A role for transcription and FRGY2 in masking maternal mRNA within Xenopus oocytes.

We find that mRNA synthesized within the Xenopus oocyte nucleus is translated with an efficiency 50 times less than that of mRNA injected into the oocyte cytoplasm. For histone H1 mRNA this effect is independent of mRNA splicing, nuclear export, and the promoter driving transcription. The mRNA synthesized in vivo is translationally competent but is masked from the translational machinery in the cytoplasm through association with proteins including frog Y-box protein 2 (FRGY2). We find that overexpression of FRGY2 facilitates the translational repression of mRNA synthesized within Xenopus oocytes. The requirement for transcription to occur in vivo before a translationally repressed state can be established suggests that these two events are functionally coupled in Xenopus oocytes.