Molecular mechanisms which control the cell movements during ascidian neural tube formation

点击翻译按钮获取中文摘要

Ascidian neural tube has basically the same structure as those of vertebrates. Its relatively simple structure and the abundant molecular resources of the ascidian offer an excellent experiment system for analyzing the molecular mechanisms of neural tube formation. However, according to our previous studies, the question has been raised as to whether or not the molecular mechanisms of vertebrate and ascidian neural tube formation are similar. So we reexamined the following two subjects.1.Reexamination of Ciona intestinalis Cadherin genes (CiCadI and CiCadII)We have already showed the neural-tube specific expression of CiCadII. We tried to analyze the spatial and temporal expression pattern of the other Ciona classic cadherin, Cadherin type I (CiCadI). Using the RT-PCR, CiCadI expressed maternally and its zygotic expression was detected from gastrula stage to the tailbud stage. This result suggested that, during the Ciona development, the two classic cadherin were used in the neural tube formation. The result that both CiCadI and CiCadII were used during the ascidian neural tube formation suggested the similarity in the molecular mechanisms of the ascidian and vertebrates neural tube formation.2.Reexamination of the cell movement during neural tube formationDuring the vertebrate neural tube formation, two types of mechanisms, primary-and secondary-neural tube formation, are proposed. In this study, we stained cortical actin network with phalloidin, and marked the neural tube cells, which carried GFP-reporter gene driven by the neural-tube specific promoter. The nerve-cord precursor cells actively moved posteriorly and made obvious cell rearrangement. On the other hand, brain-precursor cells did not move much along the anterior-posterior axis. The brain-stem precursor cells contained a certain amount of actin network. These regional differences suggested the different mechanism for each region within the neural tube.