OOCYTE GROWTH, CAPACITATION AND FINAL MATURATION IN CATTLE

The oocyte growth phase includes a series of modulations of organelles and inclusions, as well as a period of oocyte transcription, which ar e necessary for the oocyte to achieve meiotic and developmental compet ence. Oocyte transcription including nucleolar function (rRNA-synthesi s) is activated in the secondary follicle and is maintained up to an o ocyte diameter of about 110 mu m in the 3 mm tertiary follicle. At a d iameter of 100 to 110 mu m, the oocyte gradually achieves the competen ce to undergo meiotic maturation and sustain embryonic development. In the dominant follicle the oocyte undergoes further ultrastructural mo difications and attains full developmental competence through a proces s that may be termed ''capacitation''. The final oocyte maturation up to metaphase II after LH stimulation of the ovulatory follicle is the culmination of the previous processes and equips the oocyte with a hap loid chromosomal compartment and the cell biological apparatus special ized for fertilization and initial embryonic development. (C) 1996 by Elsevier Science Inc.