B. Park, F. D.,Tenlen, J.R.andPriess, Price, D.J.,Kennedy, H.,Dehay, C.,Zhou,L.,Mercier, M.,Jossin, Y., Goffinet, Thorpe, C.J.,Schlesinger, A.,Carter, J.C.andBowerman,B. Taylor, J.,Abramova,N.,Charlton,J.andAdler, P. N. Strutt, H.andD. Strutt, D.I.,Weber, U.andMlodzik,M. Strutt, D.I. Singla, V. andReiter, J.F. Rocheleau, C.E.,Downs,W. D.,Lin,R.,Wittmann,C.,Bei,Y., Cha,Y. H.,Ali, Strutt, D.I. Slusarski, D.C.,Corces, V. G.and Moon,R.T. Tissir, F., Bar, I.,Jossin, Y., DeBacker, O.andGoffinet, A.M. Romand, R.,Dolle,P. andHashino,E. Shimada, Y., Usui,T., Yanagawa, S.,Takeichi, M.andUemura,T. Senti, K.A.,Usui,T., Boucke,K.,Greber, U.,Uemura,T. andDickson,B.J. Rosso, S.B.,Sussman,D.,Wynshaw-Boris,A.andSalinas,P. C. Ross, A.J.,May-Simera,H.,Eichers,E.R.,Kai,M.,Hill,Jagger, D.J., Shima, Y., Kengaku,M.,Hirano,T., Takeichi, M.andUemura,T. mouse. Disruption ofscribble(Scrb1)causessevere neuraltubedefectsinthecircletail C.,Arkell,R.,Stanier,H. M.,Paternotte, P. andCopp,A.J. 2593-2601. wing epithelium. Polarized transportofFrizzledalongtheplanarmicrotubule arraysinDrosophila Am. Soc.Nephrol. Phillips, C.L. of Lpp1,anovelgeneinvolvedinfloorplatespecification. (2001). Severe neuraltubedefectsintheloop-tailmouseresult from mutation Genet. disease tothefunctionofprimaryciliaandleft-rightaxisdetermination. asymmetrically priortocelldivision. functions inMOM-2/Wnt-independentcellpolarityandislocalized 10 directed cellandgrowth conemigrationsinCaenorhabditiselegans. and Garriga,G. Drosophila. planar polaritypathway. switch betweenWntsignalingpathways. the geneproduct mutatedin nephronophthisis typeII,functionsasamolecular Schermer, B.,Benzing,T., Cabello,O.A.,Jenny, A.etal. INVS encodinginversincausenephronophthisis type Ruf, R.G.,Hoefele,J.,Beekmann,F., Landau,D.etal. 4 (1999). Abnormalnodalflowprecedes situsinversusinivandinvmice. cell polarityandHedgehogsignaling. orfuzzyfunctionareembryos lackinginturned associatedwithfailure ofplanar connections. A. M.,Tissir, F., Blakey, D.andMolnar, Z. Drosophila tissuepolaritygene. polarity andFrizzledsignalling. cell polarityintheDrosophila wing. signaling atasensoryorganelle. mesoderm. signaling polarizesanearlyC.elegansblastomere todistinguishendoderm from gene specifyendoderminearlyC.elegansembryos. M., Priess,J.R.andMello,C. Nature Frizzled homologuetriggersG-protein-linked phosphatidylinositolsignalling. 451-457. Protocadherin Celsr3iscrucialinaxonaltractdevelopment. development. and Dishevelledinplanarcellpolarization. Asymmetric colocalizationofFlamingo,aseven-passtransmembranecadherin, transmembrane cadherin. Regulation ofdendriticmaintenanceandgrowth byamammalian7-pass Drosophila visualsystem. (2003). Flamingoregulates R8axon-axonandaxon-targetinteractionsinthe Nat. Neurosci. signaling through Dishevelled,RacandJNKregulates dendritic development. vertebrates. of Bardet-Biedl syndrome ciliaryproteins perturbsplanarcellpolarityin Leitch, C.C.,Chapple,J.P., Munro, P. M.,Fisher, S.etal. , 459-468. , 367-377. 34 390 Hum. Mol.Genet. , 413-420. (2002). Theasymmetricsubcellularlocalisationofcomponentsthe (2001). Asymmetriclocalizationoffrizzledandtheestablishment , 410-413. Cell BioEssays Nat. Genet. Eur. J.Neurosci. (2004). TheInvsgeneencodesamicrotubule-associated protein. J. Neurobiol. 8 , 34-42. 90 (2006). MultipleWntsandfrizzledreceptors regulate anteriorly Dev. Cell , 695-705. 15 , 1700-1710. 27 (2005). Long-rangecoordination ofplanarpolarityin , 1218-1227. 37 Semin. CellDev. Biol. (2006). Theprimaryciliumasthecell’s antenna: Curr. Biol. Dev. Cell 10 12 , 1135-1140. 66 , 209-222. , 87-98. 23 , 687-704. Nature Genetics , 910-920. Science (1997). WntsignalingandanAPC-related 7 13 Mol. Cell Curr. Biol. , 205-216. Nat. Genet. (2006). Retinoidsignalingininnerear , 828-832. 387 (2004). C.elegansMOM-5/frizzled 313 (1997). Therole ofRhoAin tissue 150 Nat. Genet. Curr. Biol. , 292-295. (2006). Thedevelopmentofcortical , 629-633. , 199-210. 7 (2006). Ciliogenesisdefectsin 13 14 (1997). InteractionofWntanda , 367-375. , 225-231. , 2252-2258. 38 , 303-311. 2 Cell 11 , linkingrenal cystic 37 (1998). Van Gogh:anew , 859-863. , 537-543. 90 Hum. Mol.Genet. (2003). Mutationsin , 707-716. REVIEW Nat. Neurosci. (2005). Disruption (2005). Inversin, (2005). (2003). (1997). Wnt (2005). Wnt (2004). (2001). (2006). Dev. Cell Mol. Cell Nat. 8 657 , 10 J. ,

DEVELOPMENT Veeman, M.T., Slusarski,D.C.,Kaykas,A.,Louie,S.H.andMoon,R.T. Usui, T., Shima,Y., Shimada,Y., Hirano,S.,Burgess,R.W., Schwarz,T. L., Tree, D.R.,Ma,andAxelrod, J.D. 658 Wang, J.,Mark,S., Zhang,X.,Qian,D.,Yoo, S.J.,Radde-Gallwitz,K.,Zhang, Venema, D.R.,Zeev-Ben-Mordehai, T. andAuld,V. J. Uemura, T. andShimada,Y. Wang, J.,Hamblet, N.S.,Mark,Dickinson,M.E.,Brinkman,B.C.,Segil, Wallingford, J.B.,Fraser, S.E.andHarland,R.M. Wallingford, J.B.,Rowning,B.A.,Vogeli, K.M.,Rothbacher, U.,Fraser, S.E. Wallingford, J.B.andHabas,R. Wada, H.,Tanaka, H.,Nakayama,S.,Iwasaki,M.andOkamoto,H. Wada, H.,Iwasaki,M.,Sato,T., Masai,I.,Nishiwaki,Y., Tanaka, H.,Sato,A., C.R.andAdler,Vinson, P. N. regulates gastrulationmovements. (2003). Zebrafishprickle,amodulatorofnoncanonicalWnt/Fzsignaling, 585-595. cadherin, regulates planarcellpolarityunderthecontrol ofFrizzled. Takeichi, M.andUemura,T. axes inDrosophila andvertebrates. regulation ofplanarcellpolarity. pathway. polarized extensionandplanarcellpolarityinthecochleabyvertebratePCP Y., Lin,X.,Collazo,A.,Wynshaw-Boris,A.etal. hairs inDrosophila. polarization ofGliotactinandCoracleisrequired forparallelalignmentofwing development. extension: themolecularcontrol ofpolarizedcellmovementduringembryonic gastrulation. and Harland,R.M. Development Dishevelled: anenigmaticproteincellfateandpolarity. governing 4749-4759. facial motorneurons inthedevelopingzebrafishhindbrain. Frizzled3a andCelsr2functionintheneuroepithelium toregulate migrationof embryos. Scribble1 inneuralmigrationandconvergentextensionmovementszebrafish Nojima, Y. andOkamoto,H. 329 transmission ofpolarityinformationbythefrizzledgeneDrosophila. , 549-551. REVIEW Nat. Genet. Development Nature 132 Dev. Cell , 4421-4436. Dev. Biol. 405 (2000). Dishevelledcontrols cellpolarityduringXenopus 37 2 132 , 81-85. , 980-985. , 695-706. , 2273-2285. (2003). Breaking cellularsymmetryalongplanar (1987). Directional non-cellautonomyandthe 275 (1999). Flamingo,aseven-passtransmembrane (2005). Dualroles ofzygoticandmaternal (2006). Thedevelopmentalbiologyof Semin. CellDev. Biol. , 301-314. Curr. Biol. J. Biochem. (2002). Athree-tiered mechanismfor 13 134 , 680-685. , 625-630. (2002). Convergent (2005). Regulationof 13 (2004). Transient apical , 217-224. Development Cell (2006). Nature 98 133 , , Wright, T. J.andMansour, S.L. Yang, C.H.,Axelrod, J.D.andSimon,M.A. Xu, Q.,Wang, Y., Dabdoub,A.,Smallwood,P. M.,Williams,J.,Woods, C., Yen, H.J.,Tayeh, M.K.,Mullins,R.F., Stone,E.M.,Sheffield, V. C.and Wang, Y., Thekdi,N.,Smallwood,P. M.,Macke,J.P. andNathans,J. Wong, L.andAdler, P. N. Wolff, T. andRubin,G.M. Wang, Y., Badea,T. andNathans,J. Wilson, E.B. Watanabe, D.,Saijoh,Y., Nonaka,S.,Sasaki,G.,Ikawa,Y., Yokoyama, T. and Wang, Y., Guo,N.andNathans,J. Wang, Y., Zhang,J.,Mori,S.andNathans,J. convergent extensionduringneurulation. Dishevelled genesmediateaconservedmammalianPCPpathwaytoregulate N., Fraser, S.E.,Chen,P., Wallingford, J.B.andWynshaw-Boris,A. eye. fat-like cadherinsduringplanarpolaritysignalingintheDrosophila compound innervation. 209-221. high-affinity ligand-receptor pair. development intheretina andinnerear:control byNorrin andFrizzled-4,a Kelley, M.W., Jiang,L.,Tasman, W., Zhang,K.etal. Genet. retrograde intracellulartrafficking andKupffer’s vesicleciliafunction. Slusarski, D.C. Neurosci. neural tubeclosure andintheplanarpolarityofinner-ear sensoryhaircells. CNS. Frizzled-3 isrequired forthedevelopmentofmajorfibertractsinrostral the subcellularlocationforprehair initiationinpupalwingcells. polarity andcellfatedecisionsinDrosophila. MacMillan. organization inmammalianhairpatterning. monocilia andother9+0cilia. Hamada, H. 19800-19805. cell labeling. magnetic resonance imaging,neurofilament staining,andgeneticallydirected guidance defectsinFrizzled3knock-outmice:acomparisonofdiffusion tensor Cell J. Neurosci. 15 108 26 , 667-677. (1925). Curr. Top. Dev. Biol. , 2147-2156. , 675-688. J. Neurosci. (2003). Theleft-rightdeterminantInversinisacomponentofnode (2006). Bardet-Biedl syndrome genesare importantin 22 The CellinDevelopmentandHeredity , 8563-8573. 26 (1998). Strabismus,anovelgenethatregulates tissue (1993). Tissue polaritygenesofDrosophila regulate(1993). Tissue , 355-364. Development (2003). FGFsignalingineardevelopmentand 57 Cell (2006b). Therole ofFrizzled3andFrizzled6in , 225-259. (2006c). Order from disorder: self 116 , 883-895. Development Proc. Natl.Acad.Sci.USA 130 Development 20) RegulationofFrizzledby (2002). (2006a). Axonalgrowth and , 1725-1734. Development 134(4) 133 (2004). Vascular . NewYork: 125 , 1767-1778. , 1149-1159. J. CellBiol. Hum. Mol. 103 (2002). (2006). , 123 J. ,

DEVELOPMENT