THECA CELLS AND THECA-CELL CONDITIONED MEDIUM INHIBIT THE PROGRESSIONOF FSH-INDUCED MEIOSIS OF BOVINE OOCYTES SURROUNDED BY CUMULUS CELLS CONNECTED TO MEMBRANA GRANULOSA

The effect of follicular cells and their conditioned media on the FSH- induced oocyte maturation of oocytes surrounded by cumulus cells conne cted to the membrana granulosa (COCGs) was investigated. COCGs and cum ulus oocyte complexes (COCs) were cultured for 22 hr in M199 supplemen ted with 0.05 IU FSH/ml in either the presence of pieces of theca cell layer or in the presence of pieces of membrana granulosa. COCGs and C OCs were also cultured for 22 hr in either theca-cell conditioned medi um (CMt) or in granulosa cell conditioned medium (CMg), both supplemen ted with 0.05 IU FSH/ml. To investigate the importance of cell-cell co ntacts between granulosa cells and cumulus cells, oocytes were culture d as COCs in CMt, as COCs in CMt supplemented with pieces of membrana granulosa, or as COCGs in CMt. In all groups the medium was supplement ed with 0.05 IU FSH/ml. After culture the nuclear status of the oocyte s was assessed using orcein staining. Culture of COCGs in the presence of theca cells as well as in CMt resulted in a significantly decrease d proportion of oocytes that had undergone germinal vesicle breakdown (GVBD) at the end of the culture period as compared to the control. Of the oocytes that resumed meiosis in the presence of theca cells or in CMt, the proportion of oocytes that progressed up to the MII stage wa s significantly reduced. This indicates the production of a meiosis-in hibiting factor by theca cells. Culture with COCs instead of COCGs res ulted in comparable results although the effect was less pronounced. T he significant effect on the progression of meiosis of oocytes culture d as COCGs or as COCs, obtained in the presence of granulosa cells or in CMg, was much weaker than the effect of theca cells or culture in C Mt. Culture of COCs in CMt supplemented with layers of membrana granul osa and 0.05 IU FSH/ml, resulted in significantly less oocytes that re sumed meiosis as compared to culture of COCs in CMt, Of the oocytes th at showed GVBD, the proportion that progressed up to the MII stage was significantly reduced. Attachment of the COCs to the membrana granulo sa enhanced this inhibiting action of CMt on the progression of meiosi s. It is concluded that theca cells secrete a stable factor that inhib its the progression of FSH-mediated meiosis in oocytes of COCGs. (C) 1 998 Wiley-Liss, Inc.