BOVINE OOCYTE DIAMETER IN RELATION TO MATURATIONAL COMPETENCE AND TRANSCRIPTIONAL ACTIVITY

The aims of the present series of experiments were to establish a possible relationship between bovine oocyte diameter and follicle size, investigate the developmental ability of oocytes of different diameter groups, and investigate the relationship between oocyte diameter and RNA transcriptional activity of the oocyte. Follicles were recovered from slaughterhouse ovaries by mechanical dissection, measured, and assigned to one of the following size categories: greater than or equal to 4 mm, <3-4 mm, (2-3 mm, <1-2 mm, and <1 mm. Oocytes were liberated from the follicles and their diameters recorded. The correlation coefficient between oocyte diameter and follicle size was 0.32 (P < 0.0001). Oocytes were recovered by aspiration and/or slicing of slaughterhouse ovaries and divided into four groups ((100 mu m, 100-<110 mu m, 110-(120 mu m, and >120 mu m) based on diameter. Oocytes were processed through standard procedures for in vitro maturation and stained in order to assess nuclear development. Rates of in vitro development to metaphase II were 21.2%, 42.3%, 75.9%, and 80.7%, respectively, for the four groups. On a separate occasion immature oocytes from the above diameter groups were cultured in the presence of H-3-uridine for 45 min and scored for degree of RNA synthesis as indicated by the presence of autoradiographic labeling. Oocytes <110 mu m showed a greater degree of H-3-uridine incorporation than those greater than or equal to 110 mu m, suggesting that they were involved in RNA synthesis and therefore still in the growth phase. (C) 1995 Wiley-Liss, Inc.