Kurita Yoshihisa, Deguchi Ryusaku, Wada Hiroshi
Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba 305-8572, Japan.
Zoolog Sci. 2009 Dec;26(12):814-20. doi: 10.2108/zsj.26.814.
Despite easy access to bivalves, few studies have examined the development of these animals, at least in part because most bivalve eggs are very small. In addition, annotating cells of the early bivalve embryo is difficult because few landmarks are present. We conducted detailed cell annotations of the Japanese purple mussel, Septifer virgatus, during early embryogenesis because of its relatively large eggs (ca. 130 microm in diameter). Septifer virgatus underwent the unique cell division profile reported for four other bivalve species, suggesting that the cleavage pattern itself is important for bivalve morphogenesis. The shell field invagination was led by 2d (X) lineage cells, supporting the hypothesis that lineage cells differentiate into cells excreting the shell matrix. The large egg size enabled us to trace cell movements in the early gastrulation phase, during which the invagination of the archenteron was initiated by 4d (M) lineage cells. These observations will serve as a basis for future analyses of S. virgatus embryogenesis and will contribute to understanding the evolution of the molluscan body plan, which is achieved by modification of early embryogenesis.
尽管双壳贝类很容易获取，但很少有研究对这些动物的发育进行研究，至少部分原因是大多数双壳贝类的卵非常小。此外，对双壳贝类早期胚胎的细胞进行注释很困难，因为几乎没有可用的标志性特征。由于日本紫贻贝（Septifer virgatus）的卵相对较大（直径约130微米），我们在其早期胚胎发育过程中对其进行了详细的细胞注释。Septifer virgatus呈现出其他四种双壳贝类物种所报道的独特细胞分裂模式，这表明卵裂模式本身对双壳贝类的形态发生很重要。壳场内陷由2d（X）谱系细胞引导，支持了谱系细胞分化为分泌壳基质细胞的假说。较大的卵尺寸使我们能够追踪原肠胚形成早期阶段的细胞运动，在此期间，原肠的内陷由4d（M）谱系细胞启动。这些观察结果将为未来对Septifer virgatus胚胎发育的分析奠定基础，并将有助于理解通过早期胚胎发育的改变而实现的软体动物身体结构的进化。
