| Co-Investigator(Kenkyū-buntansha) |
KUBO Yoshihiro Tokyo Metropolitan Institute for Neurosciences, Research Scientist, 神経生理, 研究員 (80211887)
OKAMURA Yasushi Faculty of Medicine, Department of Neurophysiology, Institute of Brain Res., Uni, 医学部(医), 助手 (80201987)
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| Research Abstract |
As previously reported, when the Halocynthia embryo, a protochordate, is cleavage-arrested at early developmental stages, 1- to 4-cell, and cultured further until the normal hatching time, the membrane of the large blastomeres expresses exclusively the epidermal-type excitability, while when cleavage-arrested after 8-cell stage, some of blastomeres show neural-type excitability. The difference can be caused by further segregation of egg cytoplasmic factors and/or cell-cell interaction after 8-cell stage. In the present project, a single anterior-animal blastomere which includes the presumptive neural region in the 8-cell embryo, when dissociated, cleavage-arrested and cultured in solution, differentiated exclusively to epidermal type judging from membrane excitability and immunoreactivity. However, when the same blastomere was cultured in contact with a single anterior-vegetal blastomere which includes the presumptive notochordal region, it displayed Na spikes, characterized by Na and
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K channels, and showed no expression of the epidermal antigen, suggesting "neural induction" resulted in a single cell during the interaction with a single neighboring cell. The contact necessary for this inductive interaction between an anterior-animal blastomere and an anterior-vegetal blastomere had a critical period before and after which the contact became ineffective and the period was between 64-cell stage and mid-gastrula stage of the control embryo. Further, some agents which mimic the inductive effects upon the anterior-animal blastomere were looked for and a proteolytic enzyme was found to develop Na spikes exactly identical with those induced by the cell-cell contact. Finally studying the mammalian embryonic system in comparison with the protochordate inductive system, the stem cells of cloned teratocarcinoma cell line derived from the primitive ectoderm of the 5 day mouse embryo was chemically induced to differentiate into neurons. The early stage of neural differentiation was characterized by expression of Na channels, T-type Ca channels, and 160 kD neurofilament protein in a round cell without neurite extension. Less
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