MICROFILAMENTS, MICROTUBULES AND INTERMEDIATE FILAMENTS FULFILL DIFFERENTIAL ROLES DURING GONADOTROPIN-INDUCED EXPANSION OF BOVINE CUMULUS-OOPHORUS

The relationship between cytoskeleton and morphology of cumulus granul osa cells in expanding bovine oocyte-cumulus complexes (OCCs) cultured in vitro has been investigated by the means of indirect immunofluores cence and transmission electron microscopy. The round-shaped cells in unstimulated control OCCs displayed a homogeneous distribution of cyto skeletal networks and cytoplasmic organelles. Luteinizing hormone (LH) stimulation caused the redistribution of microfilaments (MFs), accele rated the development of Golgi apparatus, and led to the generation of lipid droplets in cumulus cells. These changes culminated in the elon gation and polarization of cumulus cells and in the extension of the c ytoplasmic networks of microtubules (MTs) and intermediate filaments ( Ifs) into the newly formed cytoplasmic projections. The culture of OCC s in the presence of microfilament disrupter cytochalasin B prevented cumulus expansion, formation of cellular projections and cell elongati on and suppressed the development of the Golgi apparatus. On the contr ary, cytochalasin had no effect on the abundance and distribution of l ipid droplets and on the integrity of Ifs and MTs. The present data su pport the hypothesis that the response of cumulus granulosa cells to L H is partially mediated by F-actin.