Destruction of a translationally controlled mRNA in Xenopus oocytes delays progesterone-induced maturation

Abstract

The maternal mRNA D7 is a moderately abundant transcript in Xenopus laevis whose expression is highest in, and perhaps restricted to, oogenesis and early embryogenesis. The nucleotide sequence of cloned D7 cDNA was determined and shown to have the capacity to code for a 31-kD protein. This amino acid sequence was searched against a protein data base, and no homologous proteins were found. Antibodies directed against D7 recognize in Xenopus embryos a soluble, cytoplasmic protein with an apparent molecular weight on SDS gels of 36,000. The D7 protein is absent from oocytes and first begins to accumulate during oocyte maturation. Its levels are highest during the first day of embryonic development and then decrease; D7 protein was not detected in adult tissues. D7 mRNA was selectively destroyed by injection into oocytes of antisense oligodeoxynucleotides. Analysis of injected oocytes by Northern and Western blotting showed site-specific cleavage and subsequent degradation of the D7 mRNA and the failure of the D7 protein to accumulate during progesterone-induced maturation. The loss of D7 protein affects the maturation process itself, significantly delaying the time course of germinal vesicle breakdown. Thus, D7 is a newly described protein involved in oocyte maturation.