Expression of Ribosomal Protein Genes in Xenopus Development
Ribosome production is one of the major projects of developmental systems, such as Xenopus oocytes and embryos, which thus are particularly suitable for the investigation of the regulation of ribosome biogenesis. A typical feature of the embryo is its utilization of maternal stored material accumulated during the oogenesis. In particular the Xenopus embryo is completely dependent on maternal gene products until the ‘midblastula transition’ (4000 – 8000 cells); at this stage transcription is activated and the embryo begins to use the products of its own genes (Newport and Kirschner, 1982). The stored material includes, beside proteins and mRNAs, a huge amount of ribosomes (1012 per oocyte) accumulated as 80S particles, which are sufficient to support protein synthesis for a considerable part of embryogenesis; when they become limited the embryo begins making new ribosomes. We were interested in studying, during this period of development, the regulation of expression of the protein component of the ribosomes, the numerous ribosomal proteins (r-proteins), whose coordinated production implies a fine regulation. A coregulation with ribosomal RNAs, with which they are functionally related, could also be expected.
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