Inhibitor of ribosomal RNA synthesis in Xenopus laevis embryos. I. Changes in activity in activity of the inhibitor during development and its distribution in early gastrulae

Attmepts to analyse the biochemical basis of regional differences in animal eggs

The microinjection of cell material or macromolecules into living cells is potentially useful for identifying cell components responsible for positional information. Experiments with purified globin mRNA injected into frog oocytes and eggs show that macromolecules can retain their activity when injected into living cells. Experiments with histones show that injected macromolecules can take up their normal intracellular location in living cells. Attempts have been made to identify the molecules involved in regulating DNA synthesis, ribosomal RNA synthesis, and early developmental events by fractionating egg cytoplasm, and by rescuing maternal effect mutants. The present state, and theoretical basis, of such experiments is discussed.

Cloning of Xenopus Dr1 (TBP-binding repressor) and its expression in oocytes and early embryos

With a final goal to study how TBP-binding repressor Dr1 regulates transcription in Xenopus early embryos, we cloned its cDNA from Xenopus liver cDNA library. The cDNA was 1,986 bp long, with the open reading frame coding for 175 amino acids, whose sequence was highly homologous to its human counterpart. Xenopus Dr1 mRNA was expressed from the earliest stage of oogenesis, inherited as maternal mRNA at a high level, but its level became low at and after the neurula stage where RNA synthetic activity is strongly activated. Dr1 mRNA occurred in larger amounts in the animal half than in the vegetal half in 8-cell stage embryos, and in neurula and tailbud stage embryos its distribution was slightly larger in the anterior part than in the posterior part. These data show that Dr1 mRNA is expressed in a temporally and spatially regulated manner, and its occurrence at higher levels in earlier stage embryos may be responsible for their low transcriptional activity.