Abstract:Precardiac mesoderm (PCM) of chick embryo at stage 5 was excised with or without endoderm and ectoderm and cultured in vitro using Eagle's minimum essential medium (MEM) as a basic medium. PCM placed alone in MEM degenerated.When PCM was associated with endoderm, it produced beating tissue in MEM, while it did not show pulsation with ectoderm in the same condition. If MEM was supplemented with 15% horse serum, PCM developed into beating tissue without endoderm. Insulin (25 ug/m1) was effective in differentiation of PCM to myocardial cells.
We have found that precardiac mesoderm extirpated from chicken blastoderm at stage 5 fails to differentiate into beating tissue when cultured in Eagle's minimum essential medium (MEM), while it can pulsate provided either the endoderm is present or serum is added to the MEM. To identify the factor(s) which influence early myocardial differentiation, we examined the effect of insulin-like growth factor 1 (IGF-1), activin A and basic fibroblast growth factor (bFGF). All these growth factors showed a stimulating effect on myocardial differentiation and it is conceivable that these factors exhibit the same effect in vivo.
Fine structures were compared between normal pole cells and those induced in embryos that had been uv-irradiated and then injected with intact polar plasm or with poly(A)+RNA extracted from cleavage embryos. Nuclei in nomal pole cells were spherical. In contrast, those in the induced pole cells were deformed to variable extents depending on materials injected with. Polar granules were smaller in pole cells induced by injection of poly(A)+RNA than in normal pole cells. The size of polar granules in polar-plasminduced pole cells was intermediate between those in poly(A)+RNA-induced and normal pole cells. Small polar granules were observed in posterior cells of embryos uv-irradiated, nevertheless those cells were columnar and with identical morphology to somatic cells. Nuclear bodies showed a similar tendency in size differences as observed in polar granules in three types of pole cells observed.
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