in the nervous system

Arthur D. Lander

Massachusetts Institute of Technology, Cambridge, USA

Proteoglycans are ubiquitous ceil-surface and secreted that are involved in diverse cellular behaviors. The identities of several nervous system proteoglycans, including many of the major species in the mammalian brain, have recently come to light. In addition, recent studies have given new insights into the roles of proteoglycans in nervous system development and function.

Current Opinion in Neurobiology 1993, 3:71fS-723

Introduction polysaccharides, typically 20-200 sugars in length, which are usually attached via a characteristic linkage region Proteoglycans (PGs) are found on the surfaces of all ad- to serine residues. GAGS are built by the sequential herent cells, within intracellular vesicles, and in virtually addition of identical disaccharide units onto this link- all extracellular matrices (ECMS). They are evolutionar- age region. Only three types of disaccharide may be ily ancient molecules, and play functional roles in the used, giving rise to three families of GAGS: the hep- biology of growth factors, extracellular proteolysis, cell arin/heparan family [ D-glucuronic acid p(1+4) D-N- adhesion, lipoprotein metabolism, and virus entry into acetyl glucosamine a( l-4)] *; the chondroitin/dermatan cells, as well as structural roles in maintaining the physical family [D~glucuronic acid [3(1+3) D-N-ace@ galac- and mechanical properties of ECMs [ 1,2*,3,4], tosamine p( l-+4)] n; and the keratan family [ D-galactose p(1+4) D-N-acetyl glucosamine 0(1+3)],. The sugars of Although many basic characteristics of PGs - their num- most GAGS are further chemically modified, typically in a ber, their structures, the exact nature of the functions sporadic fashion throughout the chain, by Osulfation, N they perform - are still slowly emerging, great progress deacetylation followed by N-sulfation, and/or epimeriza- has been made in recent years. With this recent burst tion (isomerization) of glucuronic acid to iduronic acid. of activity has come increasing recognition of the signifi- Subsequently, GAGS are referred to as heparin, heparan cance of PGs by neurobiologists, and increasing interest sulfate (HS), (CS), dermatan sulfate in the postulated roles PGs play in the nervous system. (DS) or (KS). The heparin/HS distinction Some investigators have isolated monoclonal antibodies and the CS/DS distinction only reflect differences in level against nervous system molecules that have turned out of modification (i.e. heparin is more highly modified than to be PGs. Other investigators have become intrigued most HS species; DS contains much more iduronate than by the fact that many of the molecules that are thought CS). As each disaccharide in a GAG chain may be mod- to inlluence neuronal and glial cell behavior in vivo, es- ified to a different degree, the large scale structures of pecially during development, bind PGs. In the last few GAGS can be exceedingly complex (e.g. in HS, which can years, direct assaults on determining the structures of be modified in up to five ways, a hexasaccharide can the- central nervous system (CNS) PGs have been under- oretically have over 30,000 possible chemical structures). taken by several groups. The purpose of this article is to review some of these recent results, and place them Products of several families, including secreted and into the wider context of what PGs are, and how they are membrane-inserted polypeptides, act as the core thought to function. of major PGs (Table 1). Some bear as few as one GAG chain, whereas others have over a hundred. Although the signals that specify whether a serine residue will bear a GAG are partially understood [2*], it is not known what controls the type of GAG synthesized: examples exist of What are PCs? cores that always bear one type of GAG, cores that bear different GAGS at different sites, and cores that bear dif- A is called a PG if it contains a covalently ferent GAGS depending on the cell type in which they are attached glycosaminoglycan (GAG). GAGS are linear expressed.

Abbreviations CNS-central nervous system; CS-chondroitin sulfate; DS-dermatan sulfate; ECM---extracellular matrix; FCF-fibroblast growth factor; GAG--glycosaminoglycan; HS--; KS-keratan sulfate; NCAM-neural molecule; N&AM-neuron-gliai cell adhesion molecule; PC-.

716 @ Current Biology Ltd ISSN 0959-4388 Proteoglycans in the nervous system Lander 717

brain HSPG Ml2 identified by us [G], are the rat form rable 1. Cloned PC core prote1ns.a of (IS]; ED Litwack, CS Stipp, A Kumbasdr, AD - Lander, unpublished data). Irz situ hybridization studies M-surlace PCs in the adult brain and spinal cord indicate that glypi- Syndecan family can mKNA is expressed primarily, if not exclusively, by Syndecan (Syndecan-I) projection neurons in many, but not all parts of the Fibroglycan (Syndecan-2) CNS (ED Litwack, CS Stipp, A Kumbasar, AD Iander, un- N-SyndecaniSyndecan-3 published data) (see Table 2). In the embryo, glypican is Ryudican/Amphlglycan/Syndecan-4 also strongly expressed in ventricular zones (regions un- Clypican family dergoing neural precursor proliferation) throughout the Clypican neuraxis (Fig. 1). Cerebroglycan

NC-2

‘Part-time PGs’b

Cerebroglycan KM PCs Cerebroglycan, previously called PG Ml3 [6], is an HSPG family with a -58 kDa core protein, and was first detected in Aggrecan the embryonic and newborn - but not adult - rat brain. Like glypican, it is glycosylphosphatidylinositol- Neurocan anchored. In fact, glypican and cerebroglycan define a Small, interstitial PC family family of lipid-anchored HSPG cores, based on amino acid sequence similarity (CS Stipp, ED Litwack, AD Ian- der, unpublished data) (see Table 2). In situ hybridiza- Fibromodultn tion studies indicate that cerebroglycan is transiently ex- pressed by postmitotic neurons throughout the CNS (Fig. 1). Evidently, cerebroglycan mRNA appears in neurons Type IX Collagen shortly after terminal mitosis and disappears after neu- ronal migration and axon growth have been completed. ntravesicular PCs Interestingly, cerebroglycan is not expressed outside the Serglycin nervous system. sv2 -

‘Only shown are the obligate PC core proteins, i.e. those that

wanably bear GAG chains A small number of other cell-surface N-syndecan xoteins bear GAG chains in some cells, but not others. bThese N-syndecan (or syndecdn-3) is one of four members of part-time’ PCs Include CD44 and the type 111transforming growth the syndecan family of transmembrane core proteins actor cTGF)-p receptor (reviewed in 11,2*,531). (Table 1). These polypeptides have short (-34 amino acids) cytoplasmic domains that are highly conserved among all family members, and overall sizes varying from 20 kDa (syndecans-2 and -4) to 2 42 kDa (syndecan- 3). Their extracellular domains are poorly conserved among the different family members, or even for the Cell surface PCs of the CNS same syndecan in different mammalian species. N-syn decan was cloned by Carey et al. [9**], who identified Early progress toward identifying cell surface PGs of the it in rat Schwann cell membranes (see Table 2). High brain was made by Margolis’ group, who detected a sin- levels of Nsyndecan mRNA are also found in neonatal gle major HSPG in adult brain membranes [5]. Later, rat brain, as well as in many sites outside the nervous Herndon and I 161 found evidence for CSPGs and other, system. Expression of this molecule in rat brain peaks less abundant, HSPGs in adult brain membranes, as well at birth, declining to undetectable levels thereafter. Early as additional major HSPGs that are present only during immunohistochemical studies suggest that this PG is as- development. In the past year, the core proteins of sev- sociated with fiber tracts, but it is not yet known whether eral of these have been identified. its source is neuronal or glidl.

Glypican Syndecan-2 Glypican was first identified as a surface HSPG core pro- Syndecan-2, also known as fibroglycan, another member tein of human fibroblasts [7], The mature polypeptide of the syndecan family, has not yet been isolated from is 53 kDa and is anchored in the plasma membrane the brain, but its mRNA has been found there (see Table by covalently attached glycosylphosphatidylinositol. Both 2). Based on electrophoretic behavior, syndecan-2 may the adult brain HSPG identified by Klinger et al. [ 51, and correspond to brain PG Ml4 [6]. 718 Neuronal and glial cell biology

Table 2. PCs of the mammalian CNS.a

Name Family GAG CNS Expression

Syndecan-3 Syndecan HS Transiently expressed in perinatal brain; widespread [9-*1

Glypicanb Glypican HS Neuroepithelium; certain adult projection neurons [81c

Cerebroglycanb Clypican HS Transiently expressed by newly post-mitotic neuronsd

NC-2 NC-2 cs O-2A progenitors [IO1

Syndecan-2 Syndecan HS Unknown [2*1

Neurocan (1 Dl) Aggrecan CS White matter of developing cerebellum; molecular layer of adult cerebellum. Mostly intracellular in adult [12**,181 Versican Aggrecan cs White matter 113.1

Aggrecan Aggrecan cs Embryonic chick brain 114.1

Cat-301 Aggrecan? cs Subsets of neurons, cerebellum and spinal cord [15*,201

PC-T1 ? cs Widespread [16**,17~1

3Hl ? CSIKS Similar to neurocan [I81

3F8 ? cs Concentrated in molecular layer of developing and adult cerebellum I181 684 ? cs Cerebellar and brainstem projection neurons I19.1

Unnamed ? HS Transient, in CNS fiber tracts [26**1

SV2 antigen sv2 KS Synaptic vesicles [27**1

aPCs are referred to by the names of their core proteins, and are grouped according to whether they are cell surface, extracellular matrix/soluble, or intravesicular molecules (see text). In many cases, information on CNS distribution has been based on the examination of only a few brain regions, and is therefore incomplete. bData on distribution of glypican and cerebroglycan are based on rn situ hybridization; most other data were obtained using antibodies. cED Litwack, CS Stipp, A Kumbasar, AD Lander, unpublished data. dCS Stipp, ED Litwack, AD Lander, unpublished data.

NC2 Most of the PGs in these categories contain CS as their NG2 is a transmembrane CSPG with a 300 kDa core pro- major GAG. Neurocan, a recently cloned CSPG, has a 136 tein [ 101. In the brain it is associated with a population kDa core protein, and contains N 3 CS chains [ 12**]. of glial precursor cells, the O-2A progenitors (see Table Its protein sequence places it in a family with aggre- 21, that give rise to oligodendrocytes and a type of as can - the major ECM PG of cartilage - and versican, trocyte. The very large core protein of NG2 suggests that an ECM PG first found associated with libroblasts. Like it may serve functions other than just bearing CS chains. these other PGs, neurocan binds the ECM polysaccha- One such function appears to be the binding of type VI ride hyaluronic acid via a protein domain that is highly collagen [ 11 I. conserved in all three family members. Recent evidence suggests that versican and aggrecan are themselves ex- pressed in the human and chicken brain, respectively [ 130,14*], The Cat-301 antigen is yet another large brain ECM and ‘soluble’ PCs of the CNS CSPG that binds hyaluronic acid, and immunological ev- idence suggests that it is related to aggrecan [15*]. One Many PGs can be extracted from the brain using phys- additional hyaluronic acid-binding CSPG, the Tl antigen, iological buffers without detergent; others require high has been identified in brain, but at least the hyaluronic salt or denaturing conditions. Although it has been ar- acid-binding region of this molecule is apparently unre- gued that some of these molecules may reside in the lated to those of the aggrecan family [ 16-e,17*]. Still other cytoplasm of cells, most are probably loosely associated brain CSPGs have been identified with monoclonal anti- with the ECM. bodies, and remain to be fully characterized [ 14~,18,19=]. Proteoglycans in the nervous svstem Lander 719

Fig. 1. Expression of glypican and cerebroglycan in the rat embryo Adjacent sections of embryonic day 14 rats were hybridized with radiolabeled RNA probes specific for (a) glypican and (b) cerebroglycan mRNA. The images are reverse contrast prints of the resulting autoradiograms. Glypican expression is found throughout the embryo, but is particularly strong in the ventricular zones of the developing CNS. In contrast, cerebroglycan mRNA, which is found only in neural tissue, is not detected in ventricular zones but is found in the layers of immature neurons that form around those zones. In the adult brain, glypican IS expressed by subpopulations of neurons, whereas cerebroglycan is absent. fb-forebrain; rnb-midbrain; hb-hindbrain; tg-trigeminal ganglion.

The distributions of these CSPGs vary from remarkably protein size (250 kDa) and basal laminar distribution of uniform throughout the brain (PG Tl) to remarkably this PG are reminiscent of perlecan, a major basement cell type- and developmental stage-specific. For example, membrane PG, but perlecan itself is not found in CNS Cat-301 appears around certain subsets of neurons only axon tracts. after activity-dependent critical periods in their develop- ment [ 201. Another is transiently expressed during axon outgrowth by several types of neurons involved in the cerebellar mossy fiber system [19-l, Synaptic vesicle PCs As information on the distribution of these CSPG and It has long been known that a PG is a major component CS/KSPG core proteins accumulates, so has information of synaptic vesicles isolated from the electric organs of on the distribution of different types of CS and KS chains. lishes. This PG was recently shown to be a transmem Several investigators have observed remarkable cell-type brane KSPG, and appears to be involved in acetylcholine specificity in the binding of anti-CS and anti-KS mono- transport into vesicles [27-l Immunochcmical data sug- clonal antibodies to brain sections (e.g. [ 21,221). During gest that this molecule is present in many other types of cerebral cortex development, CS is found in the early synaptic vesicles, and might therefore play an important proliferative neuroepithelium, then later in the marginal general role in transmitter uptake. zone and subplate regions [23]. With the exception of the subplate, many of the locations of CS expression during development correlate with sites where axons do not grow. For example, CS, as well as KS, are strongly expressed in the roof plate of the spinal cord [24,25]. Roles of PCs in the nervous system

Recently, a report of an HSPG in brain ECM appeared Insights into the functions of PGs in the nerous system [26-l. ?his molecule is found in basal laminae outside of have come t3y many routes, direct and indirect, and man) and surrounding the chicken brain, but is also expressed of the conclusions are still somewhat pr&minan: I I&h transiently in many developing CNS axon tracts. The core lights of what has heen learned are summarized below. 720 Neuronal and glial cell biology

The functions of a family of growth factors are glial cell adhesion molecule (NgCAM)-binding [489]. A dependent on PCs HSPG released by Schwannoma cells specifically blocks the neurite outgrowth-promoting activity of laminin [49]. All members of the fibroblast growth factor (FGF) fam In some of these cases, the GAG chains of the PGs are re- ily bind GAGS of the heparin/HS class, and apparently quired for these actions [ 24,25,49] ; in others they are not must do so to be biologically active [28,29]. Recent stud- [47,48*]. It is not yet known whether these phenomena ies support a model in which cell-surface HSPGs bind are direct actions of PGs on neurons, or reflect effects both FGFs and FGF receptors simultaneously, facilitating of PGs on the physical characteristics of the culture sub- their interaction [ 301. It is known that at least three FGFs stratum, so caution must be used in extrapolating these - FGF-1, -2 and -5 - are expressed in the nervous sys- results to in vivo settings, Nonetheless, the distributions tem and exert trophic effects on several classes of neu- of some CSPGs are consistent with a ‘barrier’ function rons [31-34,35**]. Recently, Nurcombe et al. [35**] have in vivo (see above). For example, in the developing suggested that differences in the type of HS carried by a retina a receding wave of CS expression marks a front single core protein can render early neuroepithelial cells of centripetally directed axons, suggesting that axons selectively responsive either to FGF-1 or to FGF-2. This are guided by their avoidance of CS. Intriguingly, a CS- proposition is supported by evidence in other systems degrading enzyme disrupts the timing and direction of that HS structure can impart specificity to HSPG function retinofugal axons in the developing rat retina [50**]. (e.g. [36,37*,38,39*1).

PGs are involved in the assembly of ECM, and act as The kinetics of action of a family of protease inhibitors binding sites for molecules that associate with the ECM are dependent on PCs PGs bind virtually every major ECM component. In addi- The structurally related molecules antithrombin III, hep- tion, molecules such as growth factors (e.g. FGFs) and arin cofactor II, and protease nexin I all bind and inacti- enzymes (e.g. synaptic acetylcholinesterase) are often vate certain serine proteases (e.g. thrombin) much more immobilized in ECMs through interactions with HSPGs rapidly when appropriate GAGS are present. To a large [ 1,511. The importance of PGs in ECM structure and extent, GAGS act by simultaneously binding both pro- function is illustrated by a muscle cell line that is defec- tease and protease inhibitor, confining them to the same tive in GAG biosynthesis [52-l. This cell line produces an locality and thereby facilitating their interaction [38]. Of abnormal basal lamina and, probably as a consequence, interest to neurobiologists, protease nexin I is abundantly fails to form acetylcholine receptor clusters. The cells expressed in the CNS, and is thought to regulate neurite also fail to form such clusters in response to agrin, a outgrowth and neuronal migration [40]. GAG-binding ECM molecule that potently induces re- ceptor clusters on normal muscle cells, and is thought to be involved in synaptogenesis in zuko. Cell surface PCs participate in establishing cell-cell and cell-ECM contacts Although cell surface PGs can apparently be the sole receptors for attachment to certain substrata [37-l, PGs Conclusions usually facilitate interactions mediated through other re- ceptors, such as integrin-dependent cell attachment to Although much still needs to be learned about nervous ECM molecules [41], and neural cell adhesion molecule system PGs, the identities of many of the major species (NCAM)-dependent cell-cell adhesion [42,43]. A recent in the brain are now known. Tracking down the func- study suggests that cell surface HSPGs are especially im- tions of these molecules will probably not be easy. Their portant for the interaction of neural cells with fibronectin biological activities are likely to reside in their capacity [44*]. As ECM and cell adhesion molecules are thought to regulate, possibly in subtle ways, the functions of to provide important navigational cues to growing axons, the molecules they bind. Moreover, the repertoire of the involvement of PGs with such molecules suggests a molecules they bind will probably depend in part on the potential role for PGs in axon guidance. Recent studies precise structures of their GAG chains, structures which in insects support this idea [45**], defy easy analysis. Nevertheless, PGs are likely to continue to receive increasing attention in neurobiology, as their in viao distributions and in vitro activities suggest that ECM PCs regulate cell-cell and cell-matrix interactions they are widely involved in nervous system development The core protein of at least one PG, perlecan, supports and function. integrin-mediated cell attachment [ 461. In contrast, sev- eral PGs inhibit the biological activities of ECM and cell adhesion molecules, at least in vitro. For example, ad- sorbed CSPCs or CS/KSPGs can render culture substrata Acknowledgements inhospitable for neurite growth (24,251. Soluble CSPGs from rat brain also inhibit neurite outgrowth by ~Cl2 The author thanks ED Litwack and C Stipp for helpful comments cells [47]. Neurocan and the 3F8 CSPG of rat brain (but and assistance in preparing the manuscript. This work was supported not aggrecan) inhibit homophilic NCAM and neuron- hy NIH grant NS26862. Proteoglycans in the nervous system Lander 721

References and recommended reading teoglycans in Embryonic Chick Brain. J Biol Chem 1992, 267:12149-12161. One of only a few studies to look at PGs in the avian brain. Aggrecan Papers of particular interest, published within the annual period of and its mRNA are found to be transiently expressed in the emhtyonic review, have been highlighted as: chick brain. Unlike cartilage aggrecan, the brain form contains only CS . of special interest and not KS. Also detected in chick brain was a PG with a similar core . . of outstanding interest size, hut that can he distinguished from aggrecan by the presence of 1. Ruos~~tin E: Proteoglycans in CeU Regulation. J Biol Chem both CS and KS chains, reactivity with the HNK-1 monoclonal antibody, 1989, 264:1336+13372. and lack of developmental regulation.

2. BEKNFIELDM, KOKENYESI R, KA’~o M, HINKEZ MT, SPRING J, 15. FRYEKHJL, KELLYGM, MOUNARO L, HOCKFIELD, S: The High . GALLO RL, LOSE EJ: Biology of the Syndecans: a Family of . Molecular Weight Cat-301 Chondroitin Sulfate Proteoglycan Transmembrane Heparan Sulfate Proteoglycans. Annu Rez’ from Brain is Related to the Large Aggregating Proteoglycan Cell Biol 1992, 8~365-393. from Cartilage, Aggrecan. J Biol Chem 1992, 267:98749883. A cogent review that brings together historical, structural and functional The Cat-301 immunoreactive CSPG of brain is shown to have properties information about all members of the syndecan family, the major family similar to those of aggrecan. Also, authentic aggrecan from cartilage is of transmemhrane HSPGs. shown to react with Cat-301, as well as to another monoclonal antibody that recognizes the same brain PG as Cat-301. Nevertheless, the Cat-301 3. SHIEH MT, WUDLINN D, MONTGOMERYRI, ESKO JD, SPEAR PG: antigen can he distinguished from aggrecan by virtue of containing few, Ceil Surface Receptors for Herpes Simplex Virus Are Hep- if any, KS chains and having a lower buoyant density (indicative of a aran Sulfate Proteoglycans. .I Cell Biol 1992, 5:1272-1281. lower carbohydrate/protein ratio) than aggrecan. The data suggest that 4. IANDER AD, C.&OF AL:Extracellular Matrix in the Developing Cat-301 is either a modified form of aggrecan, or a new member of the Nervous System. In Molecular Genetics of Nertjous Sy.stem aggrecan family. Tumors. Edited by Levine AJ, Schmidek HH. New York: Wiley~ Iiss; 1993:341-355. 16. IWATA M, CA~&SON S: A Large Chondroitin Sulfate Proteogly- . . can Has the Characteristics of a General Extracellular Ma- 5. KLINGERMM, MARGOLISRU, MARCOUSRK: Isolation and Char- trix Component of Adult Brain. J Neurosci 1993, 13:195-207. acterization of the Heparan S&ate Proteoglycans of Brain. 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Using immunohistochemistty, the antigen Was Cell Rio1 1990, 111:3177~3188. detected around cerehellar Purkinje cells, Golgi cells and deep cerehel- lar neurons, as well as in brainstem nuclei that project mossy fibers to 12. RArlCH LJ,KAFXHIK?ZYAh' L, MAUKEL P, MAKCx)LISRU, MARGOUS the cerebellum. Transient immunoreactivity wa$ also found on ponto- . . RK: Cloning and Primary Structure of Neurocan, a Devel- cerehebr fibers during development. opmentally Regulated, Aggretating Chondroitin Sulfate Pro- teoglycan of Brain. J Biol Chem 1992, 267:1953619547. 20. ZAREMBA S, NAEXX~ J, BARNST~LE C, HOCKFIEI~ S: Neuro- The cloning of neurocan is described The cDNA that was obtained ens naI Subsets Express Multiple High-Molecular-Weight Cell- codes a protein similar to aggrecan and versican, including an amino Surface Glyconjugates Defined by MonoclonaI Antibodies terminal hyaluronate binding domain, and carbOx)-terminal epidermal Cat-301 and VCl.1. J Neurosci 1990, 10:2985-2995. growth factor (EGF)-like, -like and complement regulatory-like do- mains. Evidence is presented that the adult brain contains only a trunk 21. FI~ITA SC, TAUA Y, M~RAK~~I F, HAYGHI M, MATSUMIJRAM: cated form of neurocan, lacking the amino-terminal region. Glycosaminoglycan-Related Epitopes Surrounding Different Subsets of Mammalian Central Neurons. Neurosci Res 1989, 13. PE~UDESG, RAHEMTL!I_LAF, LANE WS, AS!IER RA, BIGN~II A: 7:117-130. . Isolation of a Large Aggregating Proteoglycan from Human Brain. J Bid Chem 1992, 267:23883-23887. 22. RI:KTOLOTTOA, RO~CA G, CANAVESFG, MIGH~U A, SCHIFFERD: Versican is isolated from human brain and shown to bind hyaluronic Chondroitin Sulfate Proteoglycan Surrounds a Subset of HU- acid. The relationship of versican to GHAP @aI hyaluronic acid hind- man and Rat CNS Neurons. .I Neurosci k’e.5 1991, 29:225-234. ing protein) is also discussed. GHAP, a previously characterized protein, 23. 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24. SNOW DM, LEMMON V, CARRI~VODA, CAPIAN Al, SILVER J: Sul- 3’. SANIXRSON RD, SNEEI) TB, YOLING IA, S~ILLI~AV GL, L~NUEHAD: fated Proteoglycans in AstrogliaI Barriers Inhibit Neurite . Adhesion of B Lymphoid (MPC-11) Cells to Type I CoUa- Outgrowth in Vitro. Exp New-01 1990, 109:111-130. gen is Mediated by the Integral Membrane Proteoglycan, Syndecan. J Immwzol 1992, 148:3902-3911. 25. SNOW DM, WATANARE M, LETOI:RNFAIJ PC, SIL~XR J: A Chon- This study demonstrates that a ceil surface HSPG can directly mediate droitin Sulfate Proteoglycan May Influence the Direction cell adhesion, and that a single HSPG can have different affinities for of Retinal Ganglion Cell Outgrowth. Detelopmerzf 1991. an ECM l&and, depending, presumably, on the structure of its GAG 113:147%1485. chains.

26. HALFTER W: A Heparan Sulfate Proteoglycan in Developing 38. OLSON ST, BJORK I: Role of Protein Conformational Changes, . . Avian Axonal Tracts. J Neurosci 1993, 13:2863-2873. Surface Approximation and Protein Cofactors in Heparin- A search for monochal antibodies againsr retinal basal lamina and op- Accelerated Antithrombin-Proteinase Reactions. In Heparin tic nerve turns up four antibodies that recognize a single, large HSPG. and Related Po&accharides. Edited by Lane DA. New York: Although this molecule exhibits biochemical properties similar to those Plenum Press; 1992:155-165. of perlecan, its expression in CNS fiber tracts indicates that is not iden tical to perlecan. Until this report, it was not clear that any HSPGs were 39. SAN ANTONIO JD, SUIVER J, L%~ZEKJ, ~OVSK?’ MJ, L&NOCR present in the ECM of the brain. Interestingly, like several other ECM . AD: Specificity in the Interactions of ExtraceUular Matrix molecules (e.g. laminin and tibronectin), expression of this PG m the Proteins with Subpopulations of the Glycosaminoglycan parenchyma of the brain appears to be transient. Heparin. Biochmistg~ 1993, 32:4746-4755. A direct demonstration that some ECM molecules (e.g. laminin, fi 27. SCRANTON TW, IwATA M, CARLSON SS: The SV2 Protein of bronecrin and type I collagen) can bind preferentially to subpop- . . Synaptic Vesicles Is a Keratan Sulfate Proteoglycan. J Neu- ularions of the GAG heparin. The implication is that features in the rochem 1993, 61:2%44. sfructure of heparin!HS determme binding specificiv. Thus, carbohy~ An important clarification of a complicated story. ‘Two’ synaptic vesicle drdte structure is likely to regulate the functions of HSPGs. molecules, a large PG and a major vesicle called SV2 are 40. LINDNEKJ, G~IENTHERJ, NICK H, ZINSER G, ANTONICEK H, shown to be forms of the same integral membrane protein, bearing SHACHNER M, MONARD D: Modulation of Granule Cell Mi- either long or short KS chains. This helps to bring together findings gration by a Glia-Derived Protein. Proc Natl Acad Sci L’SA in other labs that the synaptic vesicle PG is involved in acetylcholine 1986. 83:4568+571. transport, and that the SV2 protein is evolutionarily related fo bacterial transport proteins. .*I. WOOL% A, COI’CI~UN JR: Heparan Sulphate Proteoglycans and Signalling in CeU Adhesion. In Ifeparin and Related 28. YAYONA, K~AGSBRIIN M, ESKO JD, LEDER P, ORNITZ, DM: Cell Po!ysaccharide.s. Edited hy lane DA. New York: Plenum Press; Surface, Heparin-like Molecules are Required for Binding 1992:X7-96. of Basic Fibroblast Growth Factor to its High Affinity Re- ceptor. Cell 1991, 64:841-848. 42. COLE GJ, LOELX?! A, GILDER L: NeuronaI CeU-CeU Adhe- sion Depends on Interactions of N-CAM with Heparin-Like 29. RAI%AECER AC, KRUFKAA, 01,~~ BB: Requirement of Heparan Molecules. Nutwe 1986, 320:445447. Sulfate for bFGF-Mediated Fibroblast Growth and Myoblast Differentiation. Science 1991, 252:1705-1708. 33. REYEX AA, AKES~N R, BREZINA L, C01.e GJ: Structural Require- ments for Neural CeU Adhesion Molecule-Heparin Interac- 30. KAN M, WANG F, XI’ J, CRNIR JW, Hall J, MCKEE~ WL An tion. Cc/I Regul 1990, 1~5677576. Essential Heparin-Binding Domain in the Fibroblast Growth ‘t+. HAI’c;EN PK, LETO~~RNEAUPC, DRAKt SI., FIIRCKr LT, MCCARTHY Factor Receptor KInase. Science 1993, 259:191%1921. . JB: A Cell-Surface Heparan Sulfate Ptoteoglycan Mediates 31. WALICKEP: Basic and Acidic Fibroblast Growth Factors Have Neural CeU Adhesion and Spreading on a Defined Sequence Trophic Effects on Neurons from Multiple CNS Regions. J from the C-Terminal CeU and Heparin Binding Domain of Neurosci 1988, 8:261%2627. Fibronectin, FN-C/H IL ,/ NeMrosci 1992, 12:2597F2608. Enzymatic removal of HS from rat neuroblastoma cells inhibited their 32 ELDE R, CAO Y, CINTRAA, BKEI.JFTC, PELTO HUIKKO M, J~NTTIIA attachment and spreading on Iibronectin fragments and peptides, as did T, FUXE K, PETTERSSON RF, HOKFELT T: Prominent Expression antibodies directed against a mouse melanoma HSPG. of Acidic Fibroblast Growth Factor in Motor and Sensory Neurons. Neuron 1991, 7:34‘+364. 45. WANG L, Dl:NBI:Rci J. A Role for Proteoglycans in the Guid- . . ante of a Subset of Pioneer Axons in Cultured Embryos of 33. GOMEZ-PINILLA F, LEE JWK, COT~~ANCW: Basic FGF in Adult the Cockroach. Neuron 1992, 8:701-714. Rat Brain: Cellular Distribution and Response to Entorhi- Axons in the developing insect nenvus system follow highly sterro nal Lesion and Fimbria-Fornix Transection. J Nertrosci 1992, typed pathways. Llsing a semi-in z’itro system, evidence was found that 12:345-355. heparin and HS specifically perturb certain axon guidance decisions. Similar perturbations were produced by two HS degrading enzymes. 34. HLIGHES RA, SENDTNER M, G~LOPAKD M, LINDHOIM D, THOENEN H: Evidence that Fibroblast Growth Factor 5 is a Ma- 4. HAUSHI K, MADRIJA, YIIRCHENCO PD: EndotheliaI CeUs Inter- jot Muscle-Derived Survival Factor for Cultured Spinal act with the Core Protein of Basement Membrane Perlecan Motoneurona Neuron 1993, 10:36%377. through 01 and 03 Integrins: an Adhesion Modulated by Glycosaminoglycan. J Cell Rio1 1992, 119:945-959. 35. NIJRCOMBE V, FORD MD, WILDSCHIITJA, BAKLETTPF: Develop- . . mental Regulation of Neural Response to FGF-1 and FGF-2 47. OOIIIRA A, MATSLIIF, KATOH-SEMBAR: Inhibitory Effects of by Heparan Sulfate Proteoglycan. Science 1993, 260:103-106. Brain Chondroitin Sulfate Proteoglycans on Neurite Out- In this provocative study, an HSPG was isolated from mouse neuron growth from PC12D Cells. ,I Neurosci 1991, 11822-827. epithelial cells at two stages of development, and tested for binding 48. GRUME?’ M, I’LACCLIS A, MARCOUS RL:: Functional Characteri- to FGF-1 and FGF~2. HSPG from embtyonic day 9 cells preferentialb . zation of Chondroitin Sulfate Proteoglytcans of Brain: Inter- bound FGF-2, whereas HSPG from day 11 cells preferentially bound actions with Neurons and Neural CeU Adhesion Molecules. FGF~l. Similar speciIicity was seen in the ability of the HSPG samples ,I Cell Bioi 1993, 120:815-824. to potentiate the actions of FGF-1 and FGF-2. The developmental switch Evidence is presented that the brain CSPGs neurocan ( 1Dl) and 3F8 ins in binding coincides with a switch in expression of FGFs in the neuro- hihit homophilic NCAIv-NCAh4 and NgCAWNgCAM binding (whereas epithelium, from FGF-2 to FGF~l, over the same period. aarecan does so poorly), and that neurons exhibit some ability to at tach to the core proteins of these PGs. 36. SALhlfilRTA M, EI~NIL:S K, VAINIO S, HOFER LJ, CHIQuEI’ EHRlSMANN R, THESLEFF I, JALKANEN M: Syndecan from Em- 19. MUIR D, EN(;YALLE, VARON 5. .MANTIIORIJEM: Schwannoma bryonic Tooth Mesenchyme Binds Tenascin. J Biol @em Cell-Derived Inhibitor of the Neurite-Promoting Activity of l%‘l, 26617733-7739. Laminin. I C&l Rio1 1989. 109:2353-2362. Proteoglycans in the nervous system Lander 723

50. BRI~TIS PA, CANNING DR, Sll.VERJ: Chondroitin Sulfate as a Nerve-Induced but Not Spontaneous Clusters of the Acetyl- . . Regulator of Neural Patterning in the Retina. Science 1992, choline Receptor and the 43 kDa Protein. ,I ,%xwosci 1993, 255~733-736. 13:586595. This paper raises the provocative hypothesis that the disappearance of Acrtylcholine receptor clustering by muscle cells is an important model CS from the developing mammalian retina sets up a spatial gradient for early steps in synaptogenesis. In this paper, S27, a variant of C2 that guides ganglion cell axons toward the optic nerve head. Preti~ mouse myoblasts that is deficient in GAG biosynthesis, is described, Un~ ous in uitro studies had suggested that CS repels retinal axons. In like the parent line, 527 cells fail to form spontaneous or agrin-induced this study, evidence is presented that newly differentiating ganglion acetylcholine receptor clusters. In addition, basal lamina components cells find themselves within a steep CS gradient oriented away from (e.g. Iaminin) are also reduced on the surface of these cells. Interest- the optic disk. Evidence is also presented that exposure of developing ingly, S27 cells are capable of forming acetylcholine receptor clusters retinas to a CS-degrading enzyme causes large perturbations in ganglion at sites of contact by neuronal processes. Possible explanations for the cell axon guidance, as well as causing ectopic differentiation of ganglion different responses of these cells to clustering signals are discussed. cells. 53 GAUAGHERJT: The Extended Family of Proteoglycans: Social 51. BRANDANE, MALLWNAWJ M, GARK~DOJ, INESTROSA N: Anchor- Residents of the PericeIIular Zone. Curr Opin Cell Bioll989, age of Collagen-Tailed Acetylchohnesterase to the Extracel- 1:1201~1218. IuIar Matrix Is Mediated by Heparan Sulfate Proteoglycans. J Cell Biol 1985, 101:9855992. AD Lander, Department of Brain and Cognitive Sciences, E25-435, Mas- 52. GARDEN H, LLJPA M, BOWN D, HAU. Z: A Muscle Ceil sachusetts Institute of Technology, Cambridge, MaSSKhUSettS 02139, . Variant Defective in Glycosaminoglycan Biosynthesis Forms I’SA.