RNA synthesis in fully-grown mouse oocytes

IT is now well documented for various species that the progress of early development depends to a large extent on materials synthesised and stored in the oocyte during oogenesis. A well studied example of this phenomenon is the synthesis and accumulation of both ribosomal and "informational" RNA in amphibian oocytes^1-3. The extent of the contribution of oocyte RNA to early mammalian development is, however, not completely clear, since mouse embryos initiate rRNA synthesis at least as early as the four-cell stage of embryogenesis^4,5 and, unlike certain lower forms, the progress of early cleavage in the mouse is interfered with by inhibitors of RNA synthesis^6-8. On the other hand, it is clear that growing mouse oocytes synthesise and store RNA^9-12, such that the ovulated egg contains approximately the same amount of RNA on a volume basis as the amphibian egg (calculated from refs 13 and 14).