Study on the cytoplasmic and inductive factors for the excitable membrane differentiation in the cleavage-arrested and isolated blastomeres of the early embryo.

据报道，当原脊索鱼胚胎的细胞分裂在发育早期被阻止时，如1-到8-细胞，并进一步培养到正常孵化时间，大的多核卵裂球的膜表达四种兴奋性类型之一，如神经、表皮、肌肉和非兴奋性类型。这表明，尽管卵裂球在正常发育过程中有多种命运，但卵裂球中的所有细胞核显然只选择一种细胞类型进行表达。在本研究项目中，这种选择通常被认为是细胞分化的重要机制之一。随后进行了两种实验。首先，研究了分离的8-细胞和卵裂停滞的卵裂球的细胞自主分化。其次，通过在发育过程中接触两种类型的卵裂球，研究了在与相邻细胞相互作用下的分化。8-细胞的前A42和后B42外胚层卵裂球诱发出持续时间较长的钙动作电位，抗表皮单抗2C5与其胞浆结合，提示在分离培养条件下发生了表皮型分化。相比之下，A42‘S在与A41卵裂球密切接触的情况下培养时，70%的受检病例产生了钠刺。在这种情况下，2C5没有结合到细胞质上，表明分化不是表皮类型。考虑到在脊椎动物胚胎中，含有假定脊索区的轴向中胚层可以诱导神经板，在本原索动物中，包括假定脑囊区的A42可能是由包含假定脊索区的A41诱导的，并分化为神经型。

As previously reported, when the cell-cleavage of the Halocynthia embryo of the protochordate is arrested at the early developmental stage, such as 1- to 8-cell, and the arrested embryo is cultured further until the normal hatching time, the membrane of a large and multinuclear blastomere expresses one of four types of excitability, such as neural, epidermal, muscular and non-excitable types. This suggests that all nuclei in the blastomere apparently select only one cell type for their expression though the blastomere has multiple fates during normal development. In this research project, this selection is presumed to be one of the important mechanisms for cellular differentiation in general. Following two kinds of experiments were performed. Firstly, the cell autonomous differentiation of the isolated and cleavage-arrested blastomeres of the 8-cell was studied. Secondly the differentiation under the interaction with neighboring cells was studied by contacting two types of the blastomere during development. The anterior a42 and posterior b42 ectodermal blastomeres of the 8-cell evoked a long-lasting Ca action potential and antiepidermal monoclonal antibody 2C5 was bound to their cytoplasm, suggesting the epidermal type differentiation when they were cultured in isolated condition. In contrast, the a42's produced Na spikes in 70% of all examined cases when they were cultured under close contact with the A41 blastomere. In this situation the 2C5 was not bound to the cytoplasm, suggesting the differentiation other than the epidermal type. Considering that in the case of vertebrate embryo's the axial mesoderm including the presumptive notochordal region can induce the neural plate, in this protochordate, an ancestoral form of the vertebrate, the a42 including presumptive brain vesicle region was inferred to be induced by the A41 including the presumptive notochordal region and to differentiate into neural type.