Regulatory mechanism of expression of inducing factors in early embryognesis

在非洲爪蟾胚胎发生过程中，细胞间的相互作用是模式形成的关键，其中TGF-β超家族和FGF家族成员等生长因子在模式形成过程中发挥着重要作用。在TGF-β超家族成员中，激活素已知是两栖动物胚胎中最有效的因子之一。为了获得理解激活素作用的线索，特别是为了阐明其活性的发育控制，我们从某些方面研究了激活素和两种激活素结合蛋白，激活素受体和卵泡抑素，并获得了如下所述的结果。1)从它们的空间表达模式的分析中，发现只有folistatin mRNA表现出相当有限的表达模式，表明folistain可能具有限制胚胎发生中激活素活性的功能。2）为了分析卵泡抑素表达调控的分子机制，我们克隆了卵泡抑素基因，并测定了其核苷酸序列。3)通过显微注射激活素受体的野生型和显性负型，我们研究了激活素的功能和卵裂球对激活素的感受性。结果表明，激活素系统在中胚层的诱导中起重要作用，在卵裂早期，每个卵裂球对激活素的反应能力不同。

In Xenopus laevis embryogenesis, cell-cell interactions are essential for patern formation, in which several growth factors such as TGF-beta superfamily and FGF family members have been shown to play important functions. Among TGF-beta superfamily members, activin has been known to be one of the most potent in amphibian embryos. In order to obtain a clue to understanding the roles of activin and especially to clarify developmental control of its activity, we examined activin and two activin-binding proteins, activin receptors and follistatin with some aspects and obtained the results as described below. 1)From the analysis of their spatial expression pattern, it is found that only folistatin mRNA showed quite a restricted pattern of expression, indicating that follistain may have a function for the restriction of activin activity in embryogenesis. 2)To analyze the molecular mechanism of the regulation of follistatin expression, we isolated the follistatin gene and determined its nucleotide sequence. 3)Using microinjection of wild-type and dominant negative type of activin receptor, we examined the functin of activin and the competence of blastomeres for activin. The results suggested that activin system plays important function in mesoderm induction and that each blastomeres at early cleavage stage has different competence for activin.