Neuropilin-2, a novel member of the neuropilin family, is a high affinity receptor for the semaphorins Sema E and Sema IV but not Sema III

Lymphatic vasculature development

Although the process of blood vasculature formation has been well documented, little is known about lymphatic vasculature development, despite its importance in normal and pathological conditions. The lack of specific lymphatic markers has hampered progress in this field. However, the recent identification of genes that participate in the formation of the lymphatic vasculature denotes the beginning of a new era in which better diagnoses and therapeutic treatment(s) of lymphatic disorders could become a reachable goal.

Neurites from trigeminal ganglion explants grown in vitro are repelled or attracted by tooth-related tissues depending on developmental stage

Although neurite attracting factors are present in the developing dental pulp and trigeminal ganglion (TG) axons can respond to such factors, nerve fibres do not enter the tooth pulp until a late developmental stage compared with surrounding tissues supplied by the TG. This suggests that the dental pulp secretes neurite growth inhibitory molecules. Semaphorins represent one group of substances, which can inhibit/repel growing neurites. The aims of the present study were to investigate if dental tissue explants inhibit/repel neurite growth from TGs at some developmental stages in vitro, and if so, to seek evidence for or against a participation of semaphorins in that interaction. By co-culturing mandibular or dental epithelial and mesenchymal tissue explants and TGs in collagen gels, we found that embryonic day 11 (E11) mandibular and E13 dental mesenchymal explants repel neurites from corresponding TGs. Repulsion was replaced by attraction if tissues from late embryonic or early postnatal mice (E17-postnatal day 5) were used. Using semi-quantitative reverse transcription/polymerase chain reaction we showed that a number of semaphorins were expressed by tooth-related mesenchyme collected from embryonic and postnatal mice. The expression of some semaphorins (3A, 3C, 3F, 4F, 5B, 6A, 6B and 6C) was high early in development and then decreased in a temporal pattern that correlated with neurite inhibitory/repulsive effects of dental mesenchyme observed in co-cultures. The expression of other semaphorins increased with development (3B, 4A and 7A), whilst others varied irregularly or remained at a fairly constant level (3E, 4B, 4C, 4D, 4G and 5A). Immunohistochemistry was used to determine if tooth-related nerve fibres possess neuropilins. This revealed that axons surrounding embryonic tooth buds express neuropilin-1, but not neuropilin-2. In postnatal teeth, nerve fibres located within the tooth pulp were immunonegative for neuropilin-1 and neuropilin-2. We conclude that developing mandibular/dental mesenchyme can inhibit/repel neurite growth in vitro. Our results support the hypothesis that semaphorins may be involved in this interaction.

Cranial expression of class 3 secreted semaphorins and their neuropilin receptors

The semaphorin family of chemorepellents and their receptors the neuropilins are implicated in a variety of cellular processes, including axon guidance and cell migration. Semaphorins may bind more than one neuropilin or a heterodimer of both, thus a detailed knowledge of their expression patterns may reveal possible cases of redundancy or mutual antagonism. To assess their involvement in cranial development, we cloned fragments of the chick orthologues of Sema3B and Sema3F. We then carried out mRNA in situ hybridisation of all six class 3 semaphorins and both neuropilins in the embryonic chick head. We present evidence for spatiotemporal regulation of these molecules in the brainstem and developing head, including the eye, ear, and branchial arches. These expression patterns provide a basis for functional analysis of semaphorins and neuropilins in the development of axon projections and the morphogenesis of cranial structures.

Role of β-catenin in the developing cortical and hippocampal neuroepithelium

beta-Catenin plays a pivotal role in Wnt signaling during embryogenesis and is a component of adherens junctions. Since targeted disruption of the beta-catenin gene is lethal at gastrulation we have used a D6-Cre mouse line for conditional inactivation of beta-catenin in the mouse cerebral cortex and hippocampus after embryonic day (E) 10.5. In D6-Cre floxed beta-catenin mice, hippocampal CA1-CA2 fields are disrupted in similar manner as in Wnt-3a and LEF-1 mutants. The cortex of D6-Cre floxed beta-catenin mutants is strongly affected which contrasts with the normal cortex observed in Wnt-3a and LEF-1 mutants. Severe abnormalities in the organization of the neuroepithelium are observed that include disrupted interkinetic nuclear migration, loss of adherens junctions, impaired radial migration of neurons toward superficial layers and decreased cell proliferation after E15.5. At newborn stage, a premature disassembly of the radial glial scaffold and increased numbers of astrocytes are found in the cortex.

Semaphorin 3F antagonizes neurotrophin-induced phosphatidylinositol 3-kinase and mitogen-activated protein kinase kinase signaling: a mechanism for growth cone collapse

Peripheral nerve growth is regulated by the coordinated action of numerous external stimuli, including positively acting neurotrophin-derived growth cues and restrictive semaphorin cues. Here, we show that Semaphorin 3F (Sema 3F) can antagonize nerve growth factor (NGF)-stimulated TrkA (tyrosine receptor kinase A) signaling in sympathetic neurons, thereby apparently contributing to growth cone collapse. Sema 3F suppressed NGF-induced activation of the phosphatidylinositol 3 (PI3)-kinase-Akt and MEK (mitogen-activated protein kinase kinase)-ERK (extracellular signal-regulated kinase) pathways, both of which we show to be required to maintain growth cone structure. Sema 3F-induced growth cone collapse was partially reversed by sustained activation of the PI3-kinase and MEK pathways, which was achieved by overexpression of the Gab-1 (growth-associated binder 1) docking protein. These data indicate that a novel mechanism used by Sema 3F to collapse growth cones in sympathetic neurons is to dampen neurotrophin signaling, providing an intracellular mechanism for cross talk between positive and negative axon growth cues.

Semaphorin 3F is critical for development of limbic system circuitry and is required in neurons for selective CNS axon guidance events

Little is known about the role of class 3 semaphorins in the development of CNS circuitry. Several class 3 semaphorins, including semaphorin 3F (Sema3F) bind to the receptor neuropilin-2 to confer chemorepulsive responses in vitro. To understand the role of Sema3F in the establishment of neural circuitry in vivo, we have generated sema3F null and sema3F conditional mutant mice. Inspection of the peripheral nervous system in sema3F null mice reveals that Sema3F is essential for the proper organization of specific cranial nerve projections. Analysis of the CNS in sema3F null mice reveals a crucial role for Sema3F in the rostral forebrain, midbrain, and hippocampus in establishing specific Npn-2 (neuropilin-2)-expressing limbic tracts. Furthermore, we identify Sema3F and Npn-2 as the first guidance cue-receptor pair shown to be essential for controlling the development of amygdaloid circuitry. In addition, we provide genetic evidence in vertebrates for a neuronal requirement of a soluble axon guidance cue in CNS axon guidance. Our data reveal a requirement for neuronal Sema3F in the normal development of the anterior commissure in the ventral forebrain and infrapyramidal tract in the hippocampus. Thus, our results show that Sema3F is the principal ligand for Npn-2-mediated axon guidance events in vivo and is a critical determinant of limbic and peripheral nervous system circuitry.

Neuropilin-1 conveys semaphorin and VEGF signaling during neural and cardiovascular development

Neuropilin-1 (Npn-1) is a receptor that binds multiple ligands from structurally distinct families, including secreted semaphorins (Sema) and vascular endothelial growth factors (VEGF). We generated npn-1 knockin mice, which express an altered ligand binding site variant of Npn-1, and npn-1 conditional null mice to establish the cell-type- and ligand specificity of Npn-1 function in the developing cardiovascular and nervous systems. Our results show that VEGF-Npn-1 signaling in endothelial cells is required for angiogenesis. In striking contrast, Sema-Npn-1 signaling is not essential for general vascular development but is required for axonal pathfinding by several populations of neurons in the CNS and PNS. Remarkably, both Sema-Npn-1 signaling and VEGF-Npn-1 signaling are critical for heart development. Therefore, Npn-1 is a multifunctional receptor that mediates the activities of structurally distinct ligands during development of the heart, vasculature, and nervous system.

Expression of VEGF, semaphorin SEMA3F, and their common receptors neuropilins NP1 and NP2 in preinvasive bronchial lesions, lung tumours, and cell lines

Two receptors, neuropilin 1 (NP1) and neuropilin 2 (NP2), bind class 3 semaphorins, axon guidance molecules including SEMA3F, the gene for which was isolated from a 3p21.3 deletion in lung cancer. In addition, they bind VEGF (vascular endothelial growth factor), enhancing the effects of VEGF binding to KDR/Flk-1. Elevated VEGF levels are associated with the loss and cytoplasmic delocalization of SEMA3F in lung cancer, suggesting competition for their NP1 and NP2 receptors. To determine the timing of these events, we compared by immunohistochemistry VEGF, SEMA3F, NP1 and NP2 expression in 50 preneoplastic lesions and 112 lung tumours. In preneoplastic lesions, VEGF increased from low-grade to high-grade dysplasia (p=0.001) whereas SEMA3F levels remained low. NP1 and NP2 levels increased from dysplasia to microinvasive carcinoma (p=0.0001) and correlated with VEGF expression (p=0.04 and 0.0002, respectively). Non-small cell lung carcinoma overexpressed VEGF and NP1 and NP2 significantly more often than neuroendocrine tumours including small cell lung carcinoma. SEMA3F loss or delocalization correlated with advanced tumour stage. Migrating cells overexpressed VEGF, SEMA3F, NP1 and NP2 with cytoplasmic delocalization of NP1 as demonstrated in an in vitro wound assay. These results demonstrate early alteration of the VEGF/SEMA3F/NP pathway in lung cancer progression.

Novel expression of vascular endothelial growth factor receptor (VEGFR)-3 and VEGF-C on corneal dendritic cells

Vascular endothelial growth factor-3 (VEGFR-3) plays a critical role in embryonic cardiovascular development and is thought to be expressed exclusively on the lymphatic endothelium, high endothelial venules, and rarely on adult vascular endothelium. Recent evidence also suggests expression of VEGFR-3 on some tumor-associated macrophages. We have studied the expression of VEGFR-3, its ligand VEGF-C and the co-receptor neuropilin-2, in normal and inflamed corneas and characterized the phenotype and distribution of VEGFR-3(+) cells. Our data demonstrate, for the first time, the expression of VEGFR-3 on corneal dendritic cells (DC) and its up-regulation in inflammation. VEGFR-3(+) DC are CD11c(+)CD45(+)CD11b(+), and are mostly major histocompatibility (MHC) class II(-)CD80(-)CD86(-), indicating immature DC of a monocytic lineage. During inflammation, there is rapid increase in the number of VEGFR-3(+) DC in the cornea associated with heightened membranous expression as compared to a mostly intracellular expression in uninflamed tissue. VEGFR-3(+) DC in normal corneas are VEGF-C(-)neuropilin-2(-), but express VEGF-C in inflammation. Interestingly, similar cells are absent both in the normal and inflamed skin. These data demonstrate, for the first time, the expression of VEGFR-3 and VEGF-C on tissue DC, which implicate a novel potential relationship between lymphangiogenesis and leukocyte trafficking in the eye.

A role for semaphorins and neuropilins in oligodendrocyte guidance

Oligodendrocytes develop in defined CNS regions as progenitor cells, which migrate to their final destinations, encountering soluble and membrane-bound signals that influence their differentiation and potential to myelinate axonal projections. To identify the regulatory genes that may be involved in this process, microarray analysis of developing oligodendroglia was performed. Several neural guidance genes, including members of the neuropilin (NP) and semaphorin families were detected. These findings were verified and expanded upon using RT-PCR with RNA from fluorescent activated cell sorted A2B5+ oligodendrocyte progenitors and O4+ pro-oligodendrocytes isolated from in vitro and in vivo sources. RT-PCR, western and immunocytochemical analyses revealed that oligodendrocytes expressed NP1, several alternatively spliced isoforms of NP2, and a broad spectrum of both soluble (Class 3), membrane-spanning (Class 4-6), and membrane-tethered (Class 7) semaphorin ligands. Class 3 semaphorins, in a modified stripe assay, caused the collapse of oligodendrocyte progenitor growth cones, redirection of processes, and altered progenitor migration. Our data support a role for neuropilins and semaphorins in orchestrating the migration patterns of developing oligodendrocytes in the CNS.

Human malignant glioma cells express semaphorins and their receptors, neuropilins and plexins

Semaphorins comprise a family of molecules implicated in the guiding of growing axons and neuronal progenitor cells. Further, semaphorins have been suggested to play a role in cancer metastasis. Neuropilins 1 and 2 are cell surface receptors for soluble class 3 semaphorins. Plexins are direct receptors for membrane-bound semaphorins and, by binding to neuropilins, coreceptors necessary for class 3 semaphorin signaling. We here report that human malignant glioma cell lines express neuropilins 1 and 2 mRNA and protein, as well as either plexin A1, A2, or B1. Further, all glioma cell lines express SEMA3A and SEMA3C and exhibit SEMA3A binding sites. Exogenous SEMA3A expressed in 293 or U87MG cells has no collapsing or chemorepulsive activities on glioma cells as determined by F-actin staining and collagen coculture assays. In summary, human glioma cells express class 3 semaphorins and receptors for soluble and membrane-bound semaphorins, suggesting a possible role of the semaphorin/neuropilin system in the interactions of human malignant glioma with the host's central nervous and immune systems.

Signaling pathways in vascular development

The vasculature is one of the most important and complex organs in the mammalian body. The first functional organ to form during embryonic development, the intricately branched network of endothelial and supporting periendothelial cells is essential for the transportation of oxygen and nutrients to and the removal of waste products from the tissues. Serious disruptions in the formation of the vascular network are lethal early in post-implantation development, while the maintenance of vessel integrity and the control of vessel physiology and hemodynamics have important consequences throughout embryonic and adult life. A full understanding of the signaling pathways of vascular development is important not just for understanding normal development but because of the importance of reactivation of angiogenic pathways in disease states. Clinically there is a need to develop therapies to promote new blood vessel formation in situations of severe tissue ischemia, such as coronary heart disease. In addition, there is considerable interest in developing angiogenic inhibitors to block the new vessel growth that solid tumors promote in host tissue to enhance their own growth. Already studies on the signaling pathways of normal vascular development have provided new targets for therapeutic intervention in both situations. Further understanding of the complexities of the pathways should help refine such strategies.

High diversity of non-human leukocyte antigens in transplant-associated coronary artery disease

BACKGROUND

Antibodies to endothelial derived non-human leukocyte antigens (HLA) have been associated with transplant (Tx)-associated coronary artery disease (CAD) after cardiac transplantation; however, few have been identified. The aim of this study was to screen a human coronary artery endothelial cell cDNA library with patient sera to establish the diversity and nature of the target antigens.

METHODS

A human coronary artery endothelial cell cDNA library was screened with sera from seven long-term cardiac transplant patients with angiographically diagnosed TxCAD and sera from five healthy volunteers.

RESULTS

Of the seven patients' sera, five showed reactivity, as did sera from two of the five normal subjects. Eighteen positive cDNA clones were isolated by TxCAD sera; DNA sequence analysis and DNA database searching identified all but one clone; 16 were nuclear or cytoplasmic proteins and 1 of them was the cell surface protein neuropilin 2. Five clones were targeted by normal sera. A different spectrum of reactive clones was identified by the sera of each patient where reactive clones were evident.

CONCLUSIONS

A high diversity of non-HLA antigens, probably autoantigens, are involved in the pathogenesis of TxCAD.

Temporal specific patterns of semaphorin gene expression in rat brain after kainic acid-induced status epilepticus

Mossy fiber sprouting and other forms of synaptic reorganization may form the basis for a recurrent excitatory network in epileptic foci. Four major classes of axon guidance molecules--the ephrins, netrins, slits, and semaphorins--provide targeting information to outgrowing axons along predetermined pathways during development. These molecules may also play a role in synaptic reorganization in the adult brain and thereby promote epileptogenesis. We studied semaphorin gene expression, as assessed by in situ hybridization, using riboprobes generated from rat cDNA in an adult model of synaptic reorganization, kainic acid (KA)-induced status epilepticus (SE). Within the first week after KA-induced SE, semaphorin 3C, a class III semaphorin, mRNA content is decreased in the CA1 area of the hippocampus and is increased in the upper layers of cerebral cortex. Another class III semaphorin, semaphorin 3F, is also decreased in CA1 and CA3 of hippocampus within the first week after KA-SE. These changes in gene expression are principally confined to neurons. By contrast, there was little change in the semaphorin 4C mRNA content of CA1 neurons at this time. No changes in expression of semaphorin 3A and 4C genes were detected 28 days after KA-induced SE. Regulation of semaphorin gene expression after KA-induced SE suggests that neurons may regulate the expression of axonal guidance molecules and thereby contribute to synaptic reorganization after injury of the mature brain. The anatomic locale of the altered semaphorin gene expression may serve as a marker for specific networks undergoing synaptic reorganization in the epileptic brain.

From the discovery of neuropilin to the determination of its adhesion sites

Neuropilin (NRP) and plexin (Plex) that are now known to be semaphorin receptors were initially identified as antigens for monoclonal antibodies (MAbs) that bound to particular neuropiles and plexiform layers of the Xenopus tadpole optic tectum, several years before the discovery of semaphorin. The extracellular segment of the NRP protein is a mosaic of 3 functionally different protein motifs that are thought to be involved in molecular and/or cellular interactions, suggesting that NRP serves in a various cell-cell interaction by binding a variety of molecules. The first identified function of NRP was the cell adhesion activity; Cell reaggregation study using NRP-expressing cell lines revealed that NRP can mediate cell adhesion via heterophilic molecular interaction. Later, NRP was shown to bind semaphorins and vascular endothelial growth factor (VEGF). It was also shown that NRP makes receptor complexes with Plex to propagate semaphorin signals.

Molecular analysis of axon repulsion by the notochord

During development of the amniote peripheral nervous system, the initial trajectory of primary sensory axons is determined largely by the action of axon repellents. We have shown previously that tissues flanking dorsal root ganglia, the notochord lying medially and the dermamyotomes lying laterally, are sources of secreted molecules that prevent axons from entering inappropriate territories. Although there is evidence suggesting that SEMA3A contributes to the repellent activity of the dermamyotome, the nature of the activity secreted by the notochord remains undetermined. We have employed an expression cloning strategy to search for axon repellents secreted by the notochord, and have identified SEMA3A as a candidate repellent. Moreover, using a spectrum of different axon populations to assay the notochord activity, together with neuropilin/Fc receptor reagents to block semaphorin activity in collagen gel assays, we show that SEMA3A probably contributes to notochord-mediated repulsion. Sympathetic axons that normally avoid the midline in vivo are also repelled, in part, by a semaphorin-based notochord activity. Although our results implicate semaphorin signalling in mediating repulsion by the notochord, repulsion of early dorsal root ganglion axons is only partially blocked when using neuropilin/Fc reagents. Moreover, retinal axons, which are insensitive to SEMA3A, are also repelled by the notochord. We conclude that multiple factors act in concert to guide axons in this system, and that further notochord repellents remain to be identified.

Characterization of the neuropilin-1 promoter; gene expression is mediated by the transcription factor Sp1

Neuropilin-1 (NRP1) is a receptor for the vascular endothelial growth factor (VEGF) family of angiogenesis factors and for the semaphorin family of secreted neuronal guidance polypeptides. Very little is known, however, about how NRP1 gene expression is regulated. In this study, it was demonstrated that the tumor promoter, TPA (12-O-tetradecanoylphorbol-13-acetate) significantly up-regulated NRP1 mRNA levels by increasing its gene transcription rate in a manner dependent on de novo protein synthesis. To determine which elements regulate functional NRP1 expression, the promoter regions of human and mouse NRP1 genes were cloned and characterized. Promoter-reporter gene transfection experiments using deletion and point mutations demonstrated that two Sp1 elements are major contributors to both the constitutive and TPA-induced activity of the NRP1 promoter. Gel shift analysis showed a specific binding of the Sp1 transcription factor to those elements. Further mutational analysis revealed that an AP-1, and a CCAAT box also contributed to NRP1 constitutive and TPA-induced promoter activity. It was concluded that NRP1 expression is regulated by the cooperation of several regulatory elements including AP-1, Sp1, and a CCAAT box.

Neuropilin-1 on hematopoietic cells as a source of vascular development

Neuropilin-1 (NP-1) is a receptor for vascular endothelial growth factor-165 (VEGF165) and acts as a coreceptor that enhances the function of VEGF165 through VEGF receptor-2 (VEGFR-2). Studies using transgenic and knock-out mice of NP-1 indicated that this molecule is important for vascular development as well as neuronal development. We recently reported that clustered soluble NP-1 phosphorylates VEGFR-2 on endothelial cells with a low dose of VEGF165 and rescues the defective vascularity of the NP-1-/- embryo in vitro and in vivo. Here we show that NP-1 is expressed by CD45+ hematopoietic cells in the fetal liver, can bind VEGF165, and phosphorylates VEGFR-2 on endothelial cells. CD45+NP-1+ cells rescued the defective vasculogenesis and angiogenesis in the NP-1-/- P-Sp (para-aortic splanchnopleural mesodermal region) culture, although CD45+NP-1- cells did not. Moreover, CD45+NP-1+ cells together with VEGF165 induced angiogenesis in an in vivo Matrigel assay and cornea neovascularization assay. The extracellular domain of NP-1 consists of "a," "b," and "c" domains, and it is known that the "a" and "c" domains are necessary for dimerization of NP-1. We found that both the "a" and "c" domains are essential for such rescue of defective vascularities in the NP-1 mutant. These results suggest that NP-1 enhances vasculogenesis and angiogenesis exogenously and that dimerization of NP-1 is important for enhancing vascular development. In NP-1-/- embryos, vascular sprouting is impaired at the central nervous system (CNS) and pericardium where VEGF is not abundant, indicating that NP-1-expressing cells are required for normal vascular development.

Identification and characterization of a novel mouse plexin, plexin-A4

Plexins belonging to the plexin-A subfamily form complexes with neuropilins and propagate signals of class 3 semaphorins into neurons, even though they do not directly bind the semaphorins. In this study, we identified a new member of the plexin-A subfamily in the mice, plexin-A4, and showed that it was expressed in the developing nervous system with a pattern different to that of other members of the plexin-A subfamily (plexin-A1, plexin-A2 and plexin-A3). COS-7 cells coexpressing plexin-A4 with neuropilin-1 were induced to contract by Sema3A, a member of the class 3 semaphorin. Ectopic expression of plexin-A4 in mitral cells that are originally insensitive to Sema3A resulted in the collapse of growth cones in the presence of Sema3A. These results suggest that plexin-A4 plays a role in the propagation of Sema3A activities.

Angiogenesis of the heart

Despite continued advances in the prevention and treatment of coronary artery disease, there are still a large number of patients who are not candidates for the conventional revascularization techniques of balloon angioplasty and stenting, or coronary artery bypass grafting (CABG). Therapeutic angiogenesis, in the form of the administration of growth factor protein or gene therapy, has emerged as a promising new method of treatment for patients with coronary artery disease. The goal of this strategy is to promote the development of supplemental blood conduits that will act as endogenous bypass vessels. New vessel formation occurs through the processes of angiogenesis, vasculogenesis, and arteriogenesis, under the control of growth factors such as those that belong to the vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF) and angiopoeitin (Ang) families of molecules. Preclinical studies have suggested that such an approach is both feasible and effective; however many questions remain to be answered. This review will address the elements of pharmacologic revascularization, focusing on gene and protein-based therapy. The important growth factors, the vector (for gene therapy), routes of delivery, the desired therapeutic effect, and quantifiable clinical end points for trials of angiogenesis will all be addressed.

Semaphorin junction: making tracks toward neural connectivity

Semaphorins constitute one of the largest families of repulsive and attractive growth cone guidance proteins. They affect the growth cone's actin cytoskeleton through interactions with receptor complexes composed of ligand-binding, signal-transducing, and modulatory subunits. Our understanding of the intracellular signal transduction machinery linking semaphorins to actin dynamics is limited; however, recent advances provide a more comprehensive view of the molecular basis of neuronal semaphorin signaling.

Hippocampal heterotopia with molecular and electrophysiological properties of neocortical neurons

Cortical malformations resulting from aberrant brain development can be associated with mental retardation, dyslexia, and intractable forms of epilepsy. Despite emerging interest in the pathology and etiology of cortical malformations, little is known about the phenotype of cells within these lesions. In utero exposure to the DNA methylating agent methylazoxymethanol acetate (MAM) during a critical stage in neurodevelopment results in animals with distinct clusters of displaced neurons in hippocampus, i.e. nodular heterotopia. Here we examined the molecular and electrophysiological properties of cells within hippocampal heterotopia using rats exposed to MAM during gestation. Molecular analysis revealed that heterotopic cells do not express mRNA markers normally found in hippocampal pyramidal cells or dentate granule cells (SCIP, Math-2, Prox-1, neuropilin-2). In contrast, Id-2 mRNA, normally abundant in Layer II-III supragranular neocortical neurons but not in CA1 pyramidal neurons, was prominently expressed in hippocampal heterotopia. Current-clamp analysis of the firing properties of heterotopic neurons revealed a striking similarity with supragranular cortical neurons. In particular, both cells were characterized by small hyperpolarizing 'sag' potentials, high input resistance values, slow spike-train afterhyperpolarizations, and the absence of a depolarizing afterpotential. Normotopic CA1 pyramidal neurons (e.g. pyramidal cells with normal lamination adjacent to a heterotopia) in the MAM brain exhibited molecular and electrophysiological properties that were nearly identical to those of age-matched CA1 pyramidal neurons from control rats. We conclude that neuronal heterotopiae in the hippocampus of MAM-exposed rats are comprised of neurons with a Layer II-III supragranular cortex phenotype. The MAM model, therefore, may serve as a useful tool in examination of the factors influencing aberrant brain development and epilepsy.

VEGF-RII influences the prognosis of pancreatic cancer

OBJECTIVE

To evaluate whether the vascular endothelial growth factor (VEGF) pathway can be used as a target for effective treatment of pancreatic cancer.

SUMMARY BACKGROUND DATA

VEGF and its receptors (VEGF-RI and -RII) are the predominant regulators of tumor neoangiogenesis, a key element for tumor growth and progression. However, VEGF receptor expression has been thought to be limited to endothelial cells, limiting the possibility of targeting it for therapy of pancreatic cancer.

METHODS

Protein localization and mRNA were studied in pancreatic cancer specimens, normal pancreas, human pancreatic cancer cell lines, and an endothelial cell line. Cell proliferation was determined by [ H] thymidine uptake. Both VEGF receptors were genetically eliminated by antisense technology. The same approach was used in a murine model of pancreatic cancer in a therapeutic approach.

RESULTS

VEGF-RI mRNA and VEGF-RII mRNA were expressed in 17 and 15 of 24 pancreatic cancer samples, respectively. VEGF receptors were found not only in blood vessels but also in pancreatic cancer cells. VEGF-RII expression correlated with poor tumor differentiation and was associated with poorer survival, while VEGF-RI expression did not correlate. VEGF treatment led to extensive growth stimulation in six of seven pancreatic cancer cell lines, which was completely inhibited by antisense treatment against VEGF-RII. Liposome-mediated gene transfer in nude mice with pancreatic tumors markedly reduced local tumor growth and decreased metastatic tumor spread.

CONCLUSIONS

The VEGF/VEGF-RII pathway regulates angiogenesis and local tumor growth and spread in pancreatic cancer. Genetic targeting of VEGF-RII blocks local growth and metastatic spread of pancreatic cancer cells in vivo and therefore offers a potential new therapeutic option for patients with this disease.

Evidence that Sema3A and Sema3F regulate the migration of GABAergic neurons in the developing neocortex

The ganglionic eminence (GE) supplies neurons containing gamma-aminobutyric acid (GABA) to the pallium of the telencephalon. We investigated the molecular guidance mechanisms of GE cell migration in the neocortex and found neuropilin-1 (Npn-1) or neuropilin-2 (Npn-2) on the GE cells. Ectopic Sema3A or -3F expression by COS1 cell clusters placed on embryo neocortical slices reduced the cell migration but did not block it completely. However, the cell migration was almost completely blocked by COS1 cell clusters expressing both Sema3A and -3F. The direction of cell migration could be reversed by placing Sema3A- and -3F-coexpressing COS1 cell clusters at the distal cut end of the neocortical slices. Further slice experiments revealed that migration of half of the GE cells in the neocortex was regulated by Sema3A and that migration of the other half of the GE cells in the neocortex was regulated by Sema3F. When the cells responding to Sema3A were diverted by ectopic Sema3A expression in vivo, Dlx2-positive cells were found predominantly in the lower intermediate zone (IZ). When the cells responding to Sema3F were diverted by ectopic Sema3F expression in vivo, Dlx2-positive cells were found predominantly in the upper IZ. It was speculated that the semaphorin-neuropilin interactions distribute the GABAergic GE cells evenly in the neocortex as well as guide the GE cells from the GE to the neocortex. The Sema3A expression site under the subplate extended dorsally as the embryo developed. The Sema3A expression seemed to block the Npn-1-positive GE cells in the neocortex from entering the cortical plate (CP) and guide them to the dorsal cortex and the hippocampus. Sema3F expression in the CP continued through the embryonic stages. The expression seemed to block Npn-2-positive GE cells in the neocortex from entering the CP and make them migrate into the lower IZ. Finally, the semaphorin-neuropilin interactions sorted GABAergic inteneurons into the CP and white matter neurons into the IZ.

Semaphorin SEMA3F and VEGF have opposing effects on cell attachment and spreading

SEMA3F, isolated from a 3p21.3 deletion, has antitumor activity in transfected cells, and protein expression correlates with tumor stage and histology. In primary tumors, SEMA3F and VEGF surface staining is inversely correlated. Coupled with SEMA3F at the leading edge of motile cells, we previously suggested that both proteins competitively regulate cell motility and adhesion. We have investigated this using the breast cancer cell line, MCF7. SEMA3F inhibited cell attachment and spreading as evidenced by loss of lamellipodia extensions, membrane ruffling, and cell-cell contacts, with cells eventually rounding-up and detaching. In contrast, VEGF had opposite effects. Although SEMA3F binds NRP2 with 10-fold greater affinity than NRP1, the effects in MCF7 were mediated by NRP1. This was determined by receptor expression and blocking of anti-NRP1 antibodies. Similar effects, but through NRP2, were observed in the C100 breast cancer cell line. Although we were unable to demonstrate changes in total GTP-bound Rac1 or RhoA, we did observe changes in the localization of Rac1-GFP using time lapse microscopy. Following SEMA3F, Rac1 moved to the base of lamellipodia and - with their collapse - to the membrane. These results support the concept that SEMA3F and VEGF have antagonistic actions affecting motility in primary tumor cell.

Crystal structure of the human neuropilin-1 b1 domain

Neuropilin-1 (Npn-1) is a type I cell surface receptor involved in a broad range of developmental processes, including axon guidance, angiogenesis, and heterophilic cell adhesion. We have determined the crystal structure of the human Npn-1 b1 domain to 1.9 A. The overall structure resembles coagulation factor V and VIII (F5/8) C1 and C2 domains, exhibiting a distorted jellyroll fold. Details of the structure provide insight to b1 domain regions responsible for ligand binding and facilitate rationalization of existing biochemical binding data. A polar cleft formed by adjacent loops at one end of the molecule in conjunction with flanking electronegative surfaces may represent the binding site for the positively charged tails of semaphorins and VEGF(165). The nature of the cell adhesion binding site of the b1 domain can be visualized in context of the structure.

Anti-semaphorin 3A antibodies rescue retinal ganglion cells from cell death following optic nerve axotomy

Damage to the optic nerve in mammals induces retrograde degeneration and apoptosis of the retinal ganglion cell (RGC) bodies. The mechanisms that mediate the response of the neuronal cells to the axonal injury are still unknown. We have previously shown that semaphorins, axon guidance molecules with repulsive cues, are capable of mediating apoptosis in cultured neuronal cells (Shirvan, A., Ziv, I., Fleminger, G., Shina, R., He, Z., Brudo, I., Melamed, E., and Brazilai, A. (1999) J. Neurochem. 73, 961-971). In this study, we examined the involvement of semaphorins in an in vivo experimental animal model of complete axotomy of the rat optic nerve. We demonstrate that a marked induction of type III semaphorin proteins takes place in ipsilateral retinas at early stages following axotomy, well before any morphological signs of RGC apoptosis can be detected. Time course analysis revealed that a peak of expression occurred after 2-3 days and then declined. A small conserved peptide derived from semaphorin 3A that was previously shown to induce neuronal death in culture was capable of inducing RGC loss upon its intravitreous injection into the rat eye. Moreover, we demonstrate a marked inhibition of RGC loss when axotomized eyes were co-treated by intravitreous injection of function-blocking antibodies against the semaphorin 3A-derived peptide. Marked neuronal protection from degeneration was also observed when the antibodies were applied 24 h post-injury. We therefore suggest that semaphorins are key proteins that modulate the cell fate of axotomized RGC. Neutralization of the semaphorin repulsive function may serve as a promising new approach for treatment of traumatic injury in the adult mammalian central nervous system or of ophthalmologic diseases such as glaucoma and ischemic optic neuropathy that induce apoptotic RGC death.

Wiring of the brain by a range of guidance cues

During development of the central nervous system, growth cones navigate along specific pathways, recognize their targets and then form synaptic connections by elaborating terminal arbors. To date, a number of developmental and in vitro studies have characterized the nature of the guidance cues that underlie various types of axonal behavior, from initial outgrowth to synapse formation, including pathway selection, polarized growth, orientated growth, termination and branching. New approaches in molecular biology have identified several types of guidance cues, most of which are likely to act as local cues. Moreover, recent studies have indicated that axonal responsiveness to guidance cues changes dynamically, which appears to be elicited by environmental factors encountered by the navigating growth cones. This article addresses what molecular cues are responsible for guidance mechanisms including axonal responsiveness, focusing on axonal behavior in the developmental stages.

VEGF-RII influences the prognosis of pancreatic cancer

OBJECTIVE

To evaluate whether the vascular endothelial growth factor (VEGF) pathway can be used as a target for effective treatment of pancreatic cancer.

SUMMARY BACKGROUND DATA

VEGF and its receptors (VEGF-RI and -RII) are the predominant regulators of tumor neoangiogenesis, a key element for tumor growth and progression. However, VEGF receptor expression has been thought to be limited to endothelial cells, limiting the possibility of targeting it for therapy of pancreatic cancer.

METHODS

Protein localization and mRNA were studied in pancreatic cancer specimens, normal pancreas, human pancreatic cancer cell lines, and an endothelial cell line. Cell proliferation was determined by [ H] thymidine uptake. Both VEGF receptors were genetically eliminated by antisense technology. The same approach was used in a murine model of pancreatic cancer in a therapeutic approach.

RESULTS

VEGF-RI mRNA and VEGF-RII mRNA were expressed in 17 and 15 of 24 pancreatic cancer samples, respectively. VEGF receptors were found not only in blood vessels but also in pancreatic cancer cells. VEGF-RII expression correlated with poor tumor differentiation and was associated with poorer survival, while VEGF-RI expression did not correlate. VEGF treatment led to extensive growth stimulation in six of seven pancreatic cancer cell lines, which was completely inhibited by antisense treatment against VEGF-RII. Liposome-mediated gene transfer in nude mice with pancreatic tumors markedly reduced local tumor growth and decreased metastatic tumor spread.

CONCLUSIONS

The VEGF/VEGF-RII pathway regulates angiogenesis and local tumor growth and spread in pancreatic cancer. Genetic targeting of VEGF-RII blocks local growth and metastatic spread of pancreatic cancer cells in vivo and therefore offers a potential new therapeutic option for patients with this disease.

Neuropilin-2 is overexpressed in the rat brain after limbic seizures

Structural rearrangement and synaptic reorganization are known to occur in the brain after seizures. If neuronal rearrangement after seizures always results in abnormal hyperexcitability, it would provide an accurate pathway to the appropriate target and as a result, it may be the mechanism of epileptogenesis. This study examined the mechanism of axon guidance in the mature rat brain after seizures by evaluating the expression of the axonal guidance molecule, neuropilin-2. We assessed the expression of neuropilin-2 by northern blotting and immunohistochemistry in rat with seizures created by kindling stimulation and kainate injection.The neuropilin-2 mRNA level was increased in the whole brain of the rats at 24 h after either type of seizure. Neuropilin-2 mRNA was not increased at 2 weeks after the last stimulation. Immunohistochemistry demonstrated that neuropilin-2 protein was increased in the dentate gyrus and the entorhinal cortex in the both seizure models. These findings suggested that there was overexpression of neuropilin-2 in the brains of mature rats with different types of seizure. Accordingly, neuropilin-2 might regulate remodeling after seizures as it does during the development of the hippocampal formation. Our findings suggest that axons may not project and outgrow 'aberrantly' after seizures, but may be regulated by the chemorepellent effect through neuropilin-2.

Neuropilin 1 and neuropilin 2 co-expression is significantly correlated with increased vascularity and poor prognosis in nonsmall cell lung carcinoma

BACKGROUND

Cell-retained isoforms of vascular endothelial growth factor A (VEGF-A) have been reported to play an essential role in tumor progression through stromal neovascularization in malignant solid tumors. While more than 95% of nonsmall cell lung carcinoma (NSCLC) expresses cell-retained VEGF-A isoform, the clinicopathologic implications of neuropilin (NRP), considered the specific receptor for limited types of VEGF-A isoform, are not well understood.

METHODS

The authors examined NRP1 and NRP2 mRNA expression in 68 NSCLCs and 15 extraneoplastic tissues by a densitometry-assisted, semi-quantitative reverse transcription-polymerase chain reaction. The authors determined the distinct expression of NRPs using the expression level of NRPs relative by optical density to beta2-microglobulin. The authors also investigated VEGF-A isoforms, their receptors, and the clinical implications. Vascularity of NSCLC was morphologically estimated on sections immunostained with anti-CD34 antibody.

RESULTS

Eleven of 15 extraneoplastic specimens showed NRP1 expression (73.3%) and 8 showed NRP2 expression (53.3%). The expression level of NRP1 or NRP2 of neoplasmic tissue was higher than that of extraneoplastic tissues (P < 0.01, Mann-Whitney U test). Fifty-five and 44 NSCLCs expressed NRP1 and NRP2, respectively. Forty patients co-expressing NRP1 and NRP2 showed significantly poorer prognosis and increased vessel counts as compared to those 28 cases without co-expression (P < 0.05, log-rank test; P < 0.05, Mann-Whitney U test).

CONCLUSIONS

The co-expression of NRP1 and NRP2 genes is significantly correlated with tumor progression through neovascularization in NSCLC. These results suggest that both NRP1 and NRP2 are key molecules for stromal vascularization by cell-retained VEGF in NSCLC.

PLEXIN-D1, a novel plexin family member, is expressed in vascular endothelium and the central nervous system during mouse embryogenesis

The genetic defect in Möbius syndrome 2 (MBS2, MIM 601471), a dominantly inherited disorder characterised by paralysis of the facial nerve, is situated at chromosome 3q21-q22. We characterised the cDNA and predicted protein, and examined the expression pattern during mouse embryogenesis of a positional candidate gene, PLEXIN-D1 (PLXND1). The cDNA for PLXND1 is 7095 base pairs in length, coding for a predicted protein of 1925 amino acids. The protein features all known domains of plexin family members, with the exception of the third Met-related sequence. Northern analysis revealed a very low expression of PLXND1 in adult mouse and adult human tissues. To investigate the expression of PlxnD1 during embryogenesis, RNA in situ hybridisation was performed on mouse embryos from various stages. This investigation revealed expression of PlxnD1 in cells from the central nervous system (CNS) and in vascular endothelium. Early expression in the CNS is located in the ganglia, cortical plate of the cortex, and striatum. At later embryologic stages, neural expression was also seen in the external granular layer of the cerebellum and several nerve nuclei. The expression in the vascular system resides solely in the endothelial cells of developing blood vessels. Based on our results, we suggest that this expression of a member of the plexin family in vascular endothelium could point toward a role in embryonic vasculogenesis.

Abnormal lymphatic vessel development in neuropilin 2 mutant mice

Neuropilin 2 is a receptor for class III semaphorins and for certain members of the vascular endothelial growth factor family. Targeted inactivation of the neuropilin 2 gene (Nrp2) has previously shown its role in neural development. We report that neuropilin 2 expression in the vascular system is restricted to veins and lymphatic vessels. Homozygous Nrp2 mutants show absence or severe reduction of small lymphatic vessels and capillaries during development. This correlated with a reduction of DNA synthesis in the lymphatic endothelial cells of the mutants. Arteries, veins and larger, collecting lymphatic vessels developed normally, suggesting that neuropilin 2 is selectively required for the formation of small lymphatic vessels and capillaries.

Neuropilin-1 is differentially expressed in myoepithelial cells and vascular smooth muscle cells in preneoplastic and neoplastic human breast: a possible marker for the progression of breast cancer

The expression and distribution of neuropilin-1 (NRP-1) was examined in the samples of normal human breast tissues and in non-neoplastic and neoplastic areas of breast tissue removed for carcinoma using RT-PCR as well as conventional and tissue microarrays immunohistochemical analyses. The NRP-1 mRNA expression was significantly higher in neoplastic tissues as compared to normal breast samples. Immunohistochemically, the myoepithelial cells of the mammary ducts and lobules display positive reactions for NRP-1, whereas the inner ductal and lobular epithelial cell layers failed to react. The myoepithelial cells of ducts and lobules in both neoplastic and non-neoplastic tissue specimens displayed a stronger positive reaction for NRP-1 than those in the normal breast. A positive reaction for NRP-1, but with a gradual reduction in intensity, was observed in the myoepithelial cells of ducts with atypical epithelial hyperplasia and ductal carcinoma in situ (DCIS). The reaction was undetected or minimally detected in the areas of invasive carcinoma. NRP-1 positive immunolabeling was also localized in the vascular smooth muscle cells and in some endothelial cells of the blood vessels in normal, non-neoplastic and neoplastic breast tissue samples. In areas of breast carcinoma, NRP-1 immunolabeling was more prominent in both vascular smooth muscle cells and in some endothelial cells than in similar cells in normal breast. The specificity of the newly developed antibody for NRP-1 was confirmed by in situ hybridization with DIG-labeled PCR generated probe. These results suggest that NRP-1 may be a multiple function protein in human breast and may be involved in the induction of local invasiveness of neoplasia and angiogenesis and have direct relevance to the progression of breast cancer.

Expression of Vema in the developing mouse spinal cord and optic chiasm

A critical phase of nervous system development is the formation of connections between axons and their synaptic targets. Intermediate targets play important roles in axon pathfinding by supplying growing axons with long- and short- range guidance cues at decision points along their trajectory. We recently identified Vema as a novel membrane-associated protein that is expressed at the ventral midline of the developing vertebrate central nervous system (CNS). We report that Vema is expressed in the floor plate, an intermediate target for pathfinding commissural axons located at the ventral midline of the developing mouse spinal cord. Interestingly, Vema expression overlaps with the position of an unique population of neurons situated at the midline of the ventral diencephalon and that function as intermediate targets for pathfinding retinal ganglion cell axons. The distribution of Vema in the developing spinal cord and optic chiasm resembles the expression patterns of a variety of molecules known to play important roles in axon guidance, including Robo2, Neuropilin2, and SSEA. The expression of Vema at two key choice points for pathfinding axons suggests an important role for this protein in regulating axon guidance at the midline of the developing mouse central nervous system.

Neuropilin-2 is a novel marker expressed in pancreatic islet cells and endocrine pancreatic tumours

Neuropilin-2 (NP-2) is a cell surface transmembrane protein originally characterized as a receptor for the type 3 semaphorins, and more recently for a number of vascular endothelial growth factor (VEGF) isoforms. NP-2 expression has been recently localized to a subset of neuroendocrine cells in the gastrointestinal tract. The aim of this study was to define the expression pattern of NP-2 in normal pancreatic islets and to determine the utility of NP-2 expression as a diagnostic marker of pancreatic endocrine tumours. Paraffin-embedded tissue sections from 30 endocrine pancreatic tumours (EPTs) and from normal pancreas were immunostained with a rabbit polyclonal antibody generated towards NP-2. Nineteen of the tumours were hormonally functional (nine insulinomas, nine gastrinomas, and one glucagonoma). The NP-2 staining pattern was correlated with islet cell hormone expression. In addition, NP-2 expression was evaluated in other normal neuroendocrine tissues and neuroendocrine neoplasms. In normal pancreas, NP-2 stained a distinct subset of islet cells situated primarily at the islet periphery. Double immunohistochemical staining revealed co-localization with glucagon-expressing cells. Moderate to strong NP-2 staining was present in 27 of 30 EPTs. Serial staining of the pancreatic tumours with insulin, gastrin, glucagon, pancreatic polypeptide (PP) or somatostatin did not reveal a distinct pattern of co-localization. NP-2 expression was not detected in neuroendocrine cells outside the gastroenteropancreatic system, or in their corresponding neoplasms, except for focal staining in one bronchial carcinoid tumour. In conclusion, the vast majority of EPTs examined expressed NP-2, suggesting its utility as a diagnostic marker for these tumours. The function of NP-2 in islet cell biology or tumourigenesis remains to be elucidated.

Directional guidance of oligodendroglial migration by class 3 semaphorins and netrin-1

Oligodendrocytes, the myelin-forming cells of the CNS, are generated from multiple foci distributed along the developing neural tube. Little is known about the endogenous guidance cues controlling the migration of oligodendrocyte precursor cells (OPCs) from their site of emergence toward their final destination, mainly the future white matter tracts. During embryonic development, the optic nerve is populated by OPCs originating in the diencephalon that migrate from the chiasm toward the retina. Here we show that OPCs migrating into the embryonic optic nerve express the semaphorin receptors neuropilin-1 and -2, as well as deleted in colorectal cancer (DCC) and, to a lesser extend unc5H1, two of the netrin-1 receptors. Using a functional migration assay, we provide evidence that Sema 3A and netrin-1 exert opposite chemotactic effects, repulsive or attractive, respectively, on embryonic OPCs. In addition, we show that Sema 3F has a dual effect, chemoattractive and mitogenic on embryonic OPCs. The localization of cells expressing Sema 3A, Sema 3F, and netrin-1 is consistent with a role for these ligands in the migration of OPCs in the embryonic optic nerve. Altogether, our results suggest that the migration of OPCs in the embryonic optic nerve is modulated by a balance of effects mediated by members of the semaphorin and netrin families.

Neuropilin-1 is required for vascular development and is a mediator of VEGF-dependent angiogenesis in zebrafish

Neuropilin-1 (NRP1) is a cell-surface receptor for both vascular endothelial growth factor(165) (VEGF(165)) and class 3 semaphorins that is expressed by neurons and endothelial cells. NRP1 is required for normal developmental angiogenesis in mice. The zebrafish is an excellent system for analyzing vascular development. Zebrafish intersegmental vessels correspond to mammalian capillary sprouts, whereas the axial vessels correspond to larger blood vessels, such as arteries. The zebrafish NRP1 gene (znrp1) was isolated and when overexpressed in cells, zNRP1 protein was a functional receptor for human VEGF(165). Whole-mount in situ hybridization showed that transcripts for znrp1 during embryonic and early larval development were detected mainly in neuronal and vascular tissues. Morpholino-mediated knockdown of zNRP1 in embryos resulted in vascular defects, most notably impaired circulation in the intersegmental vessels. Circulation via trunk axial vessels was not affected. Embryos treated with VEGF receptor-2 kinase inhibitor had a similar intersegmental vessel defect suggesting that knockdown of zNRP1 reduces VEGF activity. To determine whether NRP1 and VEGF activities were interdependent in vivo, zNRP1 and VEGF morpholinos were coinjected into embryos at concentrations that individually did not significantly inhibit blood vessel development. The result was a potent inhibition of blood cell circulation via both intersegmental and axial vessels demonstrating that VEGF and NRP1 act synergistically to promote a functional circulatory system. These results provide the first physiological demonstration that NRP1 regulates angiogenesis through a VEGF-dependent pathway.

Neuropilin-1 binds vascular endothelial growth factor 165, placenta growth factor-2, and heparin via its b1b2 domain

Neuroplin-1 (NRP1), a receptor for vascular endothelial growth factor (VEGF) family members, has three distinct extracellular domains, a1a2, b1b2, and c. To determine the VEGF(165) and placenta growth factor 2 (PlGF-2)-binding sites of NRP1, recombinant NRP1 domains were expressed in mammalian cells as Myc-tagged, soluble proteins, and used in co-precipitation experiments with 125I-VEGF165 and 125I-PlGF-2. Anti-Myc antibodies immunoprecipitated 125I-VEGF165 and 125I-PlGF-2 in the presence of the b1b2 but not of the a1a2 and c domains. Neither b1 nor b2 alone was capable of binding 125I-VEGF165. In competition experiments, VEGF165 competed PlGF-2 binding to the NRP1 b1b2 domain, suggesting that the binding sites of VEGF165 and PlGF-2 overlap. The presence of the a1a2 domain greatly enhanced VEGF165, but not PlGF-2 binding to b1b2. Heparin enhanced the binding of both 125I-VEGF165 and 125I-PlGF-2 to the b1b2 domain by 20- and 4-fold, respectively. A heparin chain of at least 20-24 monosaccharides was necessary for binding. In addition, the b1b2 domain of NRP1 could bind heparin directly, requiring heparin oligomers of at least 8 monosaccharide units. It was concluded that an intact b1b2 domain serves as the VEGF165-, PlGF-2-, and heparin-binding sites in NRP1, and that heparin is a critical component for regulating VEGF165 and PlGF-2 interactions with NRP1 by physically interacting with both receptor and ligands.

Aberrant sensory innervation of the olfactory bulb in neuropilin-2 mutant mice

The mammalian olfactory system consists of two anatomically segregated structures, the main olfactory system and the vomeronasal system, which each detect distinct types of chemical stimuli in the environment. During development, sensory neurons establish precise axonal connections with their respective targets within the olfactory bulb. The specificity of the odorant or vomeronasal receptor expressed by the sensory neuron is crucial in this process, yet it is less clear which of the more conventional axon guidance molecules are involved. Here, we show that neuropilin-2, a coreceptor for some of the class 3 semaphorins, is expressed in subpopulations of olfactory and vomeronasal sensory neurons. We generated a knock-out mutation in the neuropilin-2 gene by gene targeting in embryonic stem cells. Neuropilin-2 mutant mice exhibit profound and distinct effects on target innervation within the olfactory bulb. In the main olfactory system, axons of olfactory sensory neurons penetrate into the deeper layers of the main olfactory bulb. In the vomeronasal system, axonal fasciculation within the vomeronasal nerve is affected; some axons are misrouted and innervate glomeruli in an ectopic domain of the accessory olfactory bulb.

A neuronal receptor, neuropilin-1, is essential for the initiation of the primary immune response

The initiation of a primary immune response requires contact between dendritic cells (DCs) and resting T cells. However, little is known about the proteins that mediate this initial contact. We show here that neuropilin-1, a receptor involved in axon guidance, was expressed by human DCs and resting T cells both in vitro and in vivo. The initial contact between DCs and resting T cells led to neuropilin-1 polarization on T cells. DCs and resting T cells specifically bound soluble neuropilin-1, and resting T cells formed clusters with neuropilin-1-transfected COS-7 cells in a neuropilin-1-dependent manner. Functionally, preincubation of DCs or resting T cells with blocking neuropilin-1 antibodies inhibited DC-induced proliferation of resting T cells. These data suggest that neuropilin-1 mediates interactions between DCs and T cells that are essential for initiation of the primary immune response and show parallels between the nervous and immune systems.

Semaphorin 1a and semaphorin 1b are required for correct epidermal cell positioning and adhesion during morphogenesis in C. elegans

The semaphorin family comprises secreted and transmembrane proteins involved in axon guidance and cell migration. We have isolated and characterized deletion mutants of C. elegans semaphorin 1a (Ce-sema-1a or smp-1) and semaphorin 1b (Ce-sema-1b or smp-2) genes. Both mutants exhibit defects in epidermal functions. For example, the R1.a-derived ray precursor cells frequently fail to change anterior/posterior positions completely relative to their sister tail lateral epidermal precursor cell R1.p, causing ray 1 to be formed anterior to its normal position next to ray 2. The ray cells, which normally separate from the lateral tail seam cell (SET) at the end of L4 stage, remains connected to the SET cell even in adult mutant males. The ray 1 defects are partially penetrant in each single Ce-sema-1 mutant at 20°C, but are greatly enhanced in Ce-sema-1 double mutants, suggesting that Ce-Sema-1a and Ce-Sema-1b function in parallel to regulate ray 1 position. Both mutants also have defects in other aspects of epidermal functions, including head and tail epidermal morphogenesis and touch cell axon migration, whereas, smp-1 mutants alone have defects in defecation and brood size. A feature of smp-1 mutants that is shared with mutants of mab-20 (which encodes Sema-2a) is the abnormal perdurance of contacts between epidermal cells.

Injury-induced class 3 semaphorin expression in the rat spinal cord

In this study we evaluate the expression of all members of the class 3 semaphorins and their receptor components following complete transection and contusion lesions of the adult rat spinal cord. Following both types of lesions the expression of all class 3 semaphorins is induced in fibroblast in the neural scar. The distribution of semaphorin-positive fibroblasts differs markedly in scars formed after transection or contusion lesion. In contusion lesions semaphorin expression is restricted to fibroblasts of the meningeal sheet surrounding the lesion, while after transection semaphorin-positive fibroblast penetrate deep into the center of the lesion. Two major descending spinal cord motor pathways, the cortico- and rubrospinal tract, continue to express receptor components for class 3 semaphorins following injury, rendering them potentially sensitive to scar-derived semaphorins. In line with this we observed that most descending spinal cord fibers were not able to penetrate the semaphorin positive portion of the neural scar formed at the lesion site. These results suggest that the full range of secreted semaphorins contributes to the inhibitory nature of the neural scar and thereby may inhibit successful regeneration in the injured spinal cord. Future studies will focus on the neutralization of class 3 semaphorins, in order to reveal whether this creates a more permissive environment for regeneration of injured spinal cord axons.

Caenorhabditis elegansPlexinA, PLX-1, interacts with transmembrane semaphorins and regulates epidermal morphogenesis

The plexin family transmembrane proteins are putative receptors for semaphorins, which are implicated in the morphogenesis of animal embryos, including axonal guidance. We have generated and characterized putative null mutants of the C. elegans plexinA gene, plx-1. plx-1 mutants exhibited morphological defects: displacement of ray 1 and discontinuous alae. The epidermal precursors for the affected organs were aberrantly arranged in the mutants, and a plx-1::gfp transgene was expressed in these epidermal precursor cells as they underwent dynamic morphological changes. Suppression of C. elegans transmembrane semaphorins, Ce-Sema-1a and Ce-Sema-1b, by RNA interference caused a displacement of ray 1 similar to that of plx-1 mutants, whereas mutants for the Ce-Sema-2a/mab-20 gene, which encodes a secreted-type semaphorin, exhibited phenotypes distinct from those of plx-1 mutants. A heterologous expression system showed that Ce-Sema-1a, but not Ce-Sema-2a, physically bound to PLX-1. Our results indicate that PLX-1 functions as a receptor for transmembrane-type semaphorins, and, though Ce-Sema-2a and PLX-1 both play roles in the regulation of cellular morphology during epidermal morphogenesis, they function rather independently.

Significant up-regulation of a novel gene, CLCP1, in a highly metastatic lung cancer subline as well as in lung cancers in vivo

Most lung cancer patients are unfortunately uncurable and die because of widespread metastases, thus indicating the importance of identification of molecules with a crucial role in this process. Our previous expression profiling analysis of a highly metastatic lung cancer cell line, NCI-H460-LNM35, and its parental low metastatic line, NCI-H460-N15, revealed significant up-regulation of both known and unknown genes in LNM35. In this study, we describe the isolation and detailed characterizations of a novel gene, named CLCP1, which corresponds to one of such expression sequence tags with up-regulated expression in LNM35. The CLCP1 gene was found to encode a protein with 775 amino acids with structural similarities to, but distinct from neuropilins, cell surface receptors for VEGF165 and semaphorins. Notably, CLCP1 was shown to be up-regulated not only in LNM35 in association with its acquisition of metastatic phenotype during in vivo selection, but also in a significant fraction of lung cancers in vivo with high frequency in metastatic lesions, warranting future studies for a better understanding of the molecular mechanisms of lung cancer metastasis.

Global analysis of gene expression patterns in developing mouse neocortex using serial analysis of gene expression

Molecular inventories of the developing mouse neocortex before and after birth were generated using the global gene expression profiling tool serial analysis of gene expression (SAGE). Libraries were generated from embryonic day 15 and postnatal day 1 mouse neocortex and more than 40,000 tags were collected (20,211 and 22,001 tags, representing 11,706 and 12,402 transcripts, respectively). Comparison of the two libraries resulted in the identification of 321 transcripts that were differentially expressed (P < 0.05). Differential expression was independently verified for selected genes by Northern blotting, and in situ hybridization revealed spatial expression patterns in the neocortex. Differentially expressed transcripts included genes known to be important in neocortical development (e.g., brain factor 1, neuroD2, and Id2), genes not previously associated with neocortical development (such as brahma-related gene 1, receptor for activated C-kinase I, hypermethylated in cancer 2, and Evi9), and genes of unknown identity or function.

Neuropilin-2 mediates axonal fasciculation, zonal segregation, but not axonal convergence, of primary accessory olfactory neurons

The mechanisms that underlie axonal pathfinding of vomeronasal neurons from the vomeronasal organ (VNO) in the periphery to select glomeruli in the accessory olfactory bulb (AOB) are not well understood. Neuropilin-2, a receptor for secreted semaphorins, is expressed in V1R- and V3R-expressing, but not V2R-expressing, postnatal vomeronasal neurons. Analysis of the vomeronasal nerve in neuropilin-2 (npn-2) mutant mice reveals pathfinding defects at multiple choice points. Vomeronasal sensory axons are severely defasciculated and a subset innervates the main olfactory bulb (MOB). While most axons of V1R-expressing neurons reach the AOB and converge into distinct glomeruli in stereotypic locations, they are no longer restricted to their normal anterior AOB target zone. Thus, Npn-2 and candidate pheromone receptors play distinct and complementary roles in promoting the wiring and patterning of sensory neurons in the accessory olfactory system.

Knowing how to navigate: mechanisms of semaphorin signaling in the nervous system

Neuronal connections are made during embryonic development with astonishing precision to ultimately form the physical basis for the central nervous system's main capacity: information processing. Over the past few decades, much has been learned about the general principles of axon guidance. A key finding to emerge is that extracellular cues play decisive roles in establishing the connections. One family of such cues, the semaphorin proteins, was first identified as repellents for navigating axons during brain wiring. Recent studies have implicated these molecules in many other processes of neuronal development, including axonal fasciculation, target selection, neuronal migration, and dendritic guidance, as well as in the remodeling and repair of the adult nervous system. It appears that responding neuronal processes sense these semaphorin signals by a family of transmembrane molecules, namely the plexins, even though neuropilins were also found to be required for mediating the interaction between plexins and class 3 semaphorins. Our understanding of the intracellular signaling machinery linking the receptors to the cytoskeleton machinery is still incomplete, but several molecules have been implicated in mediating or modulating semaphorin-induced responses. Adding to the complexity of semaphorin biology, new findings implicate semaphorins in functioning not only as signaling ligands, but also as signal-transducing receptors. Thus, semaphorins may serve as important probes for exploring the mechanisms of intercellular communication during the development and function of the nervous system.