Developmentally regulated expression of brain-specific chondroitin sulfate proteoglycans, neurocan and phosphacan, in the postnatal rat hippocampus

Developmental changes in the distribution of brain-specific chondroitin sulfate proteoglycans, neurocan and phosphacan/RPTPzeta/beta, in the hippocampus of the Sprague-Dawley rat were examined using monoclonal antibodies 1G2 and 6B4. The 1G2 immunoreactivity was predominant in the neonatal hippocampus while the 6B4 immunoreactivity was predominant in the mature hippocampus. Moderate 1G2 immunoreactivity was detected in the dentate gyrus and subiculum immediately after birth. Immunoreactivity reached a peak on postnatal days 7-10 (P7-P10) when intense 1G2 labeling was present throughout the neuropil layers of the hippocampus except the mossy fiber tract. 6B4 immunoreactivity was limited in the stratum lacunosum moleculare of CA1 in the neonatal hippocampus. It gradually increased by P21 when diffuse 6B4 immunoreactivity was detected in the stratum oriens and radiatum of Ammon's horn, and in the hilus and inner one-third molecular layer of the dentate gyrus, while 1G2 immunoreactivity decreased after P21. In the adult hippocampus, moderate 6B4 immunoreactivity was present in the stratum oriens and radiatum of Ammon's horn, and in the hilus and inner one-third molecular layer of the dentate gyrus, but not in the mossy fiber tract. In addition, strong 6B4 labeling appeared around a subset of neurons after P21. The results suggest that neurocan may have a role in the development of neuronal organization, while phosphacan/RPTPzeta/beta may contribute to the maintenance and plasticity of synaptic structure and function. Furthermore, the absence of 1G2 and 6B4 immunoreactivities in the stratum lucidum suggests that neurocan and phosphacan/RPTPzeta/beta may function as a barrier for the extension of mossy fibers and provide an environment permissive for fasciculation of the mossy fibers.

Overlapping functions of the cell adhesion molecules Nr-CAM and L1 in cerebellar granule cell development

The structurally related cell adhesion molecules L1 and Nr-CAM have overlapping expression patterns in cerebellar granule cells. Here we analyzed their involvement in granule cell development using mutant mice. Nr-CAM-deficient cerebellar granule cells failed to extend neurites in vitro on contactin, a known ligand for Nr-CAM expressed in the cerebellum, confirming that these mice are functionally null for Nr-CAM. In vivo, Nr-CAM-null cerebella did not exhibit obvious histological defects, although a mild size reduction of several lobes was observed, most notably lobes IV and V in the vermis. Mice deficient for both L1 and Nr-CAM exhibited severe cerebellar folial defects and a reduction in the thickness of the inner granule cell layer. Additionally, anti-L1 antibodies specifically disrupted survival and maintenance of Nr-CAM-deficient granule cells in cerebellar cultures treated with antibodies. The combined results indicate that Nr-CAM and L1 play a role in cerebellar granule cell development, and suggest that closely related molecules in the L1 family have overlapping functions.

Soluble forms of NCAM and F3 neuronal cell adhesion molecules promote Schwann cell migration: identification of protein tyrosine phosphatases zeta/beta as the putative F3 receptors on Schwann cells

Neural cell adhesion molecule (NCAM) and F3 are both axonal adhesion molecules which display homophilic (NCAM) or heterophilic (NCAM, F3) binding activities and participate in bidirectional exchange of information between neurones and glial cells. Engineered Fc chimeric molecules are fusion proteins that contain the extracellular part of NCAM or F3 and the Fc region of human IgG1. Here, we investigated the effect of NCAM-Fc and F3-Fc chimeras on Schwann cell (SC) migration. Binding sites were identified at the surface of cultured SCs by chimera coated fluorospheres. The functional effect of NCAM-Fc and F3-Fc binding was studied in two different SC migration models. In the first, migration is monitored at specific time intervals inside a 1-mm gap produced in a monolayer culture of SCs. In the second, SCs from a dorsal root ganglion explant migrate on a sciatic nerve cryosection. In both systems addition of the chimeras significantly increased the extent of SC migration and this effect could be prevented by the corresponding anti-NCAM or anti-F3 blocking antibodies. Furthermore, antiproteoglycan-type protein tyrosine phosphatase zeta/beta (RPTPzeta/beta) antibodies identified the presence of RPTPzeta/beta on SCs and prevented the enhancing effect of soluble F3 on SC motility by 95%. The F3-Fc coated Sepharose beads precipitated RPTPzeta/beta from SC lysates. Altogether these data point to RPTPzeta/beta is the putative F3 receptor on SCs. These results identify F3 and NCAM receptors on SC as potential mediators of signalling occurring between axons and glial cells during peripheral nerve development and regeneration.

Inhibitory effects of neurocan and phosphacan on neurite outgrowth from retinal ganglion cells in culture

PURPOSE

Neurocan and phosphacan are nervous tissue-specific chondroitin sulfate proteoglycans (CSPGs) that are highly expressed in postnatal rat retina. To elucidate potential roles of neurocan and phosphacan on neurite outgrowth from retinal ganglion cells (RGCs), in vitro experiments were conducted with purified RGCs.

METHODS

Neurocan and phosphacan were purified from postnatal rat brain by DEAE-column chromatography and subsequent gel chromatography. RGCs were obtained from postnatal rat retinas by a two-step immunopanning procedure using an anti-Thy 1,1 antibody and an anti-macrophage antibody. Neurite outgrowth from RGCs was examined on poly-L-lysine (PLL)-conditioned plates, and PLL-conditioned plates treated with neurocan or phosphacan.

RESULTS

Compared with PLL-conditioned plates, neurocan and phosphacan inhibited neurite outgrowth from RGCs at 48 and 72 hours after seeding. When chondroitin sulfate side chains linked to the core proteins were digested by chondroitinase ABC, the inhibitory effect remained, indicating that the core proteins are related to the effect. Furthermore, the digestion of chondroitin sulfate side chains linked to phosphacan core protein significantly promoted the inhibitory effect of phosphacan on neurite outgrowth from RGCs.

CONCLUSIONS

Neurocan and phosphacan, which are highly expressed in postnatal rat retina, inhibit neurite outgrowth from postnatal rat RGCs, indicating that these proteoglycans may be inhibitory factors against neurite outgrowth from RGCs during retinal development.

Identification of GIT1/Cat-1 as a substrate molecule of protein tyrosine phosphatase zeta /beta by the yeast substrate-trapping system

We used a genetic method, the yeast substrate-trapping system, to identify substrates for protein tyrosine phosphatases zeta (PTPzeta/RPTPbeta). This method is based on the yeast two-hybrid system, with two essential modifications: conditional expression of protein tyrosine kinase v-src (active src) to tyrosine-phosphorylate the prey proteins and screening by using a substrate-trap mutant of PTPzeta (PTPzeta-D1902A) as bait. By using this system, several substrate candidates for PTPzeta were isolated. Among them, GIT1/Cat-1 (G protein-coupled receptor kinase-interactor 1/Cool-associated, tyrosine-phosphorylated 1) was examined further. GIT1/Cat-1 bound to PTPzeta-D1902A dependent on the substrate tyrosine phosphorylation. Tyrosine-phosphorylated GIT1/Cat-1 was dephosphorylated by PTPzeta in vitro. Immunoprecipitation experiments indicated that PTPzeta-D1902A and GIT1/Cat-1 form a stable complex also in mammalian cells. Immunohistochemical analyses revealed that PTPzeta and GIT1/Cat-1 were colocalized in the processes of pyramidal cells in the hippocampus and neocortex in rat brain. Subcellular colocalization was further verified in the growth cones of mossy fibers from pontine explants and in the ruffling membranes and processes of B103 neuroblastoma cells. Moreover, pleiotrophin, a ligand for PTPzeta, increased tyrosine phosphorylation of GIT1/Cat-1 in B103 cells. All these results indicate that GIT1/Cat-1 is a substrate molecule of PTPzeta.

Recombinant core protein fragment of phosphacan, a brain specific chondroitin sulfate proteoglycan, promote excitotoxic cell death of cultured rat hippocampal neurons

We investigated the role of phosphacan, a chondroitin sulfate proteoglycan that is constitutively expressed in the adult hippocampus, and recombinant core proteins of phosphacan in excitotoxic cell death of primary cultured rat hippocampal neurons. Phosphacan had no significant effect on excitotoxic neuronal death. Surprisingly, one of three recombinant proteins corresponding to N-terminal portions of phosphacan core protein dramatically promoted excitotoxic neuronal death. Moreover, the recombinant protein induced cell death of rat hippocampal neurons, even when neurons were not exposed to glutamate. These results suggest that proteolytic degradation of phosphacan and resultant core protein fragments may contribute to neuronal degeneration of hippocampal neurons in various neuropathological conditions.

Haptotactic migration induced by midkine. Involvement of protein-tyrosine phosphatase zeta. Mitogen-activated protein kinase, and phosphatidylinositol 3-kinase

Midkine, a heparin-binding growth factor, plays a critical role in cell migration causing suppression of neointima formation in midkine-deficient mice. Here we have determined the molecules essential for midkine-induced migration. Midkine induced haptotaxis of osteoblast-like cells, which was abrogated by the soluble form of midkine or pleiotrophin, a midkine-homologous protein. Chondroitin sulfate B, E, chondroitinase ABC, B, and orthovanadate, an inhibitor of protein-tyrosine phosphatase, suppressed the migration. Supporting these data, the cells examined expressed PTPzeta, a receptor-type protein-tyrosine phosphatase that exhibits high affinity to both midkine and pleiotrophin and harbors chondroitin sulfate chains. Furthermore, strong synergism between midkine and platelet-derived growth factor in migration was detected. The use of specific inhibitors demonstrated that mitogen-activated protein (MAP) kinase and protein-tyrosine phosphatase were involved in midkine-induced haptotaxis but not PDGF-induced chemotaxis, whereas phosphatidylinositol 3 (PI3)-kinase and protein kinase C were involved in both functions. Midkine activated both PI3-kinase and MAP kinases, the latter activation was blocked by a PI3-kinase inhibitor. Midkine further recruited PTPzeta and PI3-kinase. These results indicate that PTPzeta and concerted signaling involving PI3-kinase and MAP kinase are required for midkine-induced migration and demonstrate for the first time the synergism between midkine and platelet-derived growth factor in cell migration.

Receptor-like protein tyrosine phosphatase gamma (RPTPgamma), but not PTPzeta/RPTPbeta, inhibits nerve-growth-factor-induced neurite outgrowth in PC12D cells

Receptor-like protein tyrosine phosphatase gamma (RPTPgamma) and PTPzeta/RPTPbeta are RPTPs which structurally resemble each other and form a distinct RPTP family. Both molecules are highly expressed in the central nervous system (CNS), though RPTPgamma is distributed also in several peripheral tissues. To date, the functional differences between RPTPgamma and PTPzeta in neuronal cells have not been made clear because their substrate and ligand molecules have not been fully elucidated. To address this issue, we established PC12D cell transfectants stably expressing rat RPTPgamma or PTPzeta and analyzed the effects on cellular response to nerve growth factor (NGF). Compared with the parent PC12D cells which extend neurites vigorously in response to NGF, the transfectants expressing RPTPgamma showed almost no neurite outgrowth. In contrast, neurite extension in PTPzeta-expressing clones on NGF treatment was the same as in parent cells. We investigated differences in tyrosine phosphorylation levels in the cellular proteins in these cells after the NGF treatment before morphological charges appeared. Despite the lack of a response, major proteins and MAP kinase in RPTPgamma-expressing PC12D cells displayed normal tyrosine phosphorylation changes on NGF treatment. However, tyrosine phosphorylation levels in the protein components purified with p13(suc1) agarose (p13(suc1) complex) from RPTPgamma-expressing cells were different from those of the control cells. (1) Tyrosine-phosphorylation levels of 140- and 117-kD proteins were significantly reduced. (2) Rapid tyrosine phosphorylation of 58-kD protein induced by NGF was absent. (3) Activities of tyrosine kinases and protein kinase C in the p13(suc1) complex were markedly reduced. We found that the p13(suc1) complex also contained cytoskeletal proteins such as MAP2 and neurofilaments, but their phosphorylation levels were not different. These results indicate that RPTPgamma and PTPzeta have different substrate specificities, and RPTPgamma inhibits NGF-induced neurite outgrowth of PC12D cells through modulation of the p13(suc1) complex.

Expression of brain specific chondroitin sulfate proteoglycans, neurocan and phosphacan, in the developing and adult hippocampus of Ihara's epileptic rats

Ihara's epileptic rats (IER) is an animal model of temporal lobe epilepsy with mycrodysgenesis, that exhibit abnormal migration of hippocampal neurons and recurrent spontaneous seizures. As an attempt to elucidate the roles of extracellular matrix molecules in the epileptogenecity and mossy fiber sprouting, immunohistochemical localization of brain specific chondroitin sulfate proteoglycans (CSPGs), neurocan and phosphacan, was examined in the hippocampus of postnatal IER and Sprague-Dawley (SD) rats using monoclonal antibodies 1G2 against neurocan and 6B4 against phosphacan. There was no difference in the expression of these two CSPGs between IER and SD rats in the 1st postnatal week. However, the expression of neurocan was poor in the hippocampus of IER in the 2nd and 3rd weeks whereas intense labeling of neurocan was present throughout the hippocampus of SD rats. Labeling of neurocan was almost absent in the hippocampus, while phosphacan was diffusely expressed in the stratum oriens and radiatum of Ammon's horn, and in the hilus and inner one-third molecular layer of the dentate gyrus at the 2nd month after birth. There was no difference in the expression of neurocan and phosphacan between IER and SD rats at the 2nd month after birth. By contrast, phosphacan was reduced in the inner molecular layer of the dentate gyrus in 8-month-old IER, while neurocan was reexpressed in the outer molecular layer and hilus in 3- and 8-month-old IER. It was suggested that the insufficient expression of neurocan may affect the development of neuronal organization in the hippocampus, and that the remodeling of extracellular matrix in the dentate gyrus may contribute to the mossy fiber sprouting into the inner molecular layer.

Inhibitory proteoglycan immunoreactivity is higher at the caudal than the rostral Schwann cell graft-transected spinal cord interface

To begin to evaluate the influence that proteoglycans may have on the success of Schwann cell (SC) transplants to induce axonal regrowth across a complete transection lesion and beyond, we determined the pattern of expression of inhibitory chondroitin sulfate proteoglycans (CSPGs) 3 weeks after transplantation into completely transected adult rat thoracic spinal cord. Using immunohistochemistry, we observed that: (1) CSPGs recognized by CS-56 antibody are present on astrocytes, fibroblasts, and SCs in the distal graft, and at lesion and cystic cavity borders; (2) CS-56 immunoreactivity (IR) is greater at the caudal SC graft-host cord interface than the rostral interface; (3) phosphacan-IR, also greater at the caudal interface, is associated with astrocytes, fibroblasts, as yet unidentified cells, and extracellular matrix; (4) neurocan-IR is present on astrocytes and as yet unidentified cells in grey and white matter; and (5) NG2-IR is associated with matrix near SC grafts, unidentified cells mainly in white matter, and lesion borders and cysts. Neither oligodendrocytes nor activated macrophages/microglia were immunostained. In sum, the CSPGs studied are increased at 3 weeks, especially at the caudal SC graft-cord interface, possibly contributing to an inhibitory molecular barrier that precludes regrowing descending axons from entering the caudal host cord.

Glial tumor cell adhesion is mediated by binding of the FNIII domain of receptor protein tyrosine phosphatase beta (RPTPbeta) to tenascin C

The extracellular domain of receptor protein tyrosine phosphatase beta (RPTPbeta) is composed of several domains which mediate its interactions with distinct ligands present on the surface of either neurons or glial cells. Here, we demonstrate that the fibronectin type III domain (FNIII) of RPTPbeta binds to glial tumor-derived cell lines and primary astrocytes. We used affinity purification to isolate several proteins that specifically bind to the FNIII domain of RPTPbeta. One of these, a 240 kDa protein that was purified from U118MG glioblastoma cell, was identified as tenascin C based on the amino acid sequence of several tryptic peptides. The interaction of RPTPbeta with tenascin C was found to mediate cell adhesion. Adhesion and spreading of SF763T astrocytoma cells expressing RPTPbeta on tenascin C was specifically abolished by the addition of a soluble fragment containing the FNIII domain of the receptor. RPTPbeta-dependent cell adhesion was mediated by binding to the alternatively spliced FNIII repeats A1,2,4 (TnfnA1,2,4) of tenascin C. Furthermore, COS cells expressing RPTPbeta adhere to TnfnA1,2,4, while the parental cells did not. These results demonstrate that the FNIII domain of RPTPbeta binds to tenascin C and suggest that RPTPbeta present on glial tumor cells is a primary adhesion receptor system to the extracellular matrix.

Multiple variants of receptor-type protein tyrosine phosphatase beta are expressed in the central nervous system of Xenopus

We have isolated cDNA clones encoding the Xenopus homologue of receptor-type protein tyrosine phosphatase beta (RPTPbeta), and identified 13 forms of the mRNA provably generated by alternative splicing. All the conceptual translates have a carbonic anhydrase-like domain, a fibronectin type III-like repeat and a spacer in the extracellular segment. Eleven of them (designated XRPTPbeta.1-XRPTPbeta.11) also have highly conserved two intracellular PTP domains, whereas the other two variants (sXRPTPbeta.1 and sXRPTPbeta.2) have neither transmembrane nor cytoplasmic segment. There are five peptides that can be inserted in various combinations into the spacer region. Northern and Western blot analyses show central nervous system-specific expression of the XRPTPbeta mRNAs and proteins. Chondroitinase ABC treatment of the brain and spinal cord extracts results in separation of six protein bands on the Western blot, in association with a decrease in the size of major bands, indicating that the major XRPTPbeta variants are chondroitin sulfate proteoglycans. The results of these as well as reverse-transcribed polymerase chain reaction analyses suggest that the amounts of different XRPTPbeta variants are regulated in tissue- and developmental stage-specific manners.

Postnatal development of perineuronal nets in wild-type mice and in a mutant deficient in tenascin-R

The extracellular matrix glycoprotein tenascin-R (TN-R), colocalizing with hyaluronan, phosphacan, and aggregating chondroitin sulphate proteoglycans in the white and grey matter, is accumulated in perineuronal nets that surround different types of neurons in many brain regions. To characterize the role of TN-R in the formation of perineuronal nets, we studied their postnatal development in wild-type mice and in a TN-R knock-out mutant by using the lectin Wisteria floribunda agglutinin and an antibody to nonspecified chondroitin sulphate proteoglycans as established cytochemical markers. We detected the matrix components TN-R, hyaluronan, phosphacan, neurocan, and brevican in the perineuronal nets of cortical and subcortical regions. In wild-type mice, lectin-stained, immature perineuronal nets were first seen on postnatal day 4 in the brainstem and on day 14 in the cerebral cortex. The staining intensity of these nets for TN-R, hyaluronan, phosphacan, neurocan, and brevican was extremely weak or not distinguishable from that of the surrounding neuropil. However, all markers showed an increase in staining intensity of perineuronal nets reaching maximal levels between postnatal days 21 and 40. In TN-R-deficient animals, the perineuronal nets tended to show a granular component within their lattice-like structure at early stages of development. Additionally, the staining intensity in perineuronal nets was reduced for brevican, extremely low for hyaluronan and neurocan, and virtually no immunoreactivity was detectable for phosphacan. The granular configuration of perineuronal nets became more predominant with advancing age of the mutant animals, indicating the continued abnormal aggregation of chondroitin sulphate proteoglycans complexed with hyaluronan. As shown by electron microscopy in the cerebral cortex, the disruption of perineuronal nets was not accompanied by apparent changes in the synaptic structure on net-bearing neurons. The regional distribution patterns and the temporal course of development of perineuronal nets were not obviously changed in the mutant. We conclude that the lack of TN-R initially and continuously disturbs the molecular scaffolding of extracellular matrix components in perineuronal nets. This may interfere with the development of the specific micromilieu of the ensheathed neurons and adjacent glial cells and may also permanently change their functional properties.

Correlation of anti-idiotype network with survival following anti-G(D2) monoclonal antibody 3F8 therapy of stage 4 neuroblastoma

BACKGROUND

A transient human anti-mouse antibody response was associated with significantly longer survival [Cheung et al. (1998): J Clin Oncol 16:3053] following antibody 3F8 (Ab1) treatment. We postulate that the induction of an idiotype network which included anti-anti-idiotypic (Ab3) and anti-G(D2) (Ab3') responses is associated with tumor control.

PROCEDURE

Thirty-four patients with stage 4 neuroblastoma (NB) diagnosed at > 1 year of age were treated with anti-G(D2) monoclonal antibody 3F8 at the end of chemotherapy

RESULTS

Long-term progression-free survival and overall survival correlated significantly with Ab3' andAb3, but not with non-idiotypic antibody responses. Only one of six individual specificities showed significant correlations with patient survival.

CONCLUSIONS

As in vitro correlates of idiotype network initiated by Ab1 treatment, Ab3 and Ab3' may provide convenient biologic endpoints for monoclonal antibody therapy of advanced NB, and a rationale for choosing specific anti-idiotypic antibodies for vaccine development.

Contactin-associated protein (Caspr) and contactin form a complex that is targeted to the paranodal junctions during myelination

Specialized paranodal junctions form between the axon and the closely apposed paranodal loops of myelinating glia. They are interposed between sodium channels at the nodes of Ranvier and potassium channels in the juxtaparanodal regions; their precise function and molecular composition have been elusive. We previously reported that Caspr (contactin-associated protein) is a major axonal constituent of these junctions (Einheber et al., 1997). We now report that contactin colocalizes and forms a cis complex with Caspr in the paranodes and juxtamesaxon. These proteins coextract and coprecipitate from neurons, myelinating cultures, and myelin preparations enriched in junctional markers; they fractionate on sucrose gradients as a high-molecular-weight complex, suggesting that other proteins may also be associated with this complex. Neurons express two contactin isoforms that differ in their extent of glycosylation: a lower-molecular-weight phosphatidylinositol phospholipase C (PI-PLC)-resistant form is associated specifically with Caspr in the paranodes, whereas a higher-molecular-weight form of contactin, not associated with Caspr, is present in central nodes of Ranvier. These results suggest that the targeting of contactin to different axonal domains may be determined, in part, via its association with Caspr. Treatment of myelinating cocultures of Schwann cells and neurons with RPTPbeta-Fc, a soluble construct containing the carbonic anhydrase domain of the receptor protein tyrosine phosphatase beta (RPTPbeta), a potential glial receptor for contactin, blocks the localization of the Caspr/contactin complex to the paranodes. These results strongly suggest that a preformed complex of Caspr and contactin is targeted to the paranodal junctions via extracellular interactions with myelinating glia.

Expression of receptor tyrosine phosphatase gamma during early development of the chick embryo

Studies in Drosophila suggest that receptor-tyrosine phosphatases are key regulators of neural development, however little is known about their expression or function in the nervous system of vertebrate embryos. In this report, we describe the expression pattern of RPTPgamma during early chick embryogenesis. Transcripts are largely restricted to the developing nervous system including oculomotor, trochlear and branchiomotor populations but are absent from spinal motor neurones. RPTPgamma is also detected in cells in the positions of hindbrain reticulospinal neurones, spinal commisural neurones and in cells with neuronal morphology in the ventral diencephalon. Within the peripheral nervous system transcripts are found in neuroblasts delaminating from epibranchial placodes and subsequently in placode-derived cranial ganglia. Outside the nervous system expression is detected in somites and transiently in the second branchial arch and the cranial mesenchyme.

Expression of receptor protein tyrosine phosphatases in embryonic chick spinal cord

Receptor-like protein tyrosine phosphatases potentially play a crucial role in axon growth and targeting. We focus here on their role within the embryonic avian spinal cord, in particular the development and outgrowth of motorneurons. We have used in situ mRNA hybridization to examine the spatiotemporal expression of eight receptor-like protein tyrosine phosphatases and find that it is both dynamic and highly varied, including novel, isoform-specific expression patterns. CRYP alpha 1 is expressed in all of the ventral motorneuron pools, whereas CRYP2, RPTP gamma, and RPTP alpha are only expressed in specific subsets of these neurons. CRYP alpha 2, RPTP psi, and RPTP delta are neuronally expressed elsewhere in the cord, but not in ventral motorneurons, whereas RPTP mu is unique in being restricted to capillaries. The developmentally regulated expression of these genes strongly suggests that the encoded phosphatases play numerous roles during neurogenesis and axonogenesis in the vertebrate spinal cord.

Possible role of the receptor protein tyrosine phosphatase HmLAR2 in interbranch repulsion in a leech embryonic cell

Accumulating evidence indicates that receptor protein tyrosine phosphatases (rPTPs) play major roles in growth cone migration. We have previously shown that the growth cones of the multiple parallel processes of an identified leech embryonic cell, the Comb cell (CC), express high levels of a leukocyte antigen-related (LAR)-like rPTP, HmLAR2. Embryonic injection of a polyclonal antibody to the receptor's ectodomain resulted in reduced process outgrowth and in processes crossing over each other, a behavior that is seldom observed in normal or control animals. Here we present results of injecting a soluble Fc-HmLAR2 ectodomain fusion protein into embryos in order to bind the endogenous ligands of HmLAR2. Single injections of the Fc-chimeric protein into the developing embryo resulted, 12 to 24 h postinjection, in clear morphological abnormalities, ranging from abnormally directed CC processes and crossovers to apparent growth cone collapse. At later times, 2 to 5 days post injection, growth cones appeared to have recovered and processes had continued to extend, but effects of the earlier guidance errors remained, with the CCs displaying a relatively high incidence of proximal guidance errors. When injected into the germinal plate of developing embryos, the fusion protein was found to bind selectively to the processes of the CCs themselves, in contrast to control injections of Fc alone or closely related Fc-tagged proteins, which did not decorate the CCs. Double-labeling experiments revealed an early phase of Fc-HmLAR2 labeling (within 20 min after application), during which the growth cones and filopodia of the CC showed significant binding of the receptor ectodomain, and a later phase (1-2 h after injection), when most of the label was redistributed away from the growth cones and into the proximal processes of the CC. In culture, HmLAR2-transfected COS cells were found to selectively bind the Fc-recombinant protein, but not Fc-tagged proteins bearing other closely related receptor ectodomains, demonstrating that the HmLAR2 ectodomain is capable of interacting homophilically. Together, our observations demonstrate that the rPTP HmLAR2 is critically involved in CC process extension through its participation in the regulation of growth cone structure, migration, and navigation. Moreover, since our experiments also indicate that HmLAR2 can bind to itself, we hypothesize that HmLAR2 has a key role in the mechanism of mutual repulsion that maintains the parallel growth of adjacent CC projections.

No obvious abnormality in mice deficient in receptor protein tyrosine phosphatase beta

The development of neurons and glia is governed by a multitude of extracellular signals that control protein tyrosine phosphorylation, a process regulated by the action of protein tyrosine kinases and protein tyrosine phosphatases (PTPs). Receptor PTPbeta (RPTPbeta; also known as PTPzeta) is expressed predominantly in the nervous system and exhibits structural features common to cell adhesion proteins, suggesting that this phosphatase participates in cell-cell communication. It has been proposed that the three isoforms of RPTPbeta play a role in regulation of neuronal migration, neurite outgrowth, and gliogenesis. To investigate the biological functions of this PTP, we have generated mice deficient in RPTPbeta. RPTPbeta-deficient mice are viable, are fertile, and showed no gross anatomical alterations in the nervous system or other organs. In contrast to results of in vitro experiments, our study demonstrates that RPTPbeta is not essential for neurite outgrowth and node formation in mice. The ultrastructure of nerves of the central nervous system in RPTPbeta-deficient mice suggests a fragility of myelin. However, conduction velocity was not altered in RPTPbeta-deficient mice. The normal development of neurons and glia in RPTPbeta-deficient mice demonstrates that RPTPbeta function is not necessary for these processes in vivo or that loss of RPTPbeta can be compensated for by other PTPs expressed in the nervous system.

Proteoglycans in the developing brain: new conceptual insights for old proteins

Proteoglycans are a heterogeneous class of proteins bearing sulfated glycosaminoglycans. Some of the proteoglycans have distinct core protein structures, and others display similarities and thus may be grouped into families such as the syndecans, the glypicans, or the hyalectans (or lecticans). Proteoglycans can be found in almost all tissues being present in the extracellular matrix, on cellular surfaces, or in intracellular granules. In recent years, brain proteoglycans have attracted growing interest due to their highly regulated spatiotemporal expression during nervous system development and maturation. There is increasing evidence that different proteoglycans act as regulators of cell migration, axonal pathfinding, synaptogenesis, and structural plasticity. This review summarizes the most recent data on structures and functions of brain proteoglycans and focuses on new physiological concepts for their potential roles in the developing central nervous system.

Chondroitin sulfate proteoglycan expression pattern in hippocampal development: potential regulation of axon tract formation

A variety of molecular influences in the extracellular matrix (ECM) interact with developing axons to guide the formation of hippocampal axon pathways. One of these influences may be chondroitin sulfate proteoglycans (CSPGs), which are known to inhibit axonal extension during development and following central nervous system injury. In this study, we examined the role of CSPGs and cell adhesion molecules in the regulation of axon tract formation during hippocampal development. We used indirect immunofluorescence to examine the developmental pattern of CSPG expression relative to axon tracts that express the cell adhesion molecule L1. Additionally, we used dissociated and explant cell cultures to examine the effects of CSPGs on hippocampal axon development in vitro. In vivo, we found that the CSPG neurocan is expressed throughout the alveus, neuropil layers, and parts of the dentate gyrus from E16 to P2. The CSPG phosphacan is expressed primarily in the neuropil layers at postnatal stages. After E18, intense labeling of neurocan was observed in regions of the alveus surrounding L1-expressing axon fascicles. In vitro, axons from brain regions that project through the alveus during development would not grow across CSPG substrata, in a concentration-dependent manner. In addition, hippocampal axons from dissociated neuron cultures only traveled across CSPG substrata as fasciculated axon bundles. These findings implicate CSPG in the regulation of axon trajectory and fasciculation during hippocampal axon tract formation.

Dynamic spatiotemporal expression patterns of neurocan and phosphacan indicate diverse roles in the developing and adult mouse olfactory system

The chondroitin sulfate proteoglycans neurocan and phosphacan are believed to modulate neurite outgrowth by binding to cell adhesion molecules, tenascin, and the differentiation factors heparin-binding growth-associated molecule and amphoterin. To assess the role of these chondroitin sulfate proteoglycans in the olfactory system, we describe here their expression patterns during both embryonic and postnatal development in the mouse. Immunoreactivity for neurocan was first detected in primary olfactory neurons at embryonic day 11. 5 (E11.5). Neurocan was expressed by primary olfactory axons as they extended toward the rostral pole of the telencephalon as well as by their arbors in glomeruli after they contacted the olfactory bulb. The role of neurocan was examined by growing olfactory neurons on an extracellular matrix substrate containing neurocan or on extracellular matrix in the presence of soluble neurocan. In both cases, neurocan strongly promoted neurite outgrowth. These results suggest that neurocan supports the growth of primary olfactory axons through the extracellular matrix as they project to the olfactory bulb during development. Phosphacan, unlike neurocan, was present within the mesenchyme surrounding the E11.5 and E12.5 nasal cavity. This expression decreased at E13.5, concomitant with a transient appearance of phosphacan in nerve fascicles. Within the embryonic olfactory bulb, phosphacan was localised to the external and internal plexiform layers. However, during early postnatal development phosphacan was concentrated in the glomerular layer. These results suggest that phosphacan may play a role in delineating the pathway of growing olfactory axons as well as defining the laminar organization of the bulb. Together, the spatiotemporal expression patterns of neurocan and phosphacan indicate that these chondroitin sulfate proteoglycans have diverse in situ roles, which are dependent on context-specific interactions with extracellular and cell adhesion molecules within the developing olfactory nerve pathway.

A receptor-type protein tyrosine phosphatase PTP zeta is expressed in human cutaneous melanomas

We describe the expression of a receptor-type protein tyrosine phosphatase PTP zeta (or RPTP beta) in human cutaneous melanomas as detected by means of immunohistochemistry. The expression of PTP zeta has been described to be restricted to the central nervous system. In developing mice brain high levels of PTP zeta have been detected indicating its developmental importance; PTP zeta is also expressed in glioblastoma and neuroblastoma. By the use of immunohistochemistry we detected PTP zeta in human primary and metastatic melanomas. The melanocytes of healthy skin remained negative. Due to the developmental origin of the melanocytes from neural crest, this represents a further example for transformed cells switching back to express molecules related to their ontogenetic history. These promising initial results have to be verified in larger scaled studies; the inclusion of nevi will be necessary to further elucidate the role of PTP zeta in melanocyte transformation and melanoma development.

Spatiotemporal expression patterns of 6B4 proteoglycan/phosphacan in the developing rat retina

PURPOSE

To investigate expression of 6B4 proteoglycan/phosphacan, the major constituent of chondroitin sulfate proteoglycan and a possible modulator of neural network formation in the developing central nervous system, in developing rat retina.

METHODS

Changes in expression and localization of 6B4 proteoglycan in developing rat retina were investigated by reverse transcription-initiated polymerase chain reaction (RT-PCR), immunohistochemistry, and immunoblot analysis.

RESULTS

Semiquantitative RT-PCR revealed that mRNA expression of 6B4 proteoglycan in retinas peaked at postnatal day 14 (P14) and then decreased at P42. Immunohistochemical analyses using MAb 6B4, a monoclonal antibody against 6B4 proteoglycan, revealed faint immunoreactivity in the inner aspects of the retina at embryonal day 16 (E16). At birth, weak immunoreactivity was present in the nerve fiber layer (NFL) and inner plexiform layer (IPL). At P7 and P14, the NFL, IPL, and outer plexiform layer (OPL) stained intensely, but the ganglion cell layer (GCL) remained unstained. Between P21 and P42, immunoreactivity in the NFL and IPL weakened slightly. Immunoblot analyses showed a MAb 6B4 immunopositive band in the retinal soluble fraction treated with chondroitinase ABC. The amount of the immunopositive band increased rapidly as retinal development proceeded. Surprisingly, a significant amount of the immunopositive band was present in the retina even before digestion with chondroitinase ABC, indicating that at least part of 6B4 proteoglycan in rat retina exists in a non-proteoglycan form.

CONCLUSIONS

The existence of 6B4 proteoglycan/phosphacan was thus demonstrated in rat retina, although some biochemical parameters were different from those of the 6B4 proteoglycan seen in brain.