Studies on the promoting effects of cumulus cells on cytoplasmic maturation of bovine immature oocytes during in vitro maturation culture.

点击翻译按钮获取中文摘要

The competence of postfertilization development to blastocysts of bovine oocytes is acquired during in vitro maturation (IVM) period. The developmental competence, referred to as cytoplasmic maturation, is promoted by midkine (MK). MK is a retinoic acid (RA)-inducible and heparin binding growth factor. Recently it was found that apoptosis occurred in cumulus cells of bovine cumulus-enclosed oocytes (CEOs) during IVM, suggesting that the degree of apoptosis in cumulus cells of CEOs may be correlated with their cytoplasmic maturation. The present study was undertaken to examine the effects of MK and RA on cytoplasmic maturation of bovine CEOs and apoptosis of their cumulus cells during IVM period. As a result, it was found that MK and RA had cytoplasmic maturation-promoting activities. Ligation-madiated PCR experiments revealed that the degree of apoptotic internucleosomal DNA fragmentation in cumulus cells of CEOs was significantly lower in MK- or RA-treated CEOs compared to the untreated control group. Next, the effects of carnitine, which has an anti-apoptotic activity to various types of cells, on cytoplasmic maturation of bovine CEOs were examined, because carnitine transporter was detected both in oocytes and cumulus cells of CEOs using immunofluorescence method. It was found that transition of active mitochondria from cortex region into inner cytoplasm as well as cytoplasmic maturation of CEOs were promoted by carnitine treatment during IVM. Finally, suppression subtractive hybridization analysis revealed that expression of some genes such as topoisomerase α, apoptosis related gene and ovary specific gene OVN6-2 in cumulus cells were promoted by MK treatment.