Evidence for a nuclear factor involved in c-myc RNA degradation during axolotl oocyte maturation.

We have previously described an in vivo heterologous system which has allowed us to study the stability of different Xenopus c-myc RNA constructs injected into axolotl oocytes. In full-grown oocytes, degradation of c-myc RNA does not occur. In mature oocytes treated with progesterone, transcripts containing the coding sequence of the gene are degraded, whereas those corresponding to the 3'UTR (untranslated region) alone are stable. In order to study the role of nuclear or cytoplasmic components in this process, degradation of injected c-myc transcripts was analysed (i) after inhibition of germinal vesicle breakdown (GVBD) in progesterone treated oocytes (ii) after induced maturation of enucleated oocytes, (iii) injection of nuclear contents into immature oocytes and (iv) after direct injection into the germinal vesicle of full-grown oocytes. Our results demonstrate the role of a nuclear factor stockpiled in the germinal vesicle of full-grown oocytes and specifically involved in the degradation of c-myc transcripts containing the coding region. Further biochemical characterization of this new nuclear component should lead to a better understanding of the post-transcriptional control of c-myc expression during oogenesis and early development.