Cytochalasin D treatment induces meiotic resumption in follicular sheep oocytes

Abstract

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.

Co‐Expression of Cytokeratins and Vimentin in Sheep Cumulus‐Oocyte Complexes. Alteration of Intermediate Filament Distribution by Acrylamide

“…The loss of gap junctions as a consequence of the foot process retraction suggests an important remodelling of cytoskeletal elements. De Smedt and Szollosi (5) demonstrated that COCs of sheep treated with cytochalasin, a cytoskeletal disrupting agent which disturbs the actin network in the foot processes, leads to the isolation of the oocyte from its surrounding cells and results in high rates of maturation (5). Similar result were reported for the rat by Dekel et al (6).…”

Control of Oocyte Growth and Development by Intercellular Communication Within the Follicular Niche

“…TZPs link the surrounding follicle cells to the oocyte in most, and possibly all, mammalian species (Anderson and Albertini 1976;Hertig and Adams 1967), and similar structures have been observed in numerous nonmammalian species (Kessel et al 1985;Schroeder 1981). Most TZPs contain an actin backbone, but a small fraction contains microtubules instead (Albertini and Rider 1994;De Smedt and Szollosi 1991). At the tips of the TZPs, where they contact the oocyte plasma membrane, are located gap junctions (which may also link TZPs to each other) (Anderson and Albertini 1976;Albertini and Rider 1994).…”

Cytokeratin dynamics during oocyte maturation in the hamster requires reaching of metaphase I

“…This finding may relate to perturbation of cumulus cell-oocyte interactions [17,55]. First, incubation of COC with nocodazole led to a metaphase I-like arrest, which is to be expected.…”