Nishimura Y, Wake K
Bull Tokyo Med Dent Univ. 1986 Jun;33(2):49-69.
In the early embryos of the ascidian (Halocynthia roretzi), regional cytoplasmic differences arise just after fertilization. We successively studied the characteristic features of the cytoplasm of those regions in the embryonic cells during the entire ontogenic process from the unfertilized egg to the tadpole larva. The embryos and larvae were fixed in a mixture of osmium and glutaraldehyde, and the distribution of the organelles in the entire cytoplasm was observed with light and electron microscopy. According to the analysis of the distribution density of the organelles which occupied a given area of the cytoplasm on the section, we introduced the "organelle region" in the cytoplasm and further calculated the approximate area ratios of the "organelle regions" in the cytoplasm of each cell lineage. As a result, it was demonstrated that the characteristic distribution mode was already present in the cytoplasm of the cell lineages of the 8-cell-stage embryos. The features of the cytoplasm in each embryonic cell lineage, moreover, reflected those of the corresponding larval tissue. Our results not only demonstrate that the structural tissue specificity is expressed at an extremely early stage during the ascidian embryogenesis but also suggest that the corresponding functional differentiation among the cell lineages occurs early.
在海鞘（柄海鞘）的早期胚胎中，受精后不久就会出现区域性的细胞质差异。我们相继研究了从未受精卵到蝌蚪幼虫的整个个体发育过程中，胚胎细胞中这些区域细胞质的特征。将胚胎和幼虫固定在锇和戊二醛的混合液中，通过光学显微镜和电子显微镜观察整个细胞质中细胞器的分布。根据对占据切片上细胞质给定区域的细胞器分布密度的分析，我们在细胞质中引入了“细胞器区域”，并进一步计算了每个细胞谱系细胞质中“细胞器区域”的近似面积比。结果表明，8细胞期胚胎的细胞谱系细胞质中已经存在特征性的分布模式。此外，每个胚胎细胞谱系的细胞质特征反映了相应幼虫组织的特征。我们的结果不仅表明结构组织特异性在海鞘胚胎发生的极早期就已表达，还表明细胞谱系之间相应的功能分化也很早就发生了。
