Darras S, Nishida H
Department of Biological Sciences, Tokyo Institute of Technology, Nagatsuta, Midori-ku, Yokohama, 226-8501, Japan.
Dev Biol. 2001 Aug 15;236(2):271-88. doi: 10.1006/dbio.2001.0339.
We have investigated the role of the bone morphogenetic protein (BMP) pathway during neural tissue formation in the ascidian embryo. The orthologue of the BMP antagonist, chordin, was isolated from the ascidian Halocynthia roretzi. While both the expression pattern and the phenotype observed by overexpressing chordin or BMPb (the dpp-subclass BMP) do not suggest a role for these factors in neural induction, BMP/CHORDIN antagonism was found to affect neural patterning. Overexpression of BMPb induced ectopic sensory pigment cells in the brain lineages that do not normally form pigment cells and suppressed pressure organ formation within the brain. Reciprocally, overexpressing chordin suppressed pigment cell formation and induced ectopic pressure organ. We show that pigment cell formation occurs in three steps. (1) During cleavage stages ectodermal cells are neuralized by a vegetal signal that can be substituted by bFGF. (2) At the early gastrula stage, BMPb secreted from the lateral nerve cord blastomeres induces those neuralized blastomeres in close proximity to adopt a pigment cell fate. (3) At the tailbud stage, among these pigment cell precursors, BMPb induces the differentiation of specifically the anterior type of pigment cell, the otolith; while posteriorly, CHORDIN suppresses BMP activity and allows ocellus differentiation.
我们研究了骨形态发生蛋白（BMP）信号通路在海鞘胚胎神经组织形成过程中的作用。从海鞘柄海鞘中分离出了BMP拮抗剂脊索蛋白的同源物。虽然过表达脊索蛋白或BMPb（dpp亚类BMP）所观察到的表达模式和表型并不表明这些因子在神经诱导中起作用，但发现BMP/脊索蛋白拮抗作用会影响神经模式形成。过表达BMPb会在通常不形成色素细胞的脑谱系中诱导异位感觉色素细胞，并抑制脑内压力器官的形成。相反，过表达脊索蛋白会抑制色素细胞的形成并诱导异位压力器官。我们发现色素细胞的形成分三步进行。（1）在卵裂阶段，外胚层细胞通过一种可被碱性成纤维细胞生长因子替代的植物信号而神经化。（2）在原肠胚早期，从侧神经索卵裂球分泌的BMPb诱导紧邻的那些神经化卵裂球形成色素细胞命运。（3）在尾芽阶段，在这些色素细胞前体中，BMPb特异性地诱导前型色素细胞耳石的分化；而在后部，脊索蛋白抑制BMP活性并允许眼点分化。
