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

信号蛋白基因家族编码分泌和跨膜蛋白，该家族的几个成员已被证明以排斥或吸引的方式引导特定的生长锥。我们发现斑马鱼的sema3A1在背侧和腹侧肌瘤细胞中表达。它排斥初级运动生长锥，引导它们走向一个建议指令事件的选择点。到达选择点后，它们会暂停一段时间，然后进入sema3A1表达区。在这个区域，初级运动轴突开始分支，与肌瘤细胞形成突触。通过操纵sema3A1表达，我们检查了它是否影响轴突分支以及生长锥的导航。在这项研究中，我们发现初生生长球果最初被sema3A1排斥，但在达到选择点之后就不会被排斥。另一方面，sema3A1的过表达增加了轴突分支的数量，这与生长锥在其通路中的位置无关。这些结果表明sema3A1在生长锥排斥和轴突分支中都起作用，但以不同的方式调节。

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.