STRUCTURAL AND FUNCTIONAL-CHANGES IN PORCINE CUMULUS-OOCYTE-COMPLEXESDURING PREOVULATORY MATURATION

According to first results on endoscopical ovum pick up in gilts depen ding on day of estrous cycle, the aim of our investigation was to dete rmine the influence of the stage of preovulatory maturation in relatio n to the hCG stimulated LH peak on the morphology of cumulus-oocyte-co mplexes (COCs) and its influence on the meiotic configuration of oocyt es. Furthermore the distribution of active and repressed mRNAs in pig oocytes and cumulus cells depending on stage of preovulatory maturatio n in vivo were analysed. A total of 45 crossbred Landrace gilts were s ynchronized for 15 days by Regumate(R) and 1000 IU PMSG. The endogenou s LH peak was simulated by the injection of 500 IU hCG 80 hrs after PM SG. Endoscopic oocyte recovery was carried out 2 h before and 10, 22 a nd 34 h after the injection of hCG, respectively. Altogether 461 COCs were aspirated and morphologically classified: 251 COCs for cytologica l investigation and 189 COCs for mRNA-analysis. The cumulus morphology of COC populations recovered 2 h before and 10 h after the injection of hCG was very heterogenous. During this time, most of the COCs (80 t o 77 %, p<0.01) showed a compact or slightly expanded cumulus. Startin g at about 22 h after the injection of hCG, the COC morphology changed drastic: 92.7 % of COC with expanded cumulus, and 34 h after the inje ction of hCG, 92.2 % of the COC expressed only expanded cumulus (p<0.0 1). The percentage of oocytes with a mature meiotic configuration incr eased (11.1; 7.1; 41.4 and 70.2 % respectively, n=238 oocytes, p<0.01) according to the level of preovulatory maturation (-2, 10, 22, 34 h a fter the injection of hCG). The meiotic configuration depended on the COC morphology: compact COCs (88.9 % Diplotene), expanded COCs (53.8 % Metaphase 2) and denuded oocytes (69.2 % degenerated chromatin). The results concerning the distribution of active and repressed mRNAs in c umulus cells and oocytes indicate that at late preovulatory stages of development cumulus cells contain translationally active mRNAs while r epressed mRNAs hardly could be detected. In contrast, oocytes show a d istinct distribution of polysomal and free mRNAs. Until now we can not ice that the active mRNA-pool decreased during maturation. That means at late stages of maturation the majority of mRNAs persists in a repre ssed form. In comparison with the results of morphologically changes o f COCs we conclude that the process of oocyte maturation which was att ended by cumulus cell expansion followed by meiotic nuclear maturation is also characterized by differential activation or repression of mRN As. There is a strong relation between COC morphology, meiotic configu ration, mRNA quality and the preovulatory follicle maturation after ap plication of hCG.