Semaphorin 3A: A new player in bone remodeling

Semaphorin 3A (Sema3A) is a protein identified originally as a diffusible axonal chemorepellent. Sema3A has multifunctional roles in embryonic development, immune regulation, vascularization, and oncogenesis. Bone remodeling consists of two phases: the removal of mineralized bone by osteoclasts and the formation of new bone by osteoblasts, and plays an essential role in skeletal diseases such as osteoporosis. Recent studies have shown that Sema3A is implicated in the regulation of osteoblastgenesis and osteoclastgenesis. Moreover, low bone mass in mice with specific knockout of Sema3A in the neurons indicates that Sema3A regulates bone remodeling indirectly. This review highlights recent advances on our understanding of the role of sema3A as a new player in the regulation of bone remodeling and proposes the potential of sema3A in the diagnosis and therapy of bone diseases.     

Sema3a1 guides spinal motor axons in a cell- and stage-specific manner in zebrafish

In order for axons to reach their proper targets, both spatiotemporal regulation of guidance molecules and stepwise control of growth cone sensitivity to guidance molecules is required. Here, we show that, in zebrafish, Sema3a1, a secreted class 3 semaphorin, plays an essential role in guiding the caudal primary (CaP) motor axon that pioneers the initial region of the motor pathway. The expression pattern of Sema3a1 suggests that it delimits the pioneer CaP axons to the initial, common pathway via a repulsive action, but then CaP axons become insensitive to Sema3a1 beyond the common pathway. Indeed, nrp1a, which probably encodes a component of the Sema3a1 receptor, is specifically expressed by CaP during the early part of its outgrowth but not during later stages when extending into sema3a1-expressing muscle cells. To examine this hypothesis directly, expression of sema3a1 and/or nrp1a was manipulated in several ways. First, antisense knockdown of Sema3a1 induced CaP axons to branch excessively, stall and/or follow aberrant pathways. Furthermore, dynamic analysis showed they extended more lateral filopodia and often failed to pause at the horizontal myoseptal choice point. Second, antisense knockdown of Nrp1a and double knockdown of Nrp1a/Sema3a1 induced similar outgrowth defects in CaP. Third, CaP axons were inhibited by focally misexpressed sema3a1 along the initial common pathway but not along their pathway beyond the common pathway. Thus, as predicted, Sema3a1 is repulsive to CaP axons in the common region of the pathway, but not beyond the common pathway. Fourth, induced ubiquitous overexpression of sema3a1 caused the CaP axons but not the other primary motor axons to follow aberrant pathways. These results suggest that the repulsive response to Sema3a1 of the primary motor axons along the common pathway is both cell-type specific and dynamically regulated, perhaps via regulation of nrp1a.     

Plexina1 autoinhibition by the plexin sema domain

Semaphorin 3A (Sema3A) binds to neuropilin-1 (NP1) and activates the transmembrane Plexin to transduce a repulsive axon guidance signal. Here, we show that Sema3 signals are transduced equally effectively by PlexinA1 or PlexinA2, but not by PlexinA3. Deletion analysis of the PlexinA1 ectodomain demonstrates that the sema domain prevents PlexinA1 activation in the basal state. Sema-deleted PlexinA1 is constitutively active, producing cell contraction, growth cone collapse, and inhibition of neurite outgrowth. The sema domain of PlexinA1 physically associates with the remainder of the PlexinA1 ectodomain and can reverse constitutive activation. Both the sema portion and the remainder of the ectodomain of PlexinA1 associate with NP1 in a Sema3A-independent fashion. Plexin A1 is autoinhibited by its sema domain, and Sema3A/NP1 releases this inhibition.     

Cationic Peptides and Peptidomimetics Bind Glycosaminoglycans as Potential Sema3A Pathway Inhibitors

Semaphorin3A (Sema3A) is a vertebrate-secreted protein that was initially characterized as a repulsive-guidance cue. Semaphorins have crucial roles in several diseases; therefore, the development of Sema3A inhibitors is of therapeutic interest. Sema3A interacts with glycosaminoglycans (GAGs), presumably through its C-terminal basic region. We used different biophysical techniques (i.e., NMR, surface plasmon resonance, isothermal titration calorimetry, fluorescence, and UV-visible spectroscopy) to characterize the binding of two Sema3A C-terminus-derived basic peptides (FS2 and NFS3) to heparin and chondroitin sulfate A. We found that these peptides bind to both GAGs with affinities in the low-micromolar range. On the other hand, a peptoid named SICHI (semaphorin-induced chemorepulsion inhibitor), which is positively charged at physiological pH, was first identified by our group as being able to block Sema3A chemorepulsion and growth-cone collapse in axons at the extracellular level. To elucidate the direct target for the reported SICHI inhibitory effect in the Sema3A signaling pathway, we looked first to the protein-protein interaction between secreted Sema3A and the Nrp1 receptor. However, our results show that SICHI does not bind directly to the Sema3A sema domain or to Nrp1 extracellular domains. We evaluated a new, to our knowledge, hypothesis, according to which SICHI binds to GAGs, thereby perturbing the Sema3A-GAG interaction. By using the above-mentioned techniques, we observed that SICHI binds to GAGs and competes with Sema3A C-terminus-derived basic peptides for binding to GAGs. These data support the ability of SICHI to block the biologically relevant interaction between Sema3A and GAGs, thus revealing SICHI as a new, to our knowledge, class of inhibitors that target the GAG-protein interaction.     

Semaphorin-3D and Semaphorin-3E Inhibit the Development of Tumors from Glioblastoma Cells Implanted in the Cortex of the Brain

Class-3 semaphorins are secreted axon guidance factors. Some of these semaphorins have recently been characterized as suppressors of tumor progression. To determine if class-3 semaphorins can be used to inhibit the development of glioblastoma-multiforme tumors, we expressed recombinant sema-3A, 3B, 3D, 3E, 3F or 3G in U87MG glioblastoma cells. Sema3A and sema3B expressing cells contracted and changed shape persistently while cells expressing other semaphorins did not. Sema3A and sema3F differed from other semaphorins including sema3B as they also inhibited the proliferation of the cells and the formation of soft agar colonies. With the exception of sema3G and sema3B, expression of these semaphorins in U87MG cells inhibited significantly tumor development from subcutaneously implanted cells. Strong inhibition of tumor development was also observed following implantation of U87MG cells expressing each of the class-3 semaphorins in the cortex of mouse brains. Sema3D and sema3E displayed the strongest inhibitory effects and their expression in U373MG or in U87MG glioblastoma cells implanted in the brains of mice prolonged the survival of the mice by more then two folds. Furthermore, most of the mice that died prior to the end of the experiment did not develop detectable tumors and many of the mice survived to the end of the experiment. Most of the semaphorins that we have used here with the exception of sema3D were characterized previously as inhibitors of angiogenesis. Our results indicate that sema3D also functions as an inhibitor of angiogenesis and suggest that the anti-tumorigenic effects are due primarily to inhibition of tumor angiogenesis. These results indicate that class-3 semaphorins such as sema3D and sema3E could perhaps be used to treat glioblastoma patients.     

Semaphorin 2a secreted by oenocytes signals through plexin B and plexin A to guide sensory axons in the Drosophila embryo

The semaphorin gene family has been shown to play important roles in axonal guidance in both vertebrates and invertebrates. Both transmembrane (Sema1a, Sema1b, Sema5c) and secreted (Sema2a, Sema2b) forms of semaphorins exist in Drosophila. Two Sema receptors, plexins (Plex) A and B, have also been identified. Many questions remain concerning the axon guidance functions of the secreted semaphorins, including the identity of their receptors. We have used the well-characterized sensory system of the Drosophila embryo to address these problems. We find novel sensory axon defects in sema2a loss-of-function mutants in which particular axons misproject and follow inappropriate pathways to the CNS. plexB loss-of-function mutants show similar phenotypes to sema2a mutants and sema2a interacts genetically with plexB, supporting the hypothesis that Sema2a signals through PlexB receptors. Sema2a protein is expressed by larval oenocytes, a cluster of secretory cells in the lateral region of the embryo and the sema2a mutant phenotype can be rescued by driving Sema2a in these cells. Ablation of oenocytes results in sensory axon defects similar to the sema2a mutant phenotype. These data support a model in which Sema2a, while being secreted from oenocytes, acts in a highly localized fashion: It represses axon extension from the sensory neuron cell body, but only in regions in direct contact with oenocytes.     

Semaphorin3a1 regulates angioblast migration and vascular development in zebrafish embryos

Semaphorins are a large family of secreted and cell surface molecules that guide neural growth cones to their targets during development. Some semaphorins are expressed in cells and tissues beyond the nervous system suggesting the possibility that they function in the development of non-neural tissues as well. In the trunk of zebrafish embryos endothelial precursors (angioblasts) are located ventral and lateral to the somites. The angioblasts migrate medially and dorsally along the medial surface of the somites to form the dorsal aorta just ventral to the notochord. Here we show that in zebrafish Sema3a1 is involved in angioblast migration in vivo. Expression of sema3a1 in somites and neuropilin 1, which encodes for a component of the Sema3a receptor, in angioblasts suggested that Sema3a1 regulates the pathway of the dorsally migrating angioblasts. Antisense knockdown of Sema3a1 inhibited the formation of the dorsal aorta. Induced ubiquitous expression of sema3a1 in hsp70:(gfp)sema3a1(myc) transgenic embryos inhibited migration of angioblasts ventral and lateral to the somites and retarded development of the dorsal aorta, resulting in severely reduced blood circulation. Furthermore, analysis of cells that express angioblast markers following induced expression of sema3a1 or in a mutant that changes the expression of sema3a1 in the somites confirmed these results. These data implicate Sema3a1, a guidance factor for neural growth cones, in the development of the vascular system.     

Semaphorin 5A is a bifunctional axon guidance cue for axial motoneurons in vivo

Semaphorins are a large class of proteins that function throughout the nervous system to guide axons. It had previously been shown that Semaphorin 5A (Sema5A) was a bifunctional axon guidance cue for mammalian midbrain neurons. We found that zebrafish sema5A was expressed in myotomes during the period of motor axon outgrowth. To determine whether Sema5A functioned in motor axon guidance, we knocked down Sema5A, which resulted in two phenotypes: a delay in motor axon extension into the ventral myotome and aberrant branching of these motor axons. Both phenotypes were rescued by injection of full-length rat Sema5A mRNA. However, adding back RNA encoding the sema domain alone significantly rescued the branching phenotype in sema5A morphants. Conversely, adding back RNA encoding the thrombospondin repeat (TSR) domain alone into sema5A morphants exclusively rescued delay in ventral motor axon extension. Together, these data show that Sema5A is a bifunctional axon guidance cue for vertebrate motor axons in vivo. The TSR domain promotes growth of developing motor axons into the ventral myotome whereas the sema domain mediates repulsion and keeps these motor axons from branching into surrounding myotome regions.     

Semaphorin signaling guides cranial neural crest cell migration in zebrafish

Cranial neural crest cells (NCCs) migrate into the pharyngeal arches in three primary streams separated by two cranial neural crest (NC)-free zones. Multiple tissues have been implicated in the guidance of cranial NCC migration; however, the signals provided by these tissues have remained elusive. We investigate the function of semaphorins (semas) and their receptors, neuropilins (nrps), in cranial NCC migration in zebrafish. We find that genes of the sema3F and sema3G class are expressed in the cranial NC-free zones, while nrp2a and nrp2b are expressed in the migrating NCCs. sema3F/3G expression is expanded homogeneously in the head periphery through which the cranial NCCs migrate in lzr/pbx4 mutants, in which the cranial NC streams are fused. Antisense morpholino knockdown of Sema3F/3G or Nrp2 suppresses the abnormal cranial NC phenotype of lzr/pbx4 mutants, demonstrating that aberrant Sema3F/3G-Nrp2 signaling is responsible for this phenotype and suggesting that repulsive Sema3F/3G-Npn2 signaling normally contributes to the guidance of migrating cranial NCCs. Furthermore, global over-expression of sema3Gb phenocopies the aberrant cranial NC phenotype of lzr/pbx4 mutants when endogenous Sema3 ligands are knocked down, consistent with a model in which the patterned expression of Sema3 ligands in the head periphery coordinates the migration of Nrp-expressing cranial NCCs.     

Semaphorin 3d promotes cell proliferation and neural crest cell development downstream of TCF in the zebrafish hindbrain

Neural crest cells (NCCs) are pluripotent migratory cells that are crucial to the development of the peripheral nervous system, pigment cells and craniofacial cartilage and bone. NCCs are specified within the dorsal ectoderm and undergo an epithelial to mesenchymal transition (EMT) in order to migrate to target destinations where they differentiate. Here we report a role for a member of the semaphorin family of cell guidance molecules in NCC development. Morpholino-mediated knockdown of Sema3d inhibits the proliferation of hindbrain neuroepithelial cells. In addition, Sema3d knockdown reduces markers of migratory NCCs and disrupts NCC-derived tissues. Similarly, expression of a dominant-repressor form of TCF (DeltaTCF) reduces hindbrain cell proliferation and leads to a disruption of migratory NCC markers. Moreover, expression of DeltaTCF downregulates sema3d RNA expression. Finally, Sema3d overexpression rescues reduced proliferation caused by DeltaTCF expression, suggesting that Sema3d lies downstream of Wnt/TCF signaling in the molecular pathway thought to control cell cycle in NCC precursors.     

Fyn and Cdk5 mediate semaphorin-3A signaling,which is involved in regulation of dendrite orientation in cerebral cortex

Semaphorin-3A (Sema3A), a member of class 3 semaphorins, regulates axon and dendrite guidance in the nervous system. How Sema3A and its receptors plexin-As and neuropilins regulate neuronal guidance is unknown. We observed that in fyn- and cdk5-deficient mice, Sema3A-induced growth cone collapse responses were attenuated compared to their heterologous controls. Cdk5 is associated with plexin-A2 through the active state of Fyn. Sema3A promotes Cdk5 activity through phosphorylation of Tyr15, a phosphorylation site with Fyn. A Cdk5 mutant (Tyr15 to Ala) shows a dominant-negative effect on the Sema3A-induced collapse response. The sema3A gene shows strong interaction with fyn for apical dendrite guidance in the cerebral cortex. We propose a signal transduction pathway in which Fyn and Cdk5 mediate neuronal guidance regulated by Sema3A.     

Semaphorin-1a is required for Aedes aegypti embryonic nerve cord development

Although mosquito genome projects have uncovered orthologues of many known developmental regulatory genes, extremely little is known about mosquito development. In this study, the role of semaphorin-1a (sema1a) was investigated during vector mosquito embryonic ventral nerve cord development. Expression of sema1a and the plexin A (plexA) receptor are detected in the embryonic ventral nerve cords of Aedes aegypti (dengue vector) and Anopheles gambiae (malaria vector), suggesting that Sema1a signaling may regulate mosquito nervous system development. Analysis of sema1a function was investigated through siRNA-mediated knockdown in A. aegypti embryos. Knockdown of sema1a during A. aegypti development results in a number of nerve cord phenotypes, including thinning, breakage, and occasional fusion of the longitudinal connectives, thin or absent commissures, and general distortion of the nerve cord. Although analysis of Drosophila melanogaster sema1a loss-of-function mutants uncovered many similar phenotypes, aspects of the longitudinal phenotypes differed between D. melanogaster and A. aegypti. The results of this investigation suggest that Sema1a is required for development of the insect ventral nerve cord, but that the developmental roles of this guidance molecule have diverged in dipteran insects.     

The Involvement of Immune Semaphorins in the Pathogenesis of Inflammatory Bowel Diseases (IBDs)

ResultsThe percentage (%) of T regulatory cells (Tregs) expressing sema3A in patients with active CD (64.5% ±14.49%) and active UC (49.8% ±16.45%) was significantly lower when compared to that of healthy controls (88.7% ±3.6%, p< 0.001 and p< 0.0001, respectively). This expression was seen to be in negative correlation with CD activity. Serum levels of Sema4A were significantly lower in patients with CD and UC when compared to that of controls (5.69±1.48ng\ml for CD, 5.26±1.23 ng/ml for UC patients vs 9.74±2.73ng/ml for normal controls, P<0.001). Sema4A was highly expressed in lymphocytes of the lamina propria of CD and UC patients but absent in patients with diverticulitis or in normal individuals.ConclusionsAltered % of Tregs expressing sema3A in patients with inflammatory bowel diseases (IBD) is partially responsible for their failure in preventing CD4+ effector T cell induced inflammation in IBD in peripheral blood. The increased expression of sema4A in bowel biopsies from CD and UC patients is suggestive of its central role in regulating local tissue inflammation in the bowel.     

Semaphorin 3A is a marker for disease activity and a potential immunoregulator in systemic lupus erythematosus

Introduction

Semaphorin 3A (sema3A) and neuropilin-1 (NP-1) play a regulatory role in immune responses and have a demonstrated effect on the course of collagen induced arthritis. This study was undertaken to evaluate the role of sema3A and NP-1 in the pathogenesis of systemic lupus erythematosus (SLE) and the specific effect of sema3A on the auto-reactive properties of B cells in SLE patients.

Methods

Thirty two SLE and 24 rheumatoid arthritis (RA) patients were assessed and compared with 40 normal individuals. Sema3A serum levels were measured and correlated with SLE disease activity. The in vitro effect of sema3A in reducing Toll-like receptor 9 (TLR-9) expression in B cells of SLE patients was evaluated.

Results

Sema3A serum levels in SLE patients were found to be significantly lower than in RA patients (55.04 ± 16.30 ng/ml versus 65.54 ± 14.82 ng/ml, P = 0.018) and lower yet than in normal individuals (55.04 ± 16.30 ng/ml versus 74.41 ± 17.60 ng/ml, P < 0.0001). Altered serum sema3A levels were found to be in inverse correlation with SLE disease activity, mainly with renal damage. The expression of both sema3A and NP-1 on B cells from SLE patients was significantly different in comparison with normal healthy individuals. Finally, when sema3A was co-cultured with cytosine-phosphodiester-guanine oligodeoxynucleotides (CpG-ODN)-stimulated B cells of SLE patients, their TLR-9 expression was significantly reduced, by almost 50% (P = 0.001).

Conclusions

This is the first study in which a reduced serum level of sema3A was found in association with SLE disease activity. It also raises the possibility that sema3A may have a regulatory function in SLE.     

Semaphorin-3A and semaphorin-3F work together to repel endothelial cells and to inhibit their survival by induction of apoptosis

Semaphorin-3A (sema3A) is a neuropilin-1 (np1) agonist. It inhibits the binding of the 165-amino acid form of VEGF (VEGF(165)) to np1 and was reported to inhibit angiogenesis as a result. However, we find that sema3A concentrations that inhibit the mitogenic effects of VEGF(165) do not inhibit VEGF(165)-induced phosphorylation of VEGF receptor-2 (VEGFR-2). Furthermore, sema3A inhibits the biological effects of VEGF(121), a VEGF form that does not bind to neuropilins and basic fibroblast growth factor, a growth factor whose activity, unlike that of VEGF, is not inhibited by small interfering RNA directed against np1. Therefore, the mechanism by which sema3A inhibits VEGF(165) activity does not depend on competition with VEGF(165) for binding to np1. Sema3A induced rapid disappearance of focal contacts followed by collapse of the actin cytoskeleton in human umbilical vein-derived endothelial cells. HEK293 cells expressing sema3A repel human endothelial cells and at high concentrations induce their death by apoptosis. Furthermore, sema3A inhibited the formation of tubes from endothelial cells in an in vitro angiogenesis assay. Similar effects are induced by the neuropilin-2 (np2) agonist sema3F. These inhibitory effects are abrogated by small interfering RNAs directed against np1 or np2, respectively. The anti-proliferative effects of sema3A and sema3F are additive when the semaphorins are added as pure proteins. However, when sema3A and sema3F were co-expressed in HEK293 cells their pro-apoptotic and cell repellant activities appeared to be synergistic. These observations suggest that combinations of sema3A and sema3F may be able to inhibit tumor angiogenesis more effectively than single semaphorins.     

Semaphorin 4D Promotes Skeletal Metastasis in Breast Cancer

Bone density is controlled by interactions between osteoclasts, which resorb bone, and osteoblasts, which deposit it. The semaphorins and their receptors, the plexins, originally shown to function in the immune system and to provide chemotactic cues for axon guidance, are now known to play a role in this process as well. Emerging data have identified Semaphorin 4D (Sema4D) as a product of osteoclasts acting through its receptor Plexin-B1 on osteoblasts to inhibit their function, tipping the balance of bone homeostasis in favor of resorption. Breast cancers and other epithelial malignancies overexpress Sema4D, so we theorized that tumor cells could be exploiting this pathway to establish lytic skeletal metastases. Here, we use measurements of osteoblast and osteoclast differentiation and function in vitro and a mouse model of skeletal metastasis to demonstrate that both soluble Sema4D and protein produced by the breast cancer cell line MDA-MB-231 inhibits differentiation of MC3T3 cells, an osteoblast cell line, and their ability to form mineralized tissues, while Sema4D-mediated induction of IL-8 and LIX/CXCL5, the murine homologue of IL-8, increases osteoclast numbers and activity. We also observe a decrease in the number of bone metastases in mice injected with MDA-MB-231 cells when Sema4D is silenced by RNA interference. These results are significant because treatments directed at suppression of skeletal metastases in bone-homing malignancies usually work by arresting bone remodeling, potentially leading to skeletal fragility, a significant problem in patient management. Targeting Sema4D in these cancers would not affect bone remodeling and therefore could elicit an improved therapeutic result without the debilitating side effects.     

Semaphorin4D的作用机制与功能

Semaphorins家族是一类以结构中具有sema区域为共同特征的蛋白,Semaphorin4D(Sema4D)是其成员之一.Sema4D与受体丛状蛋白B1(PlexinB1)和分化抗原簇72(cluster of differentiation antigen72,CD72)结合,通过多种信号转导途径,在神经系统的轴突导向,免疫系统中T、B细胞的活化和免疫调节中发挥关键作用.最近发现,Sema4D在许多人体肿瘤组织中高表达,且对血管发生及肿瘤侵袭转移起重要作用.本文旨在对Sema4D的结构、作用机制及生物学功能的研究最新进展作一综述.     

The action of Semaphorin7A on thalamocortical axon branching

Developing axons form extensive branches to make synaptic contacts with their target cells. Despite the important role of axon branching in neural circuit formation, its underlying molecular mechanism is still largely unknown. In this study, we investigated the involvement of Semaphorin7A (Sema7A) in thalamocortical (TC) axon branching. In situ hybridization demonstrated that sema7a was expressed specifically in layer 4, the TC recipient layer, when TC axons form extensive arbors. A similar protein expression pattern was observed by immunohistochemistry with an anti-Sema7A antibody. The effect of Sema7A on axon branching was investigated in dissociated cell cultures from embryonic rat thalamus. TC axon branching increased dramatically on Sema7A-coated dishes. We further studied the activity of Sema7A in vivo using loss- and gain-of-function analyses. The number of vesicular glutamate transporter 2-positive puncta was markedly reduced in the Sema7A-deficient cortex. In contrast, their number increased significantly when Sema7A was over-expressed in layer 4 cells by in utero electroporation. Taken together, these findings suggest that Sema7A acts as a positive regulator for TC axon branching and/or pre-synaptic puncta formation.     

The role of semaphorin3A in myogenic regeneration and the formation of functional neuromuscular junctions on new fibres

Current research on skeletal muscle injury and regeneration highlights the crucial role of nerve–muscle interaction in the restoration of innervation during that process. Activities of muscle satellite or stem cells, recognized as the ‘currency’ of myogenic repair, have a pivotal role in these events, as shown by ongoing research. More recent investigation of myogenic signalling events reveals intriguing roles for semaphorin3A (Sema3A), secreted by activated satellite cells, in the muscle environment during development and regeneration. For example, Sema3A makes important contributions to regulating the formation of blood vessels, balancing bone formation and bone remodelling, and inflammation, and was recently implicated in the establishment of fibre‐type distribution through effects on myosin heavy chain gene expression. This review highlights the active or potential contributions of satellite‐cell‐derived Sema3A to regulation of the processes of motor neurite ingrowth into a regenerating muscle bed. Successful restoration of functional innervation during muscle repair is essential; this review emphasizes the integrative role of satellite‐cell biology in the progressive coordination of adaptive cellular and tissue responses during the injury‐repair process in voluntary muscle.     

Endothelial Semaphorin 3fb regulates Vegf pathway-mediated angiogenic sprouting

Vessel growth integrates diverse extrinsic signals with intrinsic signaling cascades to coordinate cell migration and sprouting morphogenesis. The pro-angiogenic effects of Vascular Endothelial Growth Factor (VEGF) are carefully controlled during sprouting to generate an efficiently patterned vascular network. We identify crosstalk between VEGF signaling and that of the secreted ligand Semaphorin 3fb (Sema3fb), one of two zebrafish paralogs of mammalian Sema3F. The sema3fb gene is expressed by endothelial cells in actively sprouting vessels. Loss of sema3fb results in abnormally wide and stunted intersegmental vessel artery sprouts. Although the sprouts initiate at the correct developmental time, they have a reduced migration speed. These sprouts have persistent filopodia and abnormally spaced nuclei suggesting dysregulated control of actin assembly. sema3fb mutants show simultaneously higher expression of pro-angiogenic (VEGF receptor 2 (vegfr2) and delta-like 4 (dll4)) and anti-angiogenic (soluble VEGF receptor 1 (svegfr1)/ soluble Fms Related Receptor Tyrosine Kinase 1 (sflt1)) pathway components. We show increased phospho-ERK staining in migrating angioblasts, consistent with enhanced Vegf activity. Reducing Vegfr2 kinase activity in sema3fb mutants rescues angiogenic sprouting. Our data suggest that Sema3fb plays a critical role in promoting endothelial sprouting through modulating the VEGF signaling pathway, acting as an autocrine cue that modulates intrinsic growth factor signaling.