MPF-induced breakdown of cytokeratin filament organization in the maturing Xenopus oocyte depends upon the translation of maternal mRNAs.

In Xenopus, one of the most dramatic events during oocyte maturation is the breakdown of the oocyte's asymmetrically organized system of cytokeratin-type intermediate filaments. Following oocyte maturation in vitro, we found that (1) the breakdown of cytokeratin filament organization proceeds in an animal to vegetal direction, (2) cytokeratin filament breakdown occurs normally in enucleated oocytes and so is independent of nuclear components, and (3) the injection of maturation-promoting factor (MPF) induces the breakdown of cytokeratin filaments. While the MPF-induced breakdown of the nuclear envelope is independent of new protein synthesis, the MPF-induced breakdown of cytokeratin filament organization requires the translation of maternal mRNAs. These results strongly suggest that the factors regulating cytokeratin reorganization in the oocyte are distinct from those involved in the breakdown of the nuclear envelope.