Masking and Unmasking Maternal mRNA

Abstract

We establish that masked mRNAs synthesized from exogenous plasmid templates microinjected into the nu-clei of Xenopus oocytes are translationally activated (unmasked) on oocyte maturation concomitant with pol-yadenylation. Synthetic mRNA injected into the cyto-plasm of the oocyte is translated over an order of magnitude more efficiently than is the cognate mRNA synthesized in vivo. Both mRNA synthesized in vivo and mRNA microinjected into the oocyte cytoplasm require a cytoplasmic polyadenylation element in the 3-un-translated region to activate translation on maturation. Although polyadenylation upon oocyte maturation can relieve the translational repression of mRNA synthesized in vivo, the excision of an intron within the nucleus does not relieve repression. We suggest that the translational repression coupled to the transcription process will more effectively repress inappropriate gene expression in the oocyte and offer the potential to achieve a wider range of gene regulation.