Effects of Oxygen Tension on Survival and Growth In Vitro of Bovine Oocytes from Early Antral Follicles

Abstract

The purpose of this study was to assess the effect of oxygen condition on the survival and growth in v it ro of b ovi ne o ocy te -c umu lus /g ra nu los a ce ll co mplexes isolat ed fro m ear ly a ntr al f ollicl es. Complexes comprised of a growing oocyte enclosed inPrimordial follicles in mammalian ovaries are a large source of oocytes, though most of them undergo degeneration before recruitment in the growing pool. These primordial follicles would be a potentially valuable resource, if we could rescue them before they are lost in ovaries and if we could provide them with environments that will support their growth and differentiation to a growth stage equivalent to that of oocytes in preovulatory follicles, but it is very difficult to utilize them with the current culture technology, though it is not impossible [1]. A more applicable approach may be culturing of oocytes that have already entered the growing phase, because most them will degenerate in ovaries before completion of the lengthy process of growth to the final size. Various culture systems have been devised for growing oocytes in several species, including mice, rats, pigs, cattle, sheep and humans; see [2] for reviews. Among these studies, several different culture systems have been tested for mouse oocytes, and it has become evident that mouse oocytes can be fully-grown in vitro from the mid-growth phase at a moderate frequency, and achieve the competence to undergo meiotic maturation and fertilization [3][4][5]. S o m e o f t h e m a r e c o m p e t e n t t o u n d e r g o preimplantation embryo development, and even further development [1,3,5]. Except for studies on the mouse, most well established culture systems are probably

Optimization of Oxygen Concentration for Growing Bovine Oocytes <i>In Vitro</i>: Constant Low and High Oxygen Concentrations Compromise the Yield of Fully Grown Oocytes

“…However, the resulting oocytes are on average smaller than those grown in follicles in vivo. Further improvement of the culture system is therefore necessary.Our previous work comparing bovine oocyte growth in reduced (5%) and ambient (20%) oxygen concentrations [2] suggests the importance of oxygen optimization in determining culture conditions. The oxygen environment has significant effects on cell activities in culture in various cell types, such as somatic cells [3,4], embryos [5,6] and stem cells [7].…”