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(189) ROLE OF FAS-MEDIATED APOPTOSIS AND FSH ON THE DEVELOPMENTAL CAPACITY OF BOVINE CUMULUS OOCYTE COMPLEXES IN VITRO. Rubio-Pomar, Francisco1, Roelen, Bernard 1, Slot, Karin2, vanTol, Helena1, Colenbrander, Ben1, Teerds, Katja3, 1 Department of Farm Animal Health, Utrecht, The Netherlands2 Department of Cell Biology and Biochemistry, Utrecht, The Netherlands3 Department of Animal Sciences, Wageningen, The Netherlands ABSTRACT- In the ovary, follicular atresia is thought to be largely regulated by apoptosis. One of the mechanisms involved in the regulation of follicular programmed cell death is the activation of the Fas signaling pathway. To further understand how apoptosis can affect cumulus cells and oocytes we have evaluated the expression of components of the Fas signaling pathway in bovine oocytes and cumulus cells. Furthermore, this signaling pathway was activated in cumulus oocyte complexes (COCs) with an agonistic anti-Fas antibody during in vitro maturation in the presence or absence of FSH. After maturation, viability and incidence of apoptosis in cumulus cells were evaluated by assessing membrane integrity and nuclear morphology. Oocyte nuclear maturation was also analyzed, as well as cleavage rates, blastocyst formation rates and blastocyst quality, following in vitro fertilization. Fas mRNA and protein were detected both in oocytes and cumulus cells. FasL protein was found in cumulus cells but could not be detected in oocytes, despite its mRNA expression. An increase in the incidence of apoptosis in cumulus cells was observed when COCs were cultured in the presence of the agonistic anti-Fas antibody (21%) or FSH (16%) compared to control COCs matured in M199 (3%). This increase affected predominantly the peripheral region of the cumulus. No effect was observed on nuclear maturation of oocytes neither on cleavage and blastocyst formation rates after IVF due to activation of the Fas pathway. Presence of FSH during culture improved oocyte developmental potential in blastocyst formation rates. No differences in quality were observed among the obtained blastocyst from oocytes matured in the presence of the Fas activating antibody and/or FSH. In conclusion, apoptosis in bovine cumulus cells during IVM can be induced via activation of the Fas signaling pathway, a pathway which is not functional in oocytes. Moderate apoptosis in cumulus cells during IVM as induced by Fas signaling or FSH does not severely affect the corona radiata cells and has no evident unfavorable effect on the developmental potential of the oocyte. KEY WORDS: Cumulus, Blastocysts, Apoptosis, Oocytes |
