MEIOTIC MATURATION IN CULTURED BOVINE OOCYTES IS ACCOMPANIED BY REMODELING OF THE CUMULUS CELL CYTOSKELETON

Mammalian oocyte maturation and cumulus expansion are hormone-induced contemporaneous processes that involve changes in cumulus cell shape and in the interactions between cumulus cells and the oocyte. Laser scanning confocal and conventional fluorescence microscopy have been used to study the relationship between reorganization of the cumulus cell cytoskeleton and meiotic progression in bovine cumulus oocyte complexes (COCs) matured in vitro. Inclusion of hormone supplements (FSH, LH, E2) in the maturation media was required for meiotic progression to metaphase 2 and maximal cumulus expansion. Under these conditions, stage-specific changes in the cytoskeletal content and organization of cumulus cell transzonal processes was observed. Specifically, abundant, actin-filled transzonal processes were observed in GV stage COCs. In stages intermediate in the maturation process (10 hr culture), fewer actin-filled transzonal processes were seen and microtubule-filled transzonal processes became apparent. At the end of maturation (24 hr culture), numerous, elongate microtubule rich transzonal processes were evident and actin-filled processes were rarely observed. Additionally, a spatial relationship between microtubule rich transzonal processes and oocyte chromatin was consistently observed in all stages of oocytes examined. These results indicate that bovine oocyte maturation in culture involves modifications of the cumulus cell cytoskeleton that may regulate the onset, progression, and completion of oocyte maturation. © 1993 Academic Press, Inc. © 1993 by Academic Press, Inc.