DIFFERENTIAL INITIATION OF rRNA GENE ACTIVITY IN PROGENIES OF DIFFERENT BLASTOMERES OF EARLY XENOPUS EMBRYOS: EVIDENCE FOR REGULATED SYNTHESIS OF rRNA

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Abstract
The dorsal and ventral blastomeres of 4-celled embryos of X. laevis were separated. During the next 14 h in culture the cell numbers of the progeny cell aggregates of the dorsal and ventral blastomeres, respectively, were the same. Synthesis of 4 S RNA started after about 4 h of culture in both kinds of progeny cell aggregates. A difference was found in the time when rRNA synthesis started in these aggregates: it began after 10 h in cell aggregates derived from the dorsal blastomeres, and after about 14 h in those derived from the ventral blastomeres. After this, rRNA synthesis became more active in both types of aggregates. This is the 1st demonstration of differential initiation of rRNA synthesis in aggregates derived from different blastomeres but containing the same number of cells. There is developmental regulation of rRNA synthesis.
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