Post-crossing segment of dI1 commissural axons forms collateral branches to motor neurons in the developing spinal cord
Post-crossing segment of dI1 commissural axons forms collateral branches to motor neurons in the developing spinal cord
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dI1 连合轴突的交叉后段形成发育中脊髓中运动神经元的侧支
DOI：
10.1002/cne.24464
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发表时间：
2018
期刊：
影响因子：
--
通讯作者：
Ryuichi Shirasaki
中科院分区：
文献类型：
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作者：
Takeshi Kaneyama;Ryuichi Shirasaki
发育中的脊髓中的dI 1连合轴突，在穿过底板的中线时，急转而向吻侧生长。这些交叉轴突最初只是延伸到地板附近，而不进入附近的运动柱。然而，它仍然很差的特点如何这些post-crossing dI 1轴突行为随后这一过程。在本研究中，为了解决这个问题，我们详细研究了小鼠中交叉后dI 1轴突的行为，使用Atoh 1增强子为基础的条件表达系统，可以选择性和稀疏标记单个dI 1轴突，以及Hb 9和ChAT免疫组织化学精确识别脊髓运动神经元（MN）。我们意外地发现，dI 1轴突的后交叉段后来发出侧支，这些侧支向外侧延伸，侵入运动柱。有趣的是，这些侧枝出现的时间大约是它们的初级生长锥开始侵入运动柱的时候。此外，虽然侧向生长的侧支的长度随着年龄的增长而增加，但它们中的大多数仍保持在运动柱内。引人注目的是，这些侧支进一步引起了多个二级分支在该地区的MN，神经支配肌肉接近体轴。此外，这些轴突分支在MN上形成突触前终末。这些观察结果表明，dI 1连合神经元通过随后从这些轴突的后交叉段产生的侧支发展轴突投射到脊髓MN。因此，我们的研究结果揭示了一个以前未被认识到的dI 1连合轴突的投影，可能直接有助于产生适当的运动输出。
The dI1 commissural axons in the developing spinal cord, upon crossing the midline through the floor plate, make a sharp turn to grow rostrally. These post‐crossing axons initially just extend adjacent to the floor plate without entering nearby motor columns. However, it remains poorly characterized how these post‐crossing dI1 axons behave subsequently to this process. In the present study, to address this issue, we examined in detail the behavior of post‐crossing dI1 axons in mice, using theAtoh1enhancer‐based conditional expression system that enables selective and sparse labeling of individual dI1 axons, together with Hb9 and ChAT immunohistochemistry for precise identification of spinal motor neurons (MNs). We found unexpectedly that the post‐crossing segment of dI1 axons later gave off collateral branches that extended laterally to invade motor columns. Interestingly, these collateral branches emerged at around the time when their primary growth cones initiated invasion into motor columns. In addition, although the length of the laterally growing collateral branches increased with age, the majority of them remained within motor columns. Strikingly, these collateral branches further gave rise to multiple secondary branches in the region of MNs that innervate muscles close to the body axis. Moreover, these axonal branches formed presynaptic terminals on MNs. These observations demonstrate that dI1 commissural neurons develop axonal projection to spinal MNs via collateral branches arising later from the post‐crossing segment of these axons. Our findings thus reveal a previously unrecognized projection of dI1 commissural axons that may contribute directly to generating proper motor output.