Effect of maternal age on the developmental competence and progression of nuclear maturation in bovine oocytes.

Progression of meiotic division in oocytes and early embryonic development are affected by oocytes quality. In most mammals, oocyte quality declines with increase in maternal age. The main aim of the present study is to investigate the effect of maternal age on developmental competence, progression of meiotic division, and associated kinetics of maturation promoting factor (MPF) activity in bovine oocytes. Oocytes were collected from the ovaries of young and old cows (here after referred to as young cow oocytes and old cow oocytes, respectively). When old cow oocytes were matured and fertilized in vitro, the rate of abnormal fertilization was greater than that in young cow oocytes. Moreover, progression of nuclear maturation and activation of MPF during oocyte maturation (or inactivation of MPF and formation of pronucleus after insemination) were faster in old cow oocytes than in young cow oocytes. Relative expression of cyclin B, cyclin-dependent kinase 1 and MAD2 transcripts in either immature or mature oocytes did not differ between the two groups. When cumulus cells (CC) were removed and denuded oocytes were cultured, there was no difference in the progression of nuclear maturation between the two age groups. Moreover gap junctions between oocytes and CC disappeared more rapidly during maturation of old cow oocytes than of young cow oocytes. These results suggest that the fertilization ability of old cow oocytes is low and that premature progression of meiotic division in these oocytes is partly due to impaired oocyte-CC gap junctions communication. (c) 2010 Wiley-Liss, Inc.