Cytochalasin D treatment induces meiotic resumption in follicular sheep oocytes.
Ovine cumulus-enclosed oocytes collected from antral follicles (3-5 mm in diameter) were cultured in vitro with 2 x 10(6) granulosa cells/ml in the presence or absence of gonadotropins or in the presence of cytochalasin D (CD). The maturation rate was assessed after 24 h of culture. In the control group, in the presence of gonadotropins (follicle-stimulating hormone-luteinizing hormone (FSH-LH; -10 micrograms/ml) 100% of the oocytes reached metaphase II. Whereas intercellular junctions were no longer present after 6-7 h of culture, germinal vesicle breakdown (GVBD) occurred by the same time. In contrast, in the absence of gonadotropin, the majority of the oocytes (59%) remained blocked in GV stage. The inhibition exerted by the granulosa cells on meiotic resumption was overcome when the cumulus-oocyte complexes (COCs) were incubated in CD (5 micrograms/ml) for 6 h at the beginning of the culture. Under these conditions, 85% of the oocytes matured with extrusion of the first polar body. Cytological analysis by cytofluorescence (NBD phallacidin) and electron microscopy showed that, after 6 h of treatment, CD provoked a redistribution of the microfilaments, mainly in the cumulus cells and to a lesser extent in the oocyte cortex. Intercellular junctions disappeared concomitantly with a significant decrease of the intercellular transport of tritiated uridine. The initiation of GVBD occurred at the same time. These results indicate that the resumption of meiosis was correlated with a loss of both junctional complexes (intermediate and gap junctions) between the cumulus cells and the oocyte.
De Smedt
V
V
I.N.R.A., Unité de Biologie de la Fécondation, Jouy-en-Josas, France.
Szöllösi
D
D
D000818:Animals; D015638:Cytochalasin D / Q000494:pharmacology*; D005260:Female; D005455:Fluorescent Antibody Technique; D005640:Follicle Stimulating Hormone / Q000494:pharmacology; D006107:Granulosa Cells / Q000502:physiology; D007365:Intercellular Junctions / Q000648:ultrastructure; D007986:Luteinizing Hormone / Q000494:pharmacology; D008540:Meiosis; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D009865:Oocytes / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D012756:Sheep; D014415:Tunicamycin / Q000494:pharmacology
D014415:Tunicamycin; D015638:Cytochalasin D; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone