BOVINE OOCYTE DIAMETER IN RELATION TO MATURATIONAL COMPETENCE AND TRANSCRIPTIONAL ACTIVITY

The aims of the present series of experiments were to establish a poss ible relationship between bovine oocyte diameter and follicle size, in vestigate the developmental ability of oocytes of different diameter g roups, and investigate the relationship between oocyte diameter and RN A transcriptional activity of the oocyte. Follicles were recovered fro m slaughterhouse ovaries by mechanical dissection, measured, and assig ned 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 fro m the follicles and their diameters recorded. The correlation coeffici ent between oocyte diameter and follicle size was 0.32 (P < 0.0001). O ocytes were recovered by aspiration and/or slicing of slaughterhouse o varies and divided into four groups ((100 mu m, 100-<110 mu m, 110-(12 0 mu m, and >120 mu m) based on diameter. Oocytes were processed throu gh standard procedures for in vitro maturation and stained in order to assess nuclear development. Rates of in vitro development to metaphas e II were 21.2%, 42.3%, 75.9%, and 80.7%, respectively, for the four g roups. On a separate occasion immature oocytes from the above diameter groups were cultured in the presence of H-3-uridine for 45 min and sc ored for degree of RNA synthesis as indicated by the presence of autor adiographic labeling. Oocytes <110 mu m showed a greater degree of H-3 -uridine incorporation than those greater than or equal to 110 mu m, s uggesting that they were involved in RNA synthesis and therefore still in the growth phase. (C) 1995 Wiley-Liss, Inc.