Intermediate filament distribution patterns in maturing mouse oocytes and cumulus cells

Successful oogenesis requires coordinated cytoskeletal rearrangements. While microfilaments and microtubules in mammalian oocytes are well studied, data about intermediate filaments are still scarce and controversial. We investigated intracellular distribution of vimentin and a set of cytokeratins in mouse oocytes and cumulus-oocyte complexes at different maturation stages using immunofluorescence and laser scanning confocal microscopy. Our results showed that conventional cytokeratins and vimentin are present and co-localize in mouse oocytes in the cortex as well as associated with the nucleus, meiotic spindle and meiotic chromosomes. During oogenesis, these intermediate filaments reorganize, moving from the cell periphery to the metaphase plate. Their distribution overlaps with that of fibrillar actin, except that actin does not associate with metaphase chromosomes. The same cytoskeletal proteins are present in cumulus cells and particularly in their trans-zonal projections. In foot processes, they localize in the periphery. The observed intermediate filament distribution patterns suggest transition to a more dynamic state of the cytoskeleton and a possible role in chromatin reorganization after germinal vesicle breakdown. The peripheral position in foot processes presumably allows oocyte-cumulus communications while providing adequate mechanical support.