The Molecular Mechanism Involved in the Sensory Axonal Projection toward the Spinal Cord

在发育早期，中央突出的背根神经节（DRG）神经元轴突向脊髓背侧延伸。我们发现脊髓背侧的化学吸引参与了这一投射。然而，这种吸引力的分子性质尚不清楚。我们发现层粘连蛋白-1 （α1β1γ1）沿DRG轴突通路强烈表达，其67-kDa受体（67LR）存在于DRG细胞上。通过培养实验，我们发现层粘连蛋白-1或YIGSR肽（层粘连蛋白β1链的可溶性肽）促进DRG轴突对脊髓背源性化学吸引的反应。通过使用抗67LR的功能阻断抗体，我们发现抗67LR抗体在体外阻断了YIGSR肽对DRG轴突反应的调节。此外，卵内注射抗67lr抗体可抑制DRG轴突向脊髓背侧生长。这些结果证明，YIGSR肽通过67LR促进脊髓背源性化学吸引，有助于形成DRG轴突发育的初始轨迹。接下来，为了鉴定早期脊髓背侧差异表达的新基因，我们使用了Kazusa cDNA阵列系统和激光捕获显微解剖。我们观察到，在脊髓背侧有一定数量的基因表达显著增加。

During early development, centrally projecting dorsal root ganglion (DRG) neurons extend their axons toward the dorsal spinal cord. We found the involvement of dorsal spinal cord-derived chemoattraction in this projection. However, the molecular nature of this attraction is not clear. We showed that laminin-1 (α1β1γ1) is expressed strongly along the pathway of DRG axons and that its 67-kDa receptor (67LR) was present on DRG cells. By employing culture assays, we showed that laminin-1 or the YIGSR peptide, a soluble peptide of the laminin β1 chain, promoted the DRG axonal response to dorsal spinal cord-derived chemoattraction. By using a function-blocking antibody against 67LR, we showed that the anti-67LR antibody blocked the modulation of DRG axonal response by the YIGSR peptide in vitro. Furthermore, the in ovo injection of the anti-67LR antibody inhibited the DRG axonal growth, toward the dorsal spinal cord. These results provide evidence that the YIGSR peptide promotes dorsal spinal cord-derived chemoattraction via 67LR to contribute to the formation of the initial trajectories of developing DRG axons. Next, to identify novel genes differentially expressed in an early dorsal spinal cord, we used the Kazusa cDNA array system and laser capture microdissection. We observed that a certain population of genes showed significantly increased expression in the dorsal spinal cord.