DEVELOPMENT OF THE HEAD AND NECK
PlacodesPlacodes andand thethe developmentdevelopment ofof organsorgans ofof specialspecial sensesense
LL.. MMoossss--SaSalelentijnntijn Innovations in the early evolution of vertebrates
! DDeevveellooppmmeenntt ooff oorrggaannss ooff ssppeecciiaall sseennssee ((ppllaaccooddeess)) ! DDeevveellooppmmeenntt ooff aa llaarrggee nneeuurraall cciirrccuuiittrryy ((tthhee bbrraaiinn)) ttoo iinntteeggrraattee iinnppuutt aanndd rreessppoonnsseess ! DDeevveellooppmmeenntt ooff aann eeffffeeccttiivvee ffeeeeddiinngg aappppaarraattuuss (jaws)(jaws) ! DDeevveellooppmmeenntt ooff aann iimmpprroovveedd rreessppiirraattoorryy aappppaarraattuuss ((ggiillllss))
PLACODES
Localized thickened areas of specialized ectoderm, lateral to the neural crest, at the border between neural plate and the future epidermis Brugmann SA, Moody SA (2005) Brugmann SA, Moody SA (2005) NEURAL PLATE
NEURAL GROOVE Example: otic placode. Different kinds of placodes ! CCoonnttrriibbuuttiinngg ttoo oorrggaannss ooff ssppeecciiaall sseennssee:: "OlfactoryOlfactory "LensLens (only(only placodeplacode thatthat doesdoes notnot havehave neuralneural fate)fate) "OticOtic ! ContributingContributing toto distaldistal gangliaganglia ofof branchiomericbranchiomeric nneerrvveess:: "TrigeminalTrigeminal (Ophthalmic,V1)(Ophthalmic,V1) "EpibranchialEpibranchial (4)(4) ! Hypobranchial (2) (contribute to hypobranchial ganglia - frog only; not in chick, mouse, zebrafish) Distribution of placodes at 3 developmental stages
A. Initial induction of placodes in pre-placodal ectoderm field B. Olfactory placodal cells are incorporated in outer folds of anterior neural ridge Fate maps of cephalic placodes in zebrafish, chick and salamander
Schlosser G (2006) Transcription factor expression domains
Schlosser G (2006) Development of placodes: similarities
! UndeUnderr influeinfluencncee ofof surroundingsurrounding tissuetissuess –– nnoo evidenceevidence forfor rolerole ofof neuralneural crestcrest inin thisthis pprroocceessss ! AAllll eexxpprreessss oonnee oorr mmoorree mmeemmbbeerrss ooff PaxPax ffaammilyily aass ttrarannscscrriptioniption ffaaccttorsors eeaarrlyly iinn ddeevveellooppmmeenntt Development of placodes - differences ! EEppiibbrraanncchhiiaall ppllaaccooddeess:: pphhaarryynnggeeaall eennddooddeerrmm ((BBMMPP--77 signal),signal), Pax2Pax2 andand Sox3Sox3 ! OOpphhtthhaallmmiicc ppllaaccooddee ofof V:V: nneeuurreeccttooddeerrmm ooff mmeesseenncceepphhaalloonn ((difdifffusibleusible signasignall ??)),, PPaax3x3 ! OOttiicc ppllaaccooddee:: iinniittiiaallllyy aaxxiiaall aanndd nnoonn--aaxxiiaall mmeessooddeerrmm,, PPaaxx 88;; llaatteerr hhiinnddbbrraaiinn ((FFGGFF--33,,--88,,--1010 signasignals)ls),, PPaax2,x2, SSox3,ox3, NotcNotchh ! LensLens ppllaaccooddee:: ffoorreebbrraaiinn && aanntteerriioorr mmeessooddeerrmm ((BBMMPP--4,4, laterlater BMPBMP--77 signals),signals), Pax6,Pax6, laterlater Pax2Pax2 ! OOllffaaccttoorryy ppllaaccooddee:: aantenterriorior memesodesoderrmm ((aandnd ffoorreebbrraaiinn?? –– nnoo ssiiggnnaall iiddeennttiiffiieedd aass yyeett)),, PPaaxx66 Location of placodes
! NNeeaarr ffoorreebbrraaiinn ::
"OlfactoryOlfactory placodeplacode
"LensLens placodeplacode Location of placodes
! DDoorrssoollaatteerraall :: OticOtic placodeplacode:: relatedrelated toto (=(= evolvedevolved fromfrom oror havinghaving commoncommon originorigin with)with) laterallateral lineline systemsystem
Location of placodes
! InteIntermermediatediate betweenbetween oticotic placplacodeode andand epibranchialepibranchial ppllaaccooddeess :: OphthalmicOphthalmic componentcomponent ofof trigeminaltrigeminal placodeplacode Streit A (2004) Schlosser G (2006) Location of placodes
! EpibranchialEpibranchial sseerriieess –– dorsaldorsal endsends ofof 11st –– 44th pharyngealpharyngeal groovesgrooves ! HypobranchialHypobranchial sseerriieess inin frogsfrogs –– ventralventral endsends ofof 22nd –– 33rd pharpharyngeyngealal grgrooveoovess ?? 1. Olfactory 2. Otic 3. Trigeminal (V) 4. Facial (VII) 5. Glossopharyngeal (IX) 6. Vagal (X)
Branchiomeric nerves: origins and axon projection patterns Development of organs of special sense Olfactory epithelium: development of the nose Olfactory epithelium: development of the nose
Transient pioneer neurons set up scaffold
Olfactory epithelium 6868--8484 daysdays
4646--5454 daysdays Dulac C (2006) Olfactory placode gives rise to:
!! SensorySensory receptorreceptor cellscells ofof olfactoryolfactory epitheliumepithelium ofof thethe nosenose (odorant(odorant sensing)sensing) !! SensorySensory receptorreceptor cellscells ofof vomeronasalvomeronasal epitheliumepithelium (pheromone(pheromone sensing)sensing) !! BasalBasal cellscells andand supportsupport cellscells (olfactory(olfactory eennsshheeaatthhiinngg cceellllss -- gglliiaa)) Development of the eye : 1. evagination of forebrain (optic vesicle) 2. invagination of lens placode Optic vesicle forms optic cup under influence of lens primordium. Between developing lens vesicle and optic cup : primary vitreous body. HyaloidHyaloid AA..:: terminalterminal branchbranch ofof ophthalmicophthalmic A.A. (future(future centralcentral arteryartery ofof retina)retina)
In lens vesicle posterior cells elongate to form primary lens fibers. In third month anterior epithelium elongates to form secondary lens fibers (most of mature lens) Optic cup: Inner layer neural retina Outer layer pigment retina Optic stalk: Axons from neural retina grow through the choroidal fissure to brain optic nerve NC derived mesenchyme around the optic cup: Thin inner choroid Outer fibrous sclera NC derived mesenchyme anterior to lens: Anterior layer contributes to cornea Posterior layer pupillary membrane Between anterior and posterior layers: anterior chamber of eye Behind posterior layer: posterior chamber. Development of inner ear Otic placode invagination: otic pit Otic pit to otic vesicle
Some placodal cells migrate out of vesicular wall: statoacoustic ganglion of CN VIII Differential growth of otic vesicle
Saccule: ventral, will give rise to mature saccule and cochlea. Utricle: dorsal, will give rise to mature utricle, semicircular canals and endolymphatic duct.
Otic capsule: future petrous part of temporal bone