Takada N, Tagawa K, Takahashi H, Satoh N
Department of Zoology, Graduate School of Science, Kyoto University, Japan.
Int J Dev Biol. 1998 Nov;42(8):1093-100.
The T-box genes encode a novel family of transcriptional factors that seem to play crucial roles in various processes of animal development, in particular, mesoderm formation of chordate embryos. The ascidian egg has been regarded as a typical mosaic egg, in which several types of embryonic cells are specified autonomously dependent on prelocalized maternal factors or determinants. In the present study, we investigated a possible role of a maternal T-box gene (As-mT) of the ascidian Halocynthia roretzi. A cDNA clone we obtained predicted As-mT protein of 891 amino acids with a distinct T-domain, which was divergent from those of other T-box genes. Expression of As-mT was exclusively maternal. Although the transcript became barely detectable by the gastrula stage, no zygotic expression was evident during embryogenesis. The maternal transcript was distributed rather evenly within eggs and early embryos without any special localization. Injection of synthetic As-mT mRNA into fertilized eggs induced retardation of embryogenesis. Although cleavage occurred normally, the initiation of gastrulation was delayed, and delay in the morphogenesis resulted in dumpy larvae. Expression of a muscle-specific actin gene, a notochord-specific Brachyury gene, and an epidermis-specific gene was not detected at the early gastrula stage, all of the three genes being expressed in normal embryos at that stage. However, the expression of these genes as well as a mesenchyme-specific gene and histochemical activity of endoderm-specific alkaline phosphatase were evident by the mid-tailbud stage.
T-box基因编码一类新的转录因子家族，它们似乎在动物发育的各种过程中发挥关键作用，特别是在脊索动物胚胎的中胚层形成过程中。海鞘卵一直被视为典型的镶嵌卵，其中几种类型的胚胎细胞是自主特化的，依赖于预先定位的母体因子或决定因素。在本研究中，我们调查了海鞘柄海鞘母体T-box基因（As-mT）的可能作用。我们获得的一个cDNA克隆预测As-mT蛋白有891个氨基酸，带有一个独特的T结构域，这与其他T-box基因的结构域不同。As-mT的表达完全是母体性的。尽管在原肠胚阶段转录本几乎检测不到，但在胚胎发生过程中没有明显的合子表达。母体转录本在卵和早期胚胎中分布相当均匀，没有任何特殊定位。将合成的As-mT mRNA注射到受精卵中会导致胚胎发育迟缓。虽然卵裂正常发生，但原肠胚形成的起始延迟，形态发生的延迟导致幼虫短小。在早期原肠胚阶段未检测到肌肉特异性肌动蛋白基因、脊索特异性Brachyury基因和表皮特异性基因的表达，而这三个基因在该阶段的正常胚胎中均有表达。然而，到尾芽中期，这些基因以及间充质特异性基因的表达和内胚层特异性碱性磷酸酶的组织化学活性都很明显。
