| Budget Amount *help |
¥1,700,000 (Direct Cost: ¥1,700,000)
Fiscal Year 2000: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1999: ¥1,200,000 (Direct Cost: ¥1,200,000)
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| Research Abstract |
The analysis on the endoderm formation after blastoderm stage of the chick embryo showed that new endoderm originating from the epiblast appears at the posterior end of the area pellucida and expands anteriorly as the primitive streak elongates, and endodermal cells from Hensen s node also migrate anteriroly. This suggested that both these two endoderms may contribute to the embryonic (gut) endoderm, differently from the previous notion. The induction of ectopic streak in the anterior epiblast of the chick embryo by local application of activin was confirmed, and the marking experiment revealed the localization of streak-forming cells rather distant from the activin-applied site, which suggested that activin may elicit streak-formation indirectly by inducing endogenous streak-inducible factor(s) in cells near the activinapplied site. However, anterior migration of endodermal cells from the node of the induced streak as seen iii normal development was found, suggesting the formation of
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the embryonic endoderm. Cultivation of anterior blastoderm fragments after activin-treatment confirmed rough dose-dependent induction of various mesodermal tissues, which does not contradict the probalbe indirect action of activin. Since blastoderm fragments as well as tissues containing no apparent endodermal tissues taken from primitive streak-stage embryos were found to develop gut endoderm without activin treatment in this experiment, the endoderm formation from the epiblast or other non-endodermal tissues by activin-treatment could not be proven. Massive appearance of various gut epitheia in activin-treated samples developing notochord may suggest de novo endoderm formation, but it is also possible that the notochord may elicit differentiation of various gut epithelia in the endoderm of hypoblast, whose possibility was recently shown by the present author s another experiment. Insulin-expressing pancreas-like structure developed after treatment with high concentration of activin may indicate the involvement of activin in pancreatic endodermal commitment. Less
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