cAMP-Induced Expression of Neuropilin1 Promotes Retinal Axon Crossing in the Zebrafish Optic Chiasm
cAMP-Induced Expression of Neuropilin1 Promotes Retinal Axon Crossing in the Zebrafish Optic Chiasm
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cAMP 诱导的 Neuropilin1 表达促进斑马鱼视交叉视网膜轴突交叉
DOI：
10.1523/jneurosci.0197-13.2013
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发表时间：
2013-07-03
影响因子：
5.3
通讯作者：
Raper, Jonathan A.
中科院分区：
文献类型：
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作者：
Dell, Alison L.;Fried-Cassorla, Emma;Raper, Jonathan A.
生长中的轴突在复杂的环境中导航，因为它们会对吸引和排斥的引导线索做出反应。轴突可以通过G蛋白偶联的cAMP依赖性信号通路调节它们对线索的反应。为了研究G蛋白信号在体内轴突导向中的作用，我们使用GAL 4/UAS系统来驱动显性负性异源三聚体G蛋白（DNG）在胚胎斑马鱼视网膜神经节细胞（RGC）中的表达。视网膜轴突通常在腹侧中线交叉并投射到对侧顶盖。DNGαS在RGCs中的表达导致视网膜轴突错误投射到同侧顶盖。这些错误类似于adcy 1、adcy 8、nrp 1a、sema 3D或sema 3E变形胚胎以及sema 3D突变胚胎中的错误投射。nrp 1a在RGC中表达，因为它们的轴突朝向中线延伸并穿过中线。sema 3D和sema 3E在视交叉附近表达，表明它们促进视网膜中线穿越。我们证明了adcy 8敲低和转基因DNGαS表达、adcy 8和nrp 1a变形子或nrp 1a变形子和转基因DNGαS表达之间的同侧错误投射的协同诱导。使用qPCR分析，我们发现转基因DNGα S表达胚胎或adcy 8 morphant胚胎的nrp 1a和nrp 1b mRNA水平降低。adcy 8 morphants中的同侧错误投射通过在RGC中表达的nrp 1a拯救构建体的表达来校正。这些发现与这样的观点一致，即升高的cAMP水平促进RGCs中的Neuropilin 1a表达，增加视网膜轴突对中线处的Sema 3D、Sema 3E或其他Neuropilin配体的敏感性，从而促进视网膜轴突在视交叉中穿过。
Growing axons navigate a complex environment as they respond to attractive and repellent guidance cues. Axons can modulate their responses to cues through a G-protein-coupled, cAMP-dependent signaling pathway. To examine the role of G-protein signaling in axon guidance in vivo, we used the GAL4/UAS system to drive expression of dominant-negative heterotrimeric G-proteins (DNG) in retinal ganglion cells (RGCs) of embryonic zebrafish. Retinal axons normally cross at the ventral midline and project to the contralateral tectum. Expression of DNGαS in RGCs causes retinal axons to misproject to the ipsilateral tectum. These errors resemble misprojections in adcy1, adcy8, nrp1a, sema3D, or sema3E morphant embryos, as well as in sema3D mutant embryos. nrp1a is expressed in RGCs as their axons extend toward and across the midline. sema3D and sema3E are expressed adjacent to the chiasm, suggesting that they facilitate retinal midline crossing. We demonstrate synergistic induction of ipsilateral misprojections between adcy8 knockdown and transgenic DNGαS expression, adcy8 and nrp1a morphants, or nrp1a morphants and transgenic DNGαS expression. Using qPCR analysis, we show that either transgenic DNGαS-expressing embryos or adcy8 morphant embryos have decreased levels of nrp1a and nrp1b mRNA. Ipsilateral misprojections in adcy8 morphants are corrected by the expression of an nrp1a rescue construct expressed in RGCs. These findings are consistent with the idea that elevated cAMP levels promote Neuropilin1a expression in RGCs, increasing the sensitivity of retinal axons to Sema3D, Sema3E, or other neuropilin ligands at the midline, and consequently facilitate retinal axon crossing in the chiasm.