Bovine cumulus-oocyte-complex-quality is reflected in sensitivity for α-amanitin, oocyte-diameter and developmental capacity

The aim of the present study was to find more parameters to define developmental competence of cumulus-oocyte-complexes (COCs). Bovine COCs were divided into five groups based on their morphology. In order of increasing level of atresia: COG-A had a bright, compact cumulus invest ment: COC-B1 also had a compact cumulus investment, but was darker than COG-A; the color of COC-B2. was comparable with COC-B1 but the corona radiata appeared to dissociate from the rest of the cumulus investment; the cumulus of COC-B3 was almost black and the corona radiata was almost completely dissociated from the rest of the cumulus investment; COC-C had a strongly expanded cumulus investment with dark spots of degenerated cells. An increasing level of atresia was accompanied by: (1) an increasing zona pellucida diameter (147.6, 150.8, 151.0, 154.3 and 155.1 mum, respectively, for COG-A, COC-B1, COC-B2, COC-B3 and COC-C); (2) an increasing oocyte diameter except for COC-C (120.9, 122.8, 122.8, 123.9 and 118.4 mum, respectively); (3) an increasing developmental competence except for COC-C (13.9, 14.7, 17.4, 19.1 and 11.5%, respectively, development to morula and blastocyst after in vitro embryo production (IVP)) and (4) by a increasing percentage of oocytes exhibiting germinal vesicle breakdown (GVBD) after 24 h culture with alpha -amanitin and FSH, except for COG-A (34.4, 68.6, 51.0, 22.0 and 4.8%, respectively, oocytes arrested in GV). In general. embryo-quality, expressed in nuclei-count, was significantly affected by COG-quality (P < 0.05) with B3 > B1 > B2 > A > C. However, if the developmental stages were compared separately, this effect was less evident. It was found that, in absence of FSH, a-amanitin was unable to inhibit GVBD and that the success of GVBD inhibition was positively correlated to the amount of cumulus cells surrounding the oocyte. COCs that had been exposed to alpha -amanitin and FSH during maturation retained the ability to cleave after IVE but were unable to develop any further. (C) 2001 Elsevier Science B.V. All rights reserved.