Functional enucleation of bovine oocytes: effects of centrifugation and ultraviolet light

Functional enucleation is removal or denaturation of an oocytes DNA without piercing the zona pellucida. Two experiments were conducted in this study to determine the effects of centrifugation, and ultraviolet (UV) light on metaphase II bovine oocytes. Experiment 1 evaluated the effects of centrifugation (12,000 x g for 4 min) on the cleavage rate of in vitro matured oocytes. Centrifugation decreased (P < 0.05) the cleavage rate of oocytes (79.5 vs 70.4%). In addition, it was noted that there were two types of ooplasm after centrifugation, stratified and granular. Developmental potential, as represented by cleavage percent, of the two types of ooplasm was not significantly different. Experiment 2 was conducted to determine the interactive effects of centrifugation (as above) and UV light (254 nm) on cleavage rate of oocytes exposed as metaphase II oocytes. The UV light decreased (P < 0.07) oocyte cleavage rates (35.4 vs 25.2%). Centrifuging metaphase II oocytes also decreased (P < 0.07) cleavage rates (34.1 vs 26.5%). In addition, we determined the fate of chromosomes of oocytes centrifuged and(or) exposed to UV light. Both centrifugation and UV light alone affected (P < 0.05) chromosome placement at 42 +/- 3 h after fertilization. Furthermore, centrifugation and UV light interactively increased (P < 0.05) the percentage of non-cleaved oocytes with their DNA located in the perivitelline space (17.4, 15.5, 13.1, and 49.2, respectively, for control, UV exposed, centrifuged, and UV *centrifuged). Collectively, these data indicate that bovine oocytes at the metaphase II stage can be functionally enucleated with centrifugation and exposure to UV light; however, developmental potential may be diminished by those techniques.