Robo2–Slit and Dcc–Netrin1 Coordinate Neuron Axonal Pathfinding within the Embryonic Axon Tracts
Robo2–Slit and Dcc–Netrin1 Coordinate Neuron Axonal Pathfinding within the Embryonic Axon Tracts
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DOI：
10.1523/jneurosci.6518-11.2012
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发表时间：
2012-09
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影响因子：
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通讯作者：
Changwen Zhang;Jingxia Gao;Hefei Zhang;Liu Sun;G. Peng
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作者：
Changwen Zhang;Jingxia Gao;Hefei Zhang;Liu Sun;G. Peng
在胚胎脊椎动物大脑中，早期出生的神经元建立了高度定型的胚胎轴突束，神经元互连沿着该轴突束形成。为了了解轴突束胚胎支架内神经元轴突寻路的机制，我们研究了斑马鱼前背侧端脑（ADt）神经元发育。虽然之前的研究表明 ADt 神经元轴突沿着连合束 [前连合 (AC)] 和同侧下降束 [视上束 (SOT)] 延伸，但尚不清楚单个 ADt 神经元轴突是否在 AC 和 SOT 交叉点处选择特定的投影路径。我们使用前脑特异性启动子来标记单个 ADt 神经元，以驱动荧光蛋白的表达。我们发现 ADt 轴突投影模式是异质的并且与其体细胞位置相关。我们的结果表明，沿端脑背腹轴的细胞内在差异调节轴突投射的选择。接下来，我们确定结直肠癌中的引导受体 roundabout2 (Robo2) 和缺失 (Dcc) 在 ADt 神经元中存在差异表达。我们发现，通过注射反义吗啉寡核苷酸来敲除 Robo2 功能，可以消除源自 ADt 神经元的同侧 SOT。关闭 Dcc 功能并不能阻止 AC 和 SOT 的形成。相比之下，当 Netrin1 功能被敲除时，AC 会明显降低。进一步的机制研究表明，Robo2 对排斥性的 Slit 信号做出反应，并抑制有吸引力的 Netrin 信号。这些发现证明了 Robo2-Slit 和 Dcc-Netrin 如何协调脊椎动物前脑中发育中神经元的轴突投射选择。
In the embryonic vertebrate brain, early born neurons establish highly stereotyped embryonic axonal tracts along which the neuronal interconnections form. To understand the mechanism underlying neuron axonal pathfinding within the embryonic scaffold of axon tracts, we studied zebrafish anterior dorsal telencephalic (ADt) neuron development. While previous studies suggest the ADt neuronal axons extend along a commissural tract [anterior commissure (AC)] and a descending ipsilateral tract [supraoptic tract (SOT)], it is unclear whether individual ADt neuronal axons choose specific projection paths at the intersection between the AC and the SOT. We labeled individual ADt neurons using a forebrain-specific promoter to drive expression of fluorescent proteins. We found the ADt axonal projection patterns were heterogeneous and correlated with their soma positions. Our results suggest that cell intrinsic differences along the dorsal ventral axis of the telencephalon regulate the axonal projection choices. Next, we determined that the guidance receptors roundabout2 (Robo2) and deleted in colorectal cancer (Dcc) were differentially expressed in the ADt neurons. We showed that knocking down Robo2 function by injecting antisense morpholino oligonucleotides abolished the ipsilateral SOT originating from the ADt neurons. Knocking down Dcc function did not prevent formation of the AC and the SOT. In contrast, the AC was specifically reduced when Netrin1 function was knocked down. Further mechanistic studies suggested that Robo2 responded to the repellent Slit signals and suppressed the attractive Netrin signals. These findings demonstrate how Robo2–Slit and Dcc–Netrin coordinate the axonal projection choices of the developing neurons in the vertebrate forebrain.