Functional analysis of cnil ; an intra-cellular transporter of EGF-repeat-containing growth factors

在向外周迁移的过程中，颅神经嵴细胞（NCCs）被相邻的间质斜形神经粒(r) 3和5中的erbb4依赖信号所排斥，这些斜形神经粒是分节的后脑神经粒。ErbB4有许多配体，但在上述体系中究竟是哪一种配体起作用还没有明确的确定。本研究发现，在发育中的小鸡r3和r5中表达了一个cornicon样蛋白/ cornicon同源基因2 （CNIL/CNIH2）。在细胞培养系统中，其产物促进ErbB4配体之一的肝素结合表皮生长因子样生长因子（HB-EGF）的分泌。当鸡胚中CNIL的功能被强迫表达截断后的CNIL干扰时，NCCs的分布受到影响，导致颅神经节、感觉神经节之间的神经纤维连接异常。同样，用sirna敲除CNIL或HB-EGF也会产生类似的表型。这种表型与ErbB4敲除（KO）小鼠胚胎非常相似。由于HB-EGF在胚胎后脑中均匀表达，CNIL似乎将HB-EGF的作用位点限制在r3和r5，并与ErbB4一致。

During their migration to the periphery, cranial neural crest cells (NCCs) are repulsed by an ErbB4-dependent cue(s) in the mesenchyme adjoining rhombomeres (r) 3 and 5, which are segmented hindbrain neuromeres. ErbB4 has many ligands, but which ligand functions in the above system has not yet been clearly determined. Here we found that a cornichon-like protein/cornichon homolog 2 (CNIL/CNIH2) gene was expressed in the developing chick r3 and r5. In a cell culture system, its product facilitated the secretion of heparin-binding epidermal growth factor-like growth factor (HB-EGF), one of the ligands of ErbB4. When CNIL function was perturbed in chick embryos by forced expression of a truncated form of CNIL, the distribution of NCCs was affected, which resulted in abnormal nerve fiber connections among the cranial, sensory ganglia. Also, knockdown of CNIL or HB-EGF with siRNAs yielded a similar phenotype. This phenotype closely resembled that of ErbB4 knockout (KO) mouse embryos. Since HB-EGF was uniformly expressed in the embryonic hindbrain, CNIL seems to confine the site of HB-EGF action to r3 and r5 in concert with ErbB4.