Effects of follicular phase and oocyte-cumulus complexes quality on the protein profile and in vitro oocyte meiosis competence in Cebus apella

Abstract

Objective: To study the protein profile of oocytes and cumulus cells from different sized follicles throughout the follicular phase and to asses the ability of oocytes to progress from the dictyate to metaphase II (MII) stage.

Design: Animal model study.

Setting: Five academic basic research laboratories and the National Primate Centre.

Animal(s): Eleven normal, cycling capuchin monkey (Cebus apella) females.

Intervention(s): Cumulus-oocyte complexes and denuded oocytes were recovered by antral follicle aspiration.

Main outcome measure(s): Protein profile analysis of denuded or intact oocytes.

Result(s): The protein profiles of 25 denuded or intact oocytes recovered on days 5 (six denuded, five intact), 7 (four denuded, four intact), or 9 (one denuded, five intact) of the menstrual cycle were analyzed; in a second experiment, 40 intact oocytes were cultured for 24 (n = 20) or 36 hours (n = 20). The oocytes were denuded, fixed, stained, and microscopically examined to reveal the meiotic stage. The protein profile in each compartment within the cumulus-oocyte complex varied along the follicular development with a predominance of low-molecular-weight proteins in both oocyte and cumulus cells at final stages. No differences were found in the protein profile among oocytes pertaining to different sized follicles that were in the same day of the follicular phase. Oocyte MII competence was achieved only after incubation for 36 hours, and the highest maturation rate occurred in those becoming from dominant follicles.

Conclusion(s): Our study shows, for the first time in a New World primate species, that the proteins contained in oocytes and cumulus cells reach an identical profile in the late follicular phase. This phenomenon could be related to the oocyte's ability to progress to the MII stage.