Akanuma Takashi, Hori Sawako, Darras Sébastien, Nishida Hiroki
Department of Biological Sciences, Tokyo Institute of Technology, Nagatsuta, Midori-ku, Yokohama 226-8501, Japan.
Dev Genes Evol. 2002 Nov;212(10):459-72. doi: 10.1007/s00427-002-0264-x. Epub 2002 Sep 7.
Notch signaling plays crucial roles during embryogenesis in various metazoans. HrNotch, a Notch homologue in the ascidian Halocynthia roretzi, has been previously cloned, and its expression pattern suggests that HrNotch signaling is involved in nervous system formation. To determine the function of HrNotch signaling, in the present study we examined the effects of the constitutively activated forms of HrNotch. Overexpression resulted in larvae with defects in neural tube closure and brain vesicle formation. In embryos expressing the activated HrNotch, the expression of a neural marker gene, HrETR-1, was enhanced and expanded in the central nervous system, although ectopic expression decreased during the tailbud stage. The activated HrNotch also suppressed the formation of the adhesive organ (palps) and the peripheral nervous system, which consists of ciliary mechanosensory neurons, whereas it promoted epidermal differentiation. The suppression and promotion of the formation of these respective cell types were confirmed by examination of the expression of relevant tissue-specific markers. We also cloned Hrdelta, an ascidian homologue of DSL family genes, which encode ligands for which Notch acts as a receptor. The expression of Hrdelta was observed in the precursors of palps and peripheral neurons in addition to the CNS. These results suggest that Notch signaling is important for ascidian nervous system formation and that it affects the fate choice between palps and epidermis and between peripheral neurons and epidermis within the neurogenic regions of the surface ectoderm by suppressing the formations of palps and peripheral neurons and promoting epidermal differentiation.
Notch信号通路在各种后生动物的胚胎发育过程中发挥着关键作用。HrNotch是海鞘Halocynthia roretzi中的一种Notch同源物，此前已被克隆，其表达模式表明HrNotch信号通路参与神经系统的形成。为了确定HrNotch信号通路的功能，在本研究中我们检测了组成型激活形式的HrNotch的作用。过表达导致幼虫出现神经管闭合和脑泡形成缺陷。在表达激活型HrNotch的胚胎中，一种神经标记基因HrETR-1的表达在中枢神经系统中增强并扩展，尽管在尾芽期异位表达减少。激活型HrNotch还抑制了黏附器官（触须）和由纤毛机械感觉神经元组成的外周神经系统的形成，而促进了表皮分化。通过检测相关组织特异性标记物的表达，证实了这些各自细胞类型形成的抑制和促进作用。我们还克隆了Hrdelta，它是DSL家族基因的海鞘同源物，该家族基因编码Notch作为受体的配体。除中枢神经系统外，在触须和外周神经元的前体中也观察到了Hrdelta的表达。这些结果表明，Notch信号通路对海鞘神经系统的形成很重要，并且它通过抑制触须和外周神经元的形成并促进表皮分化，影响表面外胚层神经源性区域内触须与表皮之间以及外周神经元与表皮之间的命运选择。
