IN VIVO ANALYSIS OF SEMAPHORIN GENE FAMILY IN EARLY NEURAL NETWORK DEVELOPMENT

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Semaphorin gene family encodes secreted and transmembrane proteins and several members of this family have been shown to navigate specific growth cones in repulsive or attractive manner. We found zebrafish sema3A1 is expressed by dorsal and ventral myotomal cells. It repulses primary motor growth cones to navigate them toward a choice point where instruction events are suggested. After reaching the choice point, they pause for a while, then move into sema3A1 expressing region. At this region the primary motor axons begins to branch for making synapses with myotomal cells. By manipulating sema3A1 expression, we examined if it affects axon branching as well as navigating growth cones.In this study, we show the primary growth cones are repulsed by sema3A1 initially, but not after reaching the choice point. On the other hand, number of axonal branching increases by sema3A1 over-expression, that is independent upon growth cones location throughout their pathway. These results indicate that sema3A1 plays roles in both growth cone repulsion and axonal branching, that are regulated in different manners.