Neuropilin is a neuronal cell surface protein and has been shown to function as a receptor for a secreted protein, semaphorin III/D, that can induce neuronal growth cone collapse and repulsion of neurites in vitro. The roles of neuropilin in vivo, however, are unknown. Here, we report that neuropilin-deficient mutant mice produced by targeted disruption of the neuropilin gene show severe abnormalities in the trajectory of efferent fibers of the PNS. We also describe that neuropilin-deprived dorsal root ganglion neurons are perfectly protected from growth cone collapse elicited by semaphorin III/D. Our results indicate that neuropilin-semaphorin III/D-mediated chemorepulsive signals play a major role in guidance of PNS efferents.

Diverse protocadherin-alpha genes (Pcdha, also called cadherin-related neuronal receptor or CNR) are expressed in the vertebrate brain. Their genomic organization involves multiple variable exons and a set of constant exons, similar to the immunoglobulin (Ig) and T-cell receptor (TCR) genes. This diversity can be used to distinguish neurons. Using polymorphisms that distinguish the C57BL/6 and MSM mouse strains, we analyzed the allelic expression of the Pcdha gene cluster in individual neurons. Single-cell analysis of Purkinje cells using multiple RT-PCR reactions showed the monoallelic and combinatorial expression of each variable exon in the Pcdha genes. This report is the first description to our knowledge of the allelic expression of a diversified receptor family in the central nervous system. The allelic and combinatorial expression of distinct variable exons of the Pcdha genes is a potential mechanism for specifying neuron identity in the brain.

Neuropilins (NP1 and NP2) are vascular endothelial growth factor (VEGF) receptors that mediate developmental and tumor angiogenesis. Transgenic mice, in which both NP1 and NP2 were targeted (NP1 ؊/؊ NP2 ؊/؊ ) died in utero at E8.5. Their yolk sacs were totally avascular. Mice deficient for NP2 but heterozygous for NP1 (NP1 ؉/؊ NP2 ؊/؊ ) or deficient for NP1 but heterozygous for NP2 (NP1 ؊/؊ NP2 ؉/؊ ) were also embryonic lethal and survived to E10 -E10.5. The E10 yolk sacs and embryos were easier to analyze for vascular phenotype than the fragile poorly formed 8.5 embryos. The vascular phenotypes of these E10 mice were very abnormal. The yolk sacs, although of normal size, lacked the larger collecting vessels and had less dense capillary networks. PECAM staining of yolk sac endothelial cells showed the absence of branching arteries and veins, the absence of a capillary bed, and the presence of large avascular spaces between the blood vessels. The embryos displayed blood vessels heterogeneous in size, large avascular regions in the head and trunk, and blood vessel sprouts that were unconnected. The embryos were about 50% the length of wild-type mice and had multiple hemorrhages. These double NP1͞NP2 knockout mice had a more severe abnormal vascular phenotype than either NP1 or NP2 single knockouts. Their abnormal vascular phenotype resembled those of VEGF and VEGFR-2 knockouts. These results suggest that NRPs are early genes in embryonic vessel development and that both NP1 and NP2 are required. vascular endothelial growth factor ͉ vascular endothelial growth factor receptors ͉ blood vessels ͉ endothelial cells ͉ semaphorins

Neuropilin (previously A5) is a cell surface glycoprotein that was originally identified in Xenopus tadpole nervous tissues. In Xenopus, neuropilin is expressed on both the presynaptic and postsynaptic elements in the visual and general somatic sensory systems, suggesting a role in neuronal cell recognition. In this study, we identified a mouse homologue of neuropilin and examined its expression in developing mouse nervous tissues. cDNA cloning and sequencing revealed that the primary structure of the mouse neuropilin was highly similar to that of Xenopus and that the extracellular segment of the molecule possessed several motifs that were expected to be involved in cell‐cell interaction. Immunohistochemistry and in situ hybridization analyses in mice indicated that the expression of neuropilin was restricted to particular neuron circuits. Neuropilin protein was localized on axons but not on the somata of neurons. The expression of neuropilin persisted through the time when axons were actively growing to form neuronal connections. These observations suggest that neuropilin is involved in growth, fasciculation, and targeting for a particular groups of axons. © 1996 John Wiley & Sons, Inc.

A prevailing view in memory research is that CA3 principally supports spatial processes. However, few studies have investigated the contribution of CA3 to nonspatial memory function. Interestingly, the proximal part of CA3 (close to the dentate gyrus) predominantly projects to distal CA1 (away from the dentate gyrus), which preferentially processes nonspatial information. Moreover, the cytoarchitecture and connectivity patterns in the proximal and distal parts of CA3 strongly differ, suggesting a functional segregation in this area. Here, we tested whether CA3 is recruited during nonspatial recognition memory, and whether nonspatial information is differentially represented along the proximodistal axis of CA3. Furthermore, we investigated whether the pattern of activation within CA3 would mirror that of CA1. We used a high-resolution imaging technique specifically designed to analyze brain activity in distant areas that is based on the detection of the expression of the immediate-early gene Arc, used as a marker of neuronal activation. We showed that proximal CA3 is strongly recruited during a nonspatial delayed nonmatching-to-sample recognition memory task in rats, while distal CA3 is not. In addition, distal CA1 was more activated than proximal CA1 in the same task. These findings suggest a functional segregation of CA3 that mirrors that of CA1, and potentially indicate the existence of a proximal CA3-distal CA1 hippocampal subnetwork that would preferentially process nonspatial information during recognition memory.