Identification of a member of mouse semaphorin family

Semaphorin 3A-hypoxia inducible factor 1 subunit alpha co-overexpression enhances the osteogenic differentiation of induced pluripotent stem cells-derived mesenchymal stem cells in vitro

Background:

Mesenchymal stem or stromal cells (MSCs) derived from the induced pluripotent stem cells (iPSCs) have uniform biological activity, which makes the clinical application of MSCs in bone repair possible. Culturing the iPSC-MSCs onto osteoconductive materials is a promising tissue engineering-based strategy in bone regeneration. The aim of this work was to evaluate the effects of semaphorin 3A (Sema3A) and hypoxia inducible factor 1 subunit alpha (HIF1α) co-overexpression on the survival and osteogenic differentiation of iPSC-MSCs.

Methods:

Sema3A and HIF1α were linked together with the three (GGGGS; G, glycine; S, serine) peptide fragment, and their co-expression in iPSC-MSCs was mediated by a lentiviral vector. The fusion protein retained the immune reactivity for both Sema3A and HIF1α as determined with Western blotting. iPSC-MSCs were infected with overexpression lentivirus (oeLenti) as negative control, oeLenti-Sema3A, oeLenti-HIF1α or oeLenti-Sema3A-HIF1α lentiviruses.

Results:

Sema3A overexpression alone promoted the osteogenic differentiation of iPSC-MSCs (the activity and/or expression of osteoblast markers, such as alkaline phosphatase, osteopontin, and osteocalcin, were upregulated), and suppressed cell survival. The Sema3A-HIF1α fusion protein showed a comparable osteoconductive effect to that of Sema3A without reducing cell survival. We further seeded iPSC-MSCs modified by SemaA-HIF1α overexpression onto hydroxyapatite (HA) scaffolds, and evaluated their growth and differentiation on this three-dimensional material. Additional data indicated that, as compared to iPSC-MSCs cultured in ordinary two-dimensional dishes, cells cultured in HA scaffolds grew (blank vs. HA scaffolds: 0.83 vs. 1.39 for survival) and differentiated better (blank vs. HA scaffolds: 11.29 vs. 16.62 for alkaline phosphatase activity).

Conclusion:

Modifying iPSC-MSCs with pro-osteogenic (Sema3A) and pro-survival (HIF1α) factors may represent a promising strategy to optimize tissue engineering-based strategy in bone repair.

Sema3A and HIF1α co-overexpressed iPSC-MSCs/HA scaffold facilitates the repair of calvarial defect in a mouse model

Mesenchymal stem/stromal cells (MSCs) play an important role in bone tissue engineering because MSCs possess multilineage potential of differentiation to mesenchymal tissues. Semaphorin 3A (Sema3A) and hypoxia-inducible factor-1α (HIF1α) are proved as important regulatory factors for osteogenesis and angiogenesis. The aim of this study was to investigate the effects of Sema3A and HIF1α co-overexpression on the osteogenesis and angiogenesis in induced pluripotent stem cell-derived mesenchymal stem cells (iPSC-MSCs). Importantly, we assessed the potential osteogenic effectiveness of Sema3A and HIF1α co-overexpressed iPSC-MSCs seeded on hydroxyapatite (HA) scaffold in a mouse calvarial defect model. The overexpression for Sema3A, HIF1α, or Sema3A-HIF1α fusion in iPSC-MSCs was performed by separately infecting with conducted lentiviral vector. We determined the cell proliferation, the expressions of osteogenic, and endothelial markers of iPSC-MSCs cultured in osteogenic or endothelial induction medium in vitro. A mouse model calvarial defect was created and implanted with the Empty implant, HA scaffold alone, HA scaffold combined with iPSC-MSCs that infected with negative control or Sema3A-HIF1α fusion for 8 weeks in vivo. The results showed that Sema3A and HIF1α co-overexpression reversed the reduced cell proliferation that reduced by Sema3A overexpression alone. Importantly, the co-overexpression significantly increased the expressions of osteogenic and angiogenic related-genes compared with negative control after induction. Moreover, the Sema3A-HIF1α co-overexpressed iPSC-MSCs seeded on HA scaffold boosted the new bone and collagen fiber formation and facilitated repair of calvarial defect in a mouse model, which might have the potential application for bone defect reconstruction.

Sema4C mediates EMT inducing chemotherapeutic resistance of miR-31-3p in cervical cancer cells

Sema4C, the target of many miRNAs, is involved in EMT-mediated chemotherapeutic resistance of many malignant tumors. However, the underlying upstream regulatory mechanisms of Sema4C-induced EMT and Sema4C-mediated drug resistance are still unclear. The aim of this study was to explore the potential role of miR-31-3p/Sema4C in regulating EMT in cisplatin-resistant (CR) cervical cancer cells. High expression levels of Sema4C were more frequently found in cervical cancer tissues and were associated with poor prognosis, whereas miR-31-3p was significantly downregulated in cervical cancer tissues, which was associated with shorter disease-free and overall survival. Overexpression of miR-31-3p inhibited malignant behaviors and EMT of cervical cancer cells in vitro. Furthermore, miR-31-3p was identified to directly target Sema4C, and upregulation of miR-31-3p reversed EMT-mediated biological functions, including cisplatin resistance of Sema4C in cervical cancer cells. These results suggest that Sema4C promoted EMT-mediated cisplatin resistance in cervical cancer cells and that this effect was inhibited by overexpression of miR-31-3p. Thus, silencing Sema4C or overexpression of miR-31-3p could be a novel approach to treat drug resistance to chemotherapy in cervical cancers.

Identification of Differentially Expressed Genes through Integrated Study of Alzheimer's Disease Affected Brain Regions

Background

Alzheimer’s disease (AD) is the most common form of dementia in older adults that damages the brain and results in impaired memory, thinking and behaviour. The identification of differentially expressed genes and related pathways among affected brain regions can provide more information on the mechanisms of AD. In the past decade, several studies have reported many genes that are associated with AD. This wealth of information has become difficult to follow and interpret as most of the results are conflicting. In that case, it is worth doing an integrated study of multiple datasets that helps to increase the total number of samples and the statistical power in detecting biomarkers. In this study, we present an integrated analysis of five different brain region datasets and introduce new genes that warrant further investigation.

Methods

The aim of our study is to apply a novel combinatorial optimisation based meta-analysis approach to identify differentially expressed genes that are associated to AD across brain regions. In this study, microarray gene expression data from 161 samples (74 non-demented controls, 87 AD) from the Entorhinal Cortex (EC), Hippocampus (HIP), Middle temporal gyrus (MTG), Posterior cingulate cortex (PC), Superior frontal gyrus (SFG) and visual cortex (VCX) brain regions were integrated and analysed using our method. The results are then compared to two popular meta-analysis methods, RankProd and GeneMeta, and to what can be obtained by analysing the individual datasets.

Results

We find genes related with AD that are consistent with existing studies, and new candidate genes not previously related with AD. Our study confirms the up-regualtion of INFAR2 and PTMA along with the down regulation of GPHN, RAB2A, PSMD14 and FGF. Novel genes PSMB2, WNK1, RPL15, SEMA4C, RWDD2A and LARGE are found to be differentially expressed across all brain regions. Further investigation on these genes may provide new insights into the development of AD. In addition, we identified the presence of 23 non-coding features, including four miRNA precursors (miR-7, miR570, miR-1229 and miR-6821), dysregulated across the brain regions. Furthermore, we compared our results with two popular meta-analysis methods RankProd and GeneMeta to validate our findings and performed a sensitivity analysis by removing one dataset at a time to assess the robustness of our results. These new findings may provide new insights into the disease mechanisms and thus make a significant contribution in the near future towards understanding, prevention and cure of AD.

Semaphorin 4C and 4G are ligands of Plexin-B2 required in cerebellar development

Semaphorins and Plexins are cognate ligand-receptor families that regulate important steps during nervous system development. The Plexin-B2 receptor is critically involved in neural tube closure and cerebellar granule cell development, however, its specific ligands have only been suggested by in vitro studies. Here, we show by in vivo and in vitro analyses that the two Semaphorin-4 family members Sema4C and Sema4G are likely to be in vivo ligands of Plexin-B2. The Sema4C and Sema4G genes are expressed in the developing cerebellar cortex, and Sema4C and Sema4G proteins specifically bind to Plexin-B2 expressing cerebellar granule cells. To further elucidate their in vivo function, we have generated and analyzed Sema4C and Sema4G knockout mouse mutants. Like Plexin-B2-/- mutants, Sema4C-/- mutants reveal exencephaly and subsequent neonatal lethality with partial penetrance. Sema4C-/- mutants that bypass exencephaly are viable and fertile, but display distinctive defects of the cerebellar granule cell layer, including gaps in rostral lobules, fusions of caudal lobules, and ectopic granule cells in the molecular layer. In addition to neuronal defects, we observed in Sema4C-/- mutants also ventral skin pigmentation defects that are similar to those found in Plexin-B2-/- mutants. The Sema4G gene deletion causes no overt phenotype by itself, but combined deletion of Sema4C and Sema4G revealed an enhanced cerebellar phenotype. However, Sema4C/Sema4G double mutants showed overall less severe cerebellar phenotypes than Plexin-B2-/- mutants, indicating that further ligands of Plexin-B2 exist. In explant cultures of the developing cerebellar cortex, Sema4C promoted migration of cerebellar granule cell precursors in a Plexin-B2-dependent manner, supporting the model that a reduced migration rate of granule cell precursors is the basis for the cerebellar defects of Sema4C-/- and Sema4C/Sema4G mutants.

Semaphorin signaling in vascular and tumor biology

The neuropilins were originally characterized as cell membrane receptors that bind axon guidance factors belonging to the class-3 semaphorin subfamily. To transduce semaphorin signals, they form complexes with members of the plexin receptor family in which neuropilins serve as the ligand binding components and the plexins as the signal transducing components. The neuropilins were subsequently found to double as receptors for specific heparin binding splice forms of vascular endothelial growth factor (VEGF), and to be expressed on endothelial cells. This finding suggested that semaphorins may function as modulators of angiogenesis. It was recently found that several types of semaphorins such as semaphorin-3F function as inhibitors of angiogenesis while others, most notably semaphorin-4D, function as angiogenic factors. Furthermore, semaphorins such as semaphorin-3F and semaphorin-3B have been characterized as tumor suppressors and have been found to exert direct effects upon tumor cells. In this chapter we cover recent developments in this rapidly developing field of research.

Sema4C participates in myogenic differentiation in vivo and in vitro through the p38 MAPK pathway

Sema4C is a member of transmembrane semaphorin proteins which regulate axonal guidance in the developing nervous system. The expression of Sema4C was dramatically induced not only during differentiation of C2C12 mouse myoblasts, but also during injury-induced skeletal muscle regeneration. C2C12 cells stably or transiently expressing Sema4C both showed increased myogenic differentiation reflected by accelerated myotube formation and expression of muscle-specific proteins. Overexpression of Sema4C elicited p38 phosphorylation directly, and the effects of Sema4C during myogenic differentiation could be abolished by the p38alpha-specific inhibitor SB203580. Knockdown of Sema4C by siRNA transfection during C2C12 myoblasts differentiation could suppress the phosphorylation of p38 followed by dramatically diminished myotube formation. Sema4C could activate the myogenin promoter during myogenic differentiation. This activation could be abolished by p38 inhibitor SB203580. Taken together, these observations reveal novel functional potentialities of Sema4C which suggest that Sema4C promotes terminal myogenic differentiation in a p38 MAPK-dependent manner.

Immunosuppressive role of semaphorin-3A on T cell proliferation is mediated by inhibition of actin cytoskeleton reorganization

Timely negative regulation of the immune system is critical to allow it to perform its duty while maintaining it under tight control to avoid overactivation. We previously reported that the neuronal receptor neuropilin-1 (NP-1) is expressed in human lymph nodes. However, the role of NP-1 interaction with its physiological ligand semaphorin-3A (Sema-3A) on immune cells remains elusive. Here we show that Sema-3A is expressed by activated DC and T cells, and that its secretion in DC/T cell cocultures is delayed. Sema-3A/NP-1 interaction down-modulated T cell activation since addition of Sema-3A in DC/T cell cocultures dramatically inhibited allogeneic T cell proliferation. More importantly, neutralization by blocking antibodies or by antagonist peptide of endogenous Sema-3A produced by DC/T cell cocultures resulted in a 130% increase in T cell proliferation. Sema-3A acted directly on T cells, since it could block anti-CD3/CD28-stimulated proliferation of T cells. Finally, immunomodulatory functions of Sema-3A relied on the blockage of actin cytoskeleton reorganization, affecting TCR polarization and interfering with early TCR signal transduction events such as ZAP-70 or focal adhesion kinase phosphorylation. Therefore, we propose that Sema-3A secretion and the resulting NP-1/Sema-3A interaction are involved in a late negative feedback loop controlling DC-induced T cell proliferation.

A novel locus (RP33) for autosomal dominant retinitis pigmentosa mapping to chromosomal region 2cen-q12.1

Retinitis pigmentosa (RP) is a heterogeneous group of progressive degenerative disorders of the retina with a strong genetic component. Here, we report the clinical and genetic findings in a Chinese family in which autosomal dominant RP (adRP) was inherited by 13 affected members in four generations. Using a genome-wide linkage screening approach, a novel disease locus (RP33) was assigned to the long arm of chromosome 2. A maximum multi-point LOD score of 4.69 was reached at marker D2S2222 in 2q11.2. Meiotic recombination events in affected members placed RP33 in a 15.5 cM region between D2S329 and D2S2229. From meiotic recombinations in two unaffected members RP33 was further refined to a 4.8 cM (9.5 Mb) interval flanked by D2S2159 and D2S1343 in chromosomal region 2cen-q12.1. No disease-associated mutations were detected in the candidate genes SEMA4C, CNGA3 or HNK1ST from within the region. MERTK, a known disease gene for autosomal recessive RP located close to RP33 was similarly excluded. Clinically, the family presented relatively late onset of night blindness, gradually decreased visual acuity, progressive loss of peripheral visual field and typical RP fundus changes in the mid-periphery of the retina. In conclusion, a novel locus for adRP has been assigned to chromosomal region 2cen-q12.1, which in the present kindred was associated with a relatively late onset form of the disease.

The semaphorins

Semaphorins are secreted, transmembrane, and GPI-linked proteins, defined by cysteine-rich semaphorin protein domains, that have important roles in a variety of tissues. Humans have 20 semaphorins, Drosophila has five, and two are known from DNA viruses; semaphorins are also found in nematodes and crustaceans but not in non-animals. They are grouped into eight classes on the basis of phylogenetic tree analyses and the presence of additional protein motifs. The expression of semaphorins has been described most fully in the nervous system, but they are also present in most, or perhaps all, other tissues. Functionally, semaphorins were initially characterized for their importance in the development of the nervous system and in axonal guidance. More recently, they have been found to be important for the formation and functioning of the cardiovascular, endocrine, gastrointestinal, hepatic, immune, musculoskeletal, renal, reproductive, and respiratory systems. A common theme in the mechanisms of semaphorin function is that they alter the cytoskeleton and the organization of actin filaments and the microtubule network. These effects occur primarily through binding of semaphorins to their receptors, although transmembrane semaphorins also serve as receptors themselves. The best characterized receptors for mediating semaphorin signaling are members of the neuropilin and plexin families of transmembrane proteins. Plexins, in particular, are thought to control many of the functional effects of semaphorins; the molecular mechanisms of semaphorin signaling are still poorly understood, however. Given the importance of semaphorins in a wide range of functions, including neural connectivity, angiogenesis, immunoregulation, and cancer, much remains to be learned about these proteins and their roles in pathology and human disease.

Requirement of the transmembrane semaphorin Sema4C for myogenic differentiation

Semaphorins constitute a large family of signaling proteins that contribute to axonal guidance. Here we demonstrate that the transmembrane semaphorin Sema4C is up-regulated both in the early stage of differentiation of C2C12 mouse skeletal myoblasts into myotubes and during injury-induced muscle regeneration in vivo. Depletion of Sema4C in C2C12 cells resulted in marked attenuation of myotube formation. A fusion protein containing the extracellular Sema domain and a peptide corresponding to the intracellular COOH-terminal region of Sema4C each inhibited the differentiation of C2C12 cells. These findings indicate that Sema4C-mediated interaction among myoblasts plays an important role in terminal myogenic differentiation.

Cocaine-induced expression changes of axon guidance molecules in the adult rat brain

Administration of drugs of abuse induces strong molecular adaptations and plasticity within the mesolimbic dopamine (DA) system, a pathway essential for reward-seeking behavior. Little is known about the specific targets involved in this neuroadaptation process, but there are indications that cocaine and other drugs of abuse share the ability to alter the morphology of neuronal dendrites and spines, the primary site of excitatory synapses in the brain. Axon guidance molecules, the very molecular cues that regulate the formation of axon-target connections during development, may mediate these alterations. To test this hypothesis, we investigated mRNA expression changes of 39 axon guidance molecules, including 17 Semaphorins, 12 Ephs, 8 Ephrins, and 2 neuropilins in the mesolimbic dopamine system of cocaine-treated animals under different paradigms by mean of DNA-Microarray and quantitative real-time PCR. In all cases, strong changes in gene expression are observed, yielding to up or downregulation of these axon guidance molecules. Our data suggest that cocaine treatment induces activation of a complex program of synaptic rearrangements, which may partly recapitulate the plastic changes occurring during development, and may underlie the important neuroplastic adaptations that occur in the reward- and memory-related brain centers following drug action. We conclude that in some brain regions, exposure to psychomotor-stimulant drugs produce expression changes in axon guidance molecules, which may contribute to cognitive deficits associated with drug abuse.

Sema4D stimulates axonal outgrowth of embryonic DRG sensory neurones

Several semaphorins are thought to function as potent inhibitors of axonal growth. We have found that Sema4D stimulates axonal outgrowth of embryonic dorsal root ganglion (DRG) neurones in stead of retraction. Neutralizing antibodies to Sema4D inhibit this action. This action appears to differ slightly from that on PC12 cells, because DRG neurones respond to Sema4D without addition of nerve growth factor (NGF), while PC12 cells do not. On the other hand, it is blocked by deprivation of endogenous NGF with antibodies to NGF and also by Trk-inhibitor K252a, suggesting that endogenously produced-NGF and the activation of Trk receptor are required for Sema4D-action on DRG neurones. These indicate that neurite-outgrowth promoting actions of Sema4D are similar between DRG neurones and PC12 cells, since NGF-Trk signalling are required for these actions. Since Schwann cells can produce NGF, the contamination of these cells in our DRG culture might explain this action. In addition to plexin-B1 that is known as a Sema4D receptor, binding experiments indicate plexin-B2 as another receptor candidate for Sema4D. These plexins and Sema4D are expressed in embryonic DRGs. We suggest a new function of Sema4D as a neurite-outgrowth stimulating, autocrine/paracrine factor in embryonic sensory neurones.

Expression of Dbx1, Neurogenin 2, Semaphorin 5A, Cadherin 8, and Emx1 distinguish ventral and lateral pallial histogenetic divisions in the developing mouse claustroamygdaloid complex

We studied the lateral and ventral pallial divisions of the claustroamygdaloid complex by means of analysis of expression patterns of the developmental regulatory genes Tbr1, Dbx1, Neurogenin 2, Emx1, Cadherin 8, and Semaphorin 5A in mouse developing telencephalon, from embryonic day 12.5 until birth. Our results indicate that these genes help to distinguish distinct lateral and ventral pallial histogenetic divisions in the embryonic telencephalon. Tbr1 is broadly expressed in both lateral and ventral pallial histogenetic divisions (the lateroventral migratory stream plus the mantle) during early and intermediate embryonic development; its signal becomes weak in parts of the mantle during late embryonic development. Dbx1 is strongly and specifically expressed in progenitor cells (ventricular zone) of the ventral pallium during early embryonic development, but there is no signal of this gene in the rest of the pallium nor the subpallium. Neurogenin 2 and Semaphorin 5A are both expressed in a ventral subdivision of the lateroventral migratory stream (called by us the ventral migratory stream). Further, specific nuclei of the claustral complex and pallial amygdala show strong expression of Neurogenin 2 and/or Semaphorin 5A, including the ventromedial claustrum and endopiriform nuclei, the lateral and basomedial amygdalar nuclei, the anterior and posteromedial cortical amygdalar areas, plus the amygdalo-hippocampal area. We interpret these nuclei or areas of the claustroamygdaloid complex as possible derivatives of the ventral pallium. In contrast, during embryonic development the dorsolateral claustrum, the basolateral amygdalar nucleus, and the posterolateral cortical amygdalar area do not express or show weak expression of Neurogenin 2 or Semaphorin 5A, but express selectively and strongly Cadherin 8 plus Emx1, and may be derivatives of the lateral pallium. The lateral pallial and ventral pallial divisions of the claustroamygdaloid complex appear to have some different sets of connections, although this requires further investigation.

In vitro and in vivo characterization of a novel semaphorin 3A inhibitor, SM-216289 or xanthofulvin

SM-216289 (xanthofulvin) isolated from the fermentation broth of a fungal strain, Penicillium sp. SPF-3059, was identified as a strong semaphorin 3A (Sema3A) inhibitor. Sema3A-induced growth cone collapse of dorsal root ganglion neurons in vitro was completely abolished in the presence of SM-216289 at levels less than 2 mum (IC50 = 0.16 mum). When dorsal root ganglion explants were co-cultured with Sema3A-producing COS7 cells in a collagen gel matrix, SM-216289 enabled neurites to grow toward the COS7 cells. SM-216289 diminished the binding of Sema3A to its receptor neuropilin-1 in vitro, suggesting a direct interference of receptor-ligand association. Moreover, our data suggest that SM-216289 interacted with Sema3A directly and blocked the binding of Sema3A to its receptor. We examined the efficacy of SM-216289 in vivo using a rat olfactory nerve axotomy model, in which strong Sema3A induction has been reported around regenerating axons. The regeneration of olfactory nerves was significantly accelerated by a local administration of SM-216289 in the lesion site, suggesting the involvement of Sema3A in neural regeneration as an inhibitory factor. SM-216289 is an excellent molecular probe to investigate the function of Sema3A, in vitro and in vivo, and may be useful for the treatment of traumatic neural injuries.

Effects of neonatal hypothyroidism on the expressions of growth cone proteins and axon guidance molecules related genes in the hippocampus

During critical periods of development, hypothyroidism causes abnormalities of the central nervous system such as incomplete maturation of neuronal and glial cells, reduction in synaptic densities and myelin deficits. In this study expression of development regulated genes, ie transcription of beta-actin, sema 3F, CRMP 1 to 4, GAP-43, G alpha o1, G alpha o2 and translation of beta-actin, G alpha o, G alpha o1, CRMP-2, CRMP-4 genes were examined in the hippocampus of neonatal methimazole induced hypothyroid rats at the age of day 16. All CRMPs mRNA levels were significantly higher in the hypothyroid rats. Significant higher CRMP-2 protein but not CRMP-4 protein was found in the hypothyroid rats. The neonatal experimental hypothyroid states did not affect the protein levels of beta-actin but up-regulate its mRNA. Transcription of CRMP 1 to 4, GAP-43, G alpha o1 but not G alpha o2 and sema 3F was altered by the neonatal treatment. The only sex difference in gene expression was found in the transcription of CRMP-2 gene.

Sema4c, a transmembrane semaphorin, interacts with a post-synaptic density protein, PSD-95

Semaphorins are known to act as chemorepulsive molecules that guide axons during neural development. Sema4C, a group 4 semaphorin, is a transmembrane semaphorin of unknown function. The cytoplasmic domain of Sema4C contains a proline-rich region that may interact with some signaling proteins. In this study, we demonstrate that Sema4C is enriched in the adult mouse brain and associated with PSD-95 isoforms containing PDZ (PSD-95/DLG/ZO-1) domains, such as PSD-95/SAP90, PSD-93/chapsin110, and SAP97/DLG-1, which are concentrated in the post-synaptic density of the brain. In the neocortex, S4C is enriched in the synaptic vesicle fraction and Triton X-100 insoluble post-synaptic density fraction. Immunostaining for Sema4C overlaps that for PSD-95 in superficial layers I-IV of the neocortex. In neocortical culture, S4C is colocalized with PSD-95 in neurons, with a dot-like pattern along the neurites. Sema4C thus may function in the cortical neurons as a bi-directional transmembrane ligand through interacting with PSD-95.

Semaphorin 4C, a transmembrane semaphorin, [corrected] associates with a neurite-outgrowth-related protein, SFAP75

Semaphorin 4C (S4C, previously called M-SemaF) was recently identified as a brain rich transmembrane member of semaphorin family of the vertebrate. In the cytoplasmic domain of S4C there is a proline-rich region suggesting that the cytoplasmic domain may play an important role in Sema4C function. In this study, we have identified the cytoplasmic domain (cd) of M-SemaF(S4C)-associating protein with a Mr of 75 kDa, named SFAP75, from mouse brain. SFAP75 turned out to be the same as the recently reported neurite-outgrowth-related protein named Norbin. Deletion mutants analyses of S4C and SFAP75 revealed that the membrane-proximal region of S4Ccd binds to the intermediate region of SFAP75. Western blot and immunohistochemical analyses with anti-Sema4C and anti-SFAP75 antibodies indicated that S4C and SFAP75 were specially enriched in the brain with a similar distribution pattern to each other. These results suggest that S4C interacts with SFAP75 and plays a role in neural function in brain.

Mouse semaphorin H induces PC12 cell neurite outgrowth activating Ras-mitogen-activated protein kinase signaling pathway via Ca(2+) influx

We recently showed that mouse semaphorin H (MSH), a secreted semaphorin molecule, acts as a chemorepulsive factor on sensory neurites. In this study, we found for the first time that MSH induces neurite outgrowth in PC12 cells in a dose-dependent manner. Comparison of Ras-mitogen-activated protein kinase (MAPK) signaling pathways between MSH and nerve growth factor (NGF) revealed that these pathways are crucial for MSH action as well as NGF. K-252a, an inhibitor of tyrosine autophosphorylation of tyrosine kinase receptors (Trks), did not inhibit the action of MSH, suggesting that MSH action occurs via a different receptor than NGF. L- and N-types of voltage-dependent Ca(2+) channel blockers, diltiazem and omega-conotoxin, inhibited MSH-induced neurite outgrowth and MAPK phosphorylation in a Ca(2+)-dependent manner. A transient elevation in intracellular Ca(2+) level was observed upon MSH stimulation. These findings suggest that extracellular Ca(2+) influx, followed by activation of the Ras-MAPK signaling pathway, is required for MSH induced PC12 cell neurite outgrowth.

Characterization and expression of sema4g, a novel member of the semaphorin gene family

Semaphorins constitute a large and growing gene family, several members of which are axon guidance molecules. We report the characterization of sema4g, a novel class IV member of the semaphorin gene family, located on mouse chromosome 19. sema4g is expressed early in development in the brain, spinal cord, and several sensory organs as well as specific populations of projection neurons, compatible with the well-established function of semaphorins as axon guidance molecules.

Developmental localization of semaphorin H messenger RNA acting as a collapsing factor on sensory axons in the mouse brain

Semaphorins/collapsins, a family of genes with a semaphorin domain conserved from insects through to mammals, are believed to be involved in axon guidance during neuronal development. We report the expression patterns of mouse semaphorin messenger RNAs. Among secreted semaphorins, mouse semaphorin H is structurally most similar to semaphorin III/D, the first semaphorin identified as a collapsing factor for sensory axons. However, its expression patterns apparently differ from those of semaphorin III/D. The messenger RNAs are distributed in the brain widely but unevenly during development, in particular, in the main olfactory bulb, hippocampus and pontine nucleus. In the trunk, the expression level is high in mesodermal tissues surrounding the dorsal root ganglia, while it is low in the spinal cord. Moreover, we examined whether this molecule has activity to collapse growth cones of sensory neurons, as well as semaphorin III/D. Mouse semaphorin H collapsed growth cones of sensory neurons of the dorsal root ganglion in a dose-dependent manner, and anti-neuropilin antibodies inhibited this activity. Taken together, these results suggest that mouse semaphorin H can function as a chemorepellent to guide sensory peripheral nerves, most likely via neuropilin as a receptor.

Collapsin-1/semaphorin-III/D is regulated developmentally in Purkinje cells and collapses pontocerebellar mossy fiber neuronal growth cones

Most axons in the CNS innervate specific subregions or layers of their target regions and form contacts with specific types of target neurons, but the molecular basis of this process is not well understood. To determine whether collapsin-1/semaphorin-III/D, a molecule known to repel specific axons, might guide afferent axons within their cerebellar targets, we characterized its expression by in situ hybridization and observed its effects on mossy and climbing fiber extension and growth cone size in vitro. In newborn mice sema-D is expressed by cerebellar Purkinje cells in parasagittal bands located medially and in some cells of the cerebellar nuclei. Later, sema-D expression in Purkinje cells broadens such that banded expression is no longer prominent, and expression is detected in progressively more lateral regions. By postnatal day 16, expression is observed throughout the cerebellar mediolateral axis. Collapsin-1 protein, the chick ortholog of sema-D, did not inhibit the extension of neurites from explants of inferior olivary nuclei, the source of climbing fibers that innervate Purkinje cells. In contrast, when it was applied to axons extending from basilar pontine explants, a source of mossy fiber afferents of granule cells, collapsin-1 caused most pontine growth cones to collapse, as evidenced by a reduction in growth cone size of up to 59%. Moreover, 63% of pontine growth cones arrested their extension or retracted. Its effects on mossy fiber extension and its distribution suggest that sema-D prevents mossy fibers from innervating inappropriate cerebellar target regions and cell types.

A PDZ protein regulates the distribution of the transmembrane semaphorin, M-SemF

M-SemF is a membrane-associated, neurally enriched member of the semaphorin family of axon guidance signals. We considered whether the cytoplasmic domain of M-SemF might possess a signaling function and/or might control the distribution of M-SemF on the cell surface. We identify a PDZ-containing neural protein as an M-SemF cytoplasmic domain-associated protein (SEMCAP-1). SEMCAP-2 is a closely related nonneuronal protein. SEMCAP-1 has recently also been identified as GIPC, by virtue of its interaction with the RGS protein GAIP in vitro (De Vries, L., Lou, X., Zhao, G., Zheng, B., and Farquhar, M. G. (1998) Proc. Natl. Acad. Sci. U. S. A. 95, 12340-12345). Expression studies support the notion that SEMCAP-1(GIPC) interacts with M-SemF, but not GAIP, in brain. Lung SEMCAP-2 and SEMCAP-1(GIPC) are potential partners for both GAIP and M-SemF. The protein interaction requires the single PDZ domain of SEMCAP-1(GIPC) and the carboxyl-terminal four residues of M-SemF, ESSV. While SEMCAP-1(GIPC) also interacts with SemC, it does not interact with other proteins containing a class I PDZ binding motif, nor does M-SemF interact with other class I PDZ proteins. Co-expression of SEMCAP-1(GIPC) induces the redistribution of dispersed M-SemF into detergent-resistant aggregates in HEK293 cells. Thus, SEMCAP-1(GIPC) appears to regulate the subcellular distribution of M-SemF in brain, and SEMCAPs could link M-SemF to G protein signal transduction pathways.

Growth cone guidance: first steps towards a deeper understanding

Growth cones, the hand-like structures at the tip of growing neurites, possess remarkable abilities to detect directional cues. On their way to their targets they traverse a dense jungle of many different cells, expressing a variety of different molecular guidance cues. Proper reading and integration of these cues is essential for precise wiring of different parts of the peripheral and central nervous systems. Guidance cues have been classified according to the response they elicit as either attractive or repulsive. Recent work, however, suggests that this might not represent an absolute distinction and that the internal state of the growth cone can dictate whether it detects a cue as repulsive or attractive. This article reviews some new experimental approaches to understanding growth cone signal transduction mechanisms induced by extracellular guidance cues.

Mouse semaphorin H inhibits neurite outgrowth from sensory neurons

Mouse semaphorin H (M-semaH) was structurally similar to semaphorin III/D, a mammalian homologue of collapsin 1 which was identified as a collapsing factor for sensory nerves. In this study we investigated the expression patterns of M-semaH mRNA and the protein binding sites in the trunk of mouse embryos. M-semaH mRNA was expressed in the mesenchymal tissues surrounding each dorsal root ganglia. These tissues include the caudal sclerotome and perinotochordal mesenchyme, which were thought to express factors repulsive to axons. M-semaH binding was detected on the spinal nerves. We further investigated, using in vitro co-culture assay, whether M-semaH acted as a chemorepulsive molecule on sensory axons. The results suggested that M-semaH was a candidate for a chemorepellent expressed in the mesenchyme surrounding the sensory ganglia, which is involved in the axonal guidance mechanism of sensory nerves in the trunk.

Cloning, expression, and genetic mapping of Sema W, a member of the semaphorin family

The semaphorins comprise a large family of membrane-bound and secreted proteins, some of which have been shown to function in axon guidance. We have cloned a transmembrane semaphorin, Sema W, that belongs to the class IV subgroup of the semaphorin family. The mouse and rat forms of Sema W show 97% amino acid sequence identity with each other, and each shows about 91% identity with the human form. The gene for Sema W is divided into 15 exons, up to 4 of which are absent in the human cDNAs that we sequenced. Unlike many other semaphorins, Sema W is expressed at low levels in the developing embryo but was found to be expressed at high levels in the adult central nervous system and lung. Functional studies with purified membrane fractions from COS7 cells transfected with a Sema W expression plasmid showed that Sema W has growth-cone collapse activity against retinal ganglion-cell axons, indicating that vertebrate transmembrane semaphorins, like secreted semaphorins, can collapse growth cones. Genetic mapping of human SEMAW with human/hamster radiation hybrids localized the gene to chromosome 2p13. Genetic mapping of mouse Semaw with mouse/hamster radiation hybrids localized the gene to chromosome 6, and physical mapping placed the gene on bacteria artificial chromosomes carrying microsatellite markers D6Mit70 and D6Mit189. This localization places Semaw within the locus for motor neuron degeneration 2, making it an attractive candidate gene for this disease.

Expression of mouse semaphorin H mRNA in the inner ear of mouse fetuses

Semaphorins constitute a large family of secreted and cell-surfaced proteins that appear to function as chemorepellents to guide axons. We examined the expression pattern of M-semaH mRNA in the inner ear of mouse fetuses by in situ hybridization histochemistry. M-semaH mRNA expression was high in the endolymphatic sac involved in endolymph homeostasis. It was also high in the semicircular ducts except for the crista ampullaris, whereas no expression was detected in the epithelium of cochlear ducts.

Cloning and characterization of a novel class VI semaphorin, semaphorin Y

Semaphorins comprise a large family of proteins implicated in axonal guidance. We cloned a novel transmembrane semaphorin, semaphorin Y (Sema Y), which has a class VI sema domain. Sema Y shows growth cone collapsing activity on DRG neurons in vitro, and the target regions of the DRG neurons express sema Y mRNA during development. Sema Y may be a stop signal for these neurons in their target areas. Interestingly, sema Y mRNA was also detected in other neurons and their targets. Two isoforms of Sema Y derived from alternative splicing were identified and their expression was found to be regulated in a tissue- and age-dependent manner. Distribution of sema Y mRNA suggests that Sema Y might also be important during maintenance of axonal connections and/or differentiation and migration of cells. Sequence comparison among class VI semaphorins revealed two short conserved sequence stretches in their cytoplasmic domains, suggesting interaction of these semaphorins with a common intracellular component(s).

Analysis of a Zebrafish semaphorin reveals potential functions in vivo

The semaphorin/collapsin gene family is a large and diverse family encoding both secreted and transmembrane proteins, some of which are thought to act as repulsive axon guidance molecules. However, the function of most semaphorins is still unknown. We have cloned and characterized several semaphorins in the zebrafish in order to assess their in vivo function. Zebrafish semaZ2 is expressed in a dynamic and restricted pattern during the period of axon outgrowth that indicates potential roles in the guidance of several axon pathways. Analysis of mutant zebrafish with reduced semaZ2 expression reveals axon pathfinding errors that implicate SemaZ2 in normal guidance.

Cloning and expression pattern of a murine semaphorin homologous to H-sema IV

The semaphorin/collapsin family of proteins comprises molecules thought to be important for the guidance of growing axons. All members of this family, which includes both secreted and cell-surface molecules, share a conserved domain of approximately 500 amino acids. Here, we report the cloning of a novel murine semaphorin, termed M-sema IV. It displays 96.3% identity to the human semaphorin H-sema IV and is therefore likely to be the respective murine homologue. In addition, an isoform was identified, which contains an additional 31 amino acids in the semaphorin domain. M-sema IV appears to be expressed ubiquitously in adulthood. During embryogenesis, in situ hybridization revealed M-sema IV expression in subregions of the central nervous system and various other tissues like skin, kidney, lung and intestine.

Expression of copper trafficking genes in the mouse brain

Copper homeostasis in the brain must be strictly maintained, since copper is an essential trace element and is potentially toxic. To understand the mechanism of copper homeostasis in the brain, we cloned several mouse homologues of copper trafficking genes and performed in situ hybridization histochemistry. mCTR1, mATX1, and mATP7a were highly expressed in the choroid plexus, indicating that the choroid plexus uses the trafficking pathway from uptake to efflux to transport copper to the cerebrospinal fluids. We suggest that these genes may regulate copper concentration in the brain through the choroid plexus.

Semaphorins A and E act as antagonists of neuropilin-1 and agonists of neuropilin-2 receptors

Neuropilin-1 (NP-1) has been identified as a necessary component of a semaphorin D (SemD) receptor that repulses dorsal root ganglion (DRG) axons during development. SemA and SemE are related to SemD and bind to NP-1, but do not repulse DRG axons. By expressing NP-1 in retinal neurons and NP-2 in DRG neurons, we demonstrate that neuropilins are sufficient to determine the functional specificity of semaphorin responsiveness. SemA and SemE block SemD binding to NP-1 and abolish SemD repulsion in axons expressing NP-1. SemA and SemE seem to have a newly discovered protein antagonist capacity at NP-1 receptors, whereas they act as agonists at receptors containing NP-2.

New eukaryotic semaphorins with close homology to semaphorins of DNA viruses

Semaphorins were initially described as a family of repulsive guidance molecules in embryonal development. Their basic structure consists of an N-terminal signal sequence, the defining semaphorin domain ofapproximately 500 amino acids, an Ig-like domain,and a variable carboxy-terminus. We recently described a viral semaphorin homologue encoded by the alcelaphine herpesvirus type 1. Less conserved, truncated homologues were also identified in poxviruses. Here we describe new human and murine semaphorin homologues. The respective genes were cloned and sequenced, and they were termed H-Sema-L and M-Sema-L (HGMW-approved symbols SEMAL and Semal, respectively). A multiply spliced mRNA of 3.2 kb is expressed in human placenta, spleen, thymus, and gonadal tissue. H-Sema-L maps to chromosome 15q22.3-q23 and M-Sema-L to the homologous locus 9A3.3-B in the mouse genome. The expression patterns and the presence of related genes in large DNA viruses suggest that this new semaphorin has a relevant function in the immune system.

Many major CNS axon projections develop normally in the absence of semaphorin III

The semaphorins constitute a large gene family of transmembrane and secreted molecules, many of which are expressed in the nervous system. Genetic studies in Drosophila have revealed a role for semaphorins in axon guidance and synapse formation, and several in vitro studies in mice have demonstrated a dramatic chemorepellent effect of semaphorin III (Sema III) on the axons of several populations of neurons. To investigate the function of Sema III during in vivo axon guidance in the mammalian CNS, we studied the development of axonal projections in mutant mice lacking Sema III. Projections were studied for which either the in vitro evidence suggests a role for Sema III in axon guidance (e.g., cerebellar mossy fibers, thalamocortical axons, or cranial motor neurons) or the in vivo expression suggests a role for Sema III in axon guidance (e.g., cerebellar Purkinje cells, neocortex). We find that many major axonal projections, including climbing fiber, mossy fiber, thalamocortical, and basal forebrain projections and cranial nerves, develop normally in the absence of Sema III. Despite its in vitro function and in vivo expression, it appears as if Sema III is not absolutely required for the formation of many major CNS tracts. Such data are consistent with recent models suggesting that axon guidance is controlled by a balance of forces resulting from multiple guidance cues. Our data lead us to suggest that if Sema III functions in part to guide the formation of major axonal projections, then it does so in combination with both other semaphorins and other families of guidance molecules.

The chemorepulsive activity of the axonal guidance signal semaphorin D requires dimerization

The axonal guidance signal semaphorin D is a member of a large family of proteins characterized by the presence of a highly conserved semaphorin domain of about 500 amino acids. The vertebrate semaphorins can be divided into four different classes that contain both secreted and membrane-bound proteins. Here we show that class III (SemD) and class IV semaphorins (SemB) form homodimers linked by intermolecular disulfide bridges. In addition to the 95-kDa form of SemD (SemD(95k)), proteolytic processing of SemD creates a 65-kDa isoform (SemD(65k)) that lacks the 33-kDa carboxyl-terminal domain. Although SemD(95k) formed dimers, the removal of the carboxyl-terminal domain resulted in the dissociation of SemD homodimers to monomeric SemD(65k). Mutation of cysteine 723, one of four conserved cysteine residues in the 33-kDa fragment, revealed its requirement both for the dimerization of SemD and its chemorepulsive activity. We suggest that dimerization is a general feature of sema- phorins which depends on class-specific sequences and is important for their function.

Neuronal and non-neuronal collapsin-1 binding sites in developing chick are distinct from other semaphorin binding sites

The collapsin and semaphorin family of extracellular proteins contributes to axonal path finding by repulsing axons and collapsing growth cones. To explore the mechanism of collapsin-1 action, we expressed and purified a truncated collapsin-1-alkaline phosphatase fusion protein (CAP-4). This protein retains biological activity as a DRG growth cone collapsing agent and saturably binds to DRG neurons with low nanomolar affinity. Specific CAP-4 binding sites are present on DRG neurons, sympathetic neurons, and motoneurons, but not on retinal, cortical, or brainstem neurons. Outside the nervous system, high levels of CAP-4 binding sites are present in the mesenchyme surrounding major blood vessels and developing bone and in lung. These sites provide a substrate for the collapsin-1-dependent patterning of non-neuronal tissues perturbed in sema III (-/-) mice. The staining patterns for mouse semaphorin D/III and chick collapsin-1 fusion proteins are indistinguishable from one another but quite separate from that for semaphorin B and M-semaphorin F fusion proteins. These data imply that a family of high-affinity semaphorin binding sites similar in complexity to the semaphorin ligand family exists.

A novel transmembrane semaphorin can bind c-src

The semaphorins/collapsins constitute a family of genes unified by the presence of a "semaphorin domain" which has been conserved through metazoan evolution. The semaphorin family comprises both secreted and transmembrane molecules and is thought to be made up of ligands for as yet unidentified receptors. The functions are not known, with the exception of those of sema III (also referred as sem D and collapsin 1), D-sema I, and D-sema II, which have been shown to be involved in axonal pathfinding. Here report the identification of a mouse semaphorin cDNA, termed Sema VIb. Although Sema VIb contains the extracellular semaphorin domain, it lacks the immunoglobulin domain or thrombospondin repeats which are present in other described vertebrate (but not invertebrate) transmembrane semaphorins. During development Sema VIb mRNA is expressed in subregions of the nervous system and is particularly prominent in muscle. In adulthood, Sema VIb mRNA is expressed ubiquitously. The cytoplasmic domain of Sema VIb contains several proline-rich potential SH3 domain binding sites. Using an in vitro binding assay, we show that Sema VIb binds specifically the SH3 domain of the protooncogene c-src. In transfected COS cells Sema VIb coimmunoprecipitates with c-src. These results, along with our evidence that Sema VIb can form dimers, suggests that the semaphorin family not only serves as ligands but may include members, especially those which are transmembrane, which serve as receptors, triggering intracellular signaling via an src-related cascade.

Molecular cloning of a novel member of semaphorin family genes, semaphorin Z

Semaphorins/collapsins (semaphorins) comprise a large family of proteins implicated in axonal guidance during development. We cloned a novel member (semaZ) of the semaphorin gene family from a rat brain cDNA library. Sema Z was thought to be an integral membrane glycoprotein of 887 amino acids including a sema domain composed of 532 amino acids. The amino acid sequence of Sema Z showed 28-35% identity with other semaphorins in its sema domain, including 15 conserved cysteine residues. The cytoplasmic domain of Sema Z was found to be rich in prolines. Our phylogenetic analysis based on the amino acid sequence of the sema domains and the location of conserved N-glycosylation sites suggested that the sema domain of Sema Z belongs to a new class, class VI. We detected the semaZ mRNA in the first branchial arch of embryonic day 11 (E11) rat embryo, and subsequently in the myotomes and the dorsal root ganglia in developing somites from E11.5 through E13.5, but not in the brain. However, at E15, 18, 21 and P0, semaZ was highly expressed in the brain. Sema Z might play a role in both peripheral and central nervous system development.

The human semaphorin-like leukocyte cell surface molecule CD100 associates with a serine kinase activity

CD100 is a 150-kDa homodimeric glycoprotein broadly expressed on the surface of human hematopoietic cells. CD100 has been recently identified as the first lymphoid gene that belongs to the semaphorin gene family. Semaphorins function as chemorepellent molecules in the nervous system, but the function of CD100 remains poorly understood. In lymphoid cells, it has been suggested to play a role in homotypic cell adhesion and in T cell activation. We demonstrate that in T cells and natural killer cells a serine kinase activity is immunoprecipitated with CD100. Distinct epitopes of CD100 have been defined with specific monoclonal antibodies, mediating opposite effects at the functional level, especially in T cells. The kinase activity is retained only with an antibody against a particular epitope of CD100. Additionally, a fusion protein containing the cytoplasmic domain of the molecule retains the kinase activity in cellular lysates, and CD100 itself is presumably a favorite substrate of the kinase. These findings suggest that a serine kinase pathway may participate in the different functional effects triggered through the distinct epitopes of CD100 and is likely involved in the biological effects of this semaphorin-like leukocyte cell surface molecule.

Disruption of semaphorin III/D gene causes severe abnormality in peripheral nerve projection

The molecules of the collapsin/semaphorin gene family have been thought to play an essential role in axon guidance during development. Semaphorin III/D is a member of this family, has been shown to repel dorsal root ganglion (DRG) axons in vitro, and has been implicated in the patterning of sensory afferents in the spinal cord. Although semaphorin III/D mRNA is expressed in a wide variety of neural and nonneural tissues in vivo, the role played by semaphorin III/D in regions other than the spinal cord is not known. Here, we show that mice homozygous for a targeted mutation in semaphorin III/D show severe abnormality in peripheral nerve projection. This abnormality is seen in the trigeminal, facial, vagus, accessory, and glossopharyngeal nerves but not in the oculomotor nerve. These results suggest that semaphorin III/D functions as a selective repellent in vivo.

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

Semaphorins are a large family of secreted and transmembrane proteins, several of which are implicated in repulsive axon guidance. Neuropilin (neuropilin-1) was recently identified as a receptor for Collapsin-1/Semaphorin III/D (Sema III). We report the identification of a related protein, neuropilin-2, whose mRNA is expressed by developing neurons in a pattern largely, though not completely, nonoverlapping with that of neuropilin-1. Unlike neuropilin-1, which binds with high affinity to the three structurally related semaphorins Sema III, Sema E, and Sema IV, neuropilin-2 shows high affinity binding only to Sema E and Sema IV, not Sema III. These results identify neuropilins as a family of receptors (or components of receptors) for at least one semaphorin subfamily. They also suggest that the specificity of action of different members of this subfamily may be determined by the complement of neuropilins expressed by responsive cells.

Rac1 mediates collapsin-1-induced growth cone collapse

Collapsin-1 or semaphorin III(D) inhibits axonal outgrowth by collapsing the lamellipodial and filopodial structures of the neuronal growth cones. Because growth cone collapse is associated with actin depolymerization, we considered whether small GTP-binding proteins of the rho subfamily might participate in collapsin-1 signal transduction. Recombinant rho, rac1, and cdc42 proteins were triturated into embryonic chick (DRG) neurons. Constitutively active rac1 increases the proportion of collapsed growth cones, and dominant negative rac1 inhibits collapsin-1-induced collapse of growth cones and collapsin-1 inhibition of neurite outgrowth. DRG neurons treated with dominant negative rac1 remain sensitive to myelin-induced growth cone collapse. Similar mutants of cdc42 do not alter growth cone structure, neurite elongation, or collapsin-1 sensitivity. Whereas the addition of activated rho has no effect, the inhibition of rho with Clostridium botulinum C3 transferase stimulates the outgrowth of DRG neurites. C3 transferase-treated growth cones exhibit little or no lamellipodial spreading and are minimally responsive to collapsin-1 and myelin. These data demonstrate a prominent role for rho and rac1 in modulating growth cone motility and indicate that rac1 may mediate collapsin-1 action.

Cloning and expression of a novel murine semaphorin with structural similarity to insect semaphorin I

We describe a novel semaphorin family member, Sema VIa, with 25-36% sequence identity at the amino acid level in the semaphorin domain to previously published mouse homologues. This novel family member shares considerable homology with the best characterized murine semaphorin, Sema III (also known as SemD), at the 5' end but is divergent from Sema III near the 3' end because it contains a putative transmembrane domain. Remarkably, of the known semaphorins, Sema VIa bears the greatest structural similarity to insect Sema I, although it contains a much larger intracellular domain. We propose, therefore, that Sema VIa is the prototype of a new class (class VI) of semaphorins. In order to gain insights into potential functions of Sema VIa, we have compared mRNA expression of Sema VIa to that of Sema III during development. In the nervous system, Sema VIa is expressed in strikingly localized and transient patterns that are markedly different from those of Sema III. Interestingly, Sema VIa and Sema III frequently exhibit complementary or adjacent loci of expression. We suggest that Sema VIa may be important to nervous system development via a mechanism that involves cell-cell communication.

Identification of a novel transmembrane semaphorin expressed on lymphocytes

Semaphorin (also known as collapsin) members are thought to be involved in axon guidance during neural network formation. Here, we report the isolation of a novel member, mouse semaphorin G (M-sema G), which encodes a semaphorin domain followed by a single putative immunoglobulin-like domain, a transmembrane domain, and a cytoplasmic domain. M-sema G is most closely related to M-sema F, which we previously reported, and semB and semC. These four members appear to constitute a transmembrane type subfamily in mouse semaphorins. In contrast to the predominant expression of M-sema F mRNAs in the nervous tissues, M-sema G mRNAs are strongly expressed in lymphoid tissues, especially in the thymus, as well as in the nervous tissues. The mRNAs are also detected in various cell lines from hematopoietic cells. By generating specific antibodies, we confirmed the strong expression of M-Sema G proteins on the surface of lymphocytes. These results provide the first evidence that semaphorin is expressed on lymphocytes and suggest that semaphorins may play an important role in the immune system, as well as in the nervous system.

Anatomy of rat semaphorin III/collapsin-1 mRNA expression and relationship to developing nerve tracts during neuroembryogenesis

Semaphorin III/collapsin-1 (semaIII/coll-1) is a chemorepellent that exhibits a repulsive effect on growth cones of dorsal root ganglion neurons. To identify structures that express semaIII/coll-1 in developing mammals, we cloned the rat homologue and performed in situ hybridization on embryonic, neonatal, and adult rats. The relationship between semaIII/coll-1 mRNA distribution and developing nerve tracts was studied by combining in situ hybridization with immunohistochemistry for markers of growing nerve fibers. At embryonic day 11, semaIII/coll-1 expression was restricted to the olfactory pit, the basal and rostral surface of the telencephalic vesicle, the anlage of the eye, the epithelium of Rathke's pouch, and the somites. At later developmental stages, semaIII/coll-1 mRNA was found to be widely distributed in neuronal as well as in mesenchymal and epithelial structures outside the nervous system. Strong expression was found in the olfactory bulb, retina, lens, piriform cortex, amygdalostriatal area, pons, cerebellar anlage, motor nuclei of cranial nerves, and ventral spinal cord. After birth, mesenchymal staining decreased rapidly and expression became progressively restricted to specific sets of neurons in the central nervous system (CNS). In the mature CNS, semaIII/coll-1 mRNA remains detectable in mitral cells, neurons of the accessory bulb and cerebral cortex, cerebellar Purkinje cells, as well as a subset of cranial and spinal motoneurons. The temporal and spatial expression pattern of semaIII/coll-1 mRNA and its relationship to emerging nerve tracts suggests that semaIII/coll-1 is involved in guiding growing axons towards their targets by forming a molecular boundary that instructs axons to engage in the formation of specific nerve tracts.