Curran Bridget M, Nickerson Kelsey R, Yung Andrea R, Goodrich Lisa V, Jaworski Alexander, Tessier-Lavigne Marc, Ma Le
Department of Neuroscience, Jefferson Synaptic Biology Center, Vickie and Jack Farber Institute for Neuroscience, Sydney Kimmel Medical College, Thomas Jefferson University, Philadelphia, PA 19107.
Department of Neuroscience, Brown University, Providence, RI 02912.
bioRxiv. 2024 Apr 15:2023.11.17.567638. doi: 10.1101/2023.11.17.567638.
The dorsal funiculus in the spinal cord relays somatosensory information to the brain. It is made of T-shaped bifurcation of dorsal root ganglion (DRG) sensory axons. Our previous study has shown that Slit signaling is required for proper guidance during bifurcation, but loss of Slit does not affect all DRG axons. Here, we examined the role of the extracellular molecule Netrin-1 (Ntn1). Using wholemount staining with tissue clearing, we showed that mice lacking Ntn1 have axons escaping from the dorsal funiculus at the time of bifurcation. Genetic labeling confirmed that these misprojecting axons come from DRG neurons. Single axon analysis showed that loss of Ntn1 does not affect bifurcation but rather alters turning angles. To distinguish their guidance functions, we examined mice with triple deletion of Ntn1, Slit1, and Slit2 and found a completely disorganized dorsal funiculus. Comparing mice with different genotypes using immunolabeling and single axon tracing revealed additive guidance errors, demonstrating the independent roles of Ntn1 and Slit. Moreover, the same defects were observed in embryos lacking their cognate receptors. These studies thus demonstrate the presence of multi-factorial guidance mechanisms that ensure proper formation of a common branched axonal structure during spinal cord development.
脊髓中的背侧索将躯体感觉信息传递至大脑。它由背根神经节（DRG）感觉轴突的T形分支构成。我们之前的研究表明，在分支形成过程中，Slit信号对于正确引导是必需的，但Slit缺失并不影响所有DRG轴突。在此，我们研究了细胞外分子Netrin-1（Ntn1）的作用。通过组织透明化的整体染色，我们发现缺乏Ntn1的小鼠在分支形成时轴突从背侧索逃逸。基因标记证实这些投射错误的轴突来自DRG神经元。单轴突分析表明，Ntn1缺失并不影响分支形成，而是改变转向角度。为了区分它们的引导功能，我们研究了同时缺失Ntn1、Slit1和Slit2的小鼠，发现背侧索完全紊乱。通过免疫标记和单轴突追踪比较不同基因型的小鼠，发现引导错误具有累加性，这证明了Ntn1和Slit的独立作用。此外，在缺乏其同源受体的胚胎中也观察到了相同的缺陷。因此，这些研究证明了存在多因素引导机制，以确保在脊髓发育过程中共同分支轴突结构的正确形成。
