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ARS Home » Research » Publications at this Location » Publication #107443
Title: CHANGES IN PORCINE OOCYTE GERMINAL VESICLE DEVELOPMENT DURING FOLLICLE MATURATION

Author
item Guthrie, Howard
item GARRETT, WESLEY - 1265-10

Submitted to: Journal of Molecular Reproduction and Development
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/4/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: During the three day period of the reproductive cycle when follicles are selected to ovulate in the pig, only 20% present on the ovaries at that time survive and are selected to ovulate. The rational for the production of so many germ cells during early fetal life and their subsequent loss in pigs and other species is unknown. On explanation may be that functional life span of the mature, fully grown oocyte becomes much shorter after antrum formation. At most times before follicle numbers have been reduced prior to ovulation up to 70% of oocytes have resumed meiotic maturation prematurely. Therefore, apoptosis and follicle atresia may be required to eliminate oocytes that no longer developmentally competent even if they are fertilized. Additional research to define the functional lifespan of the oocyte and its relationship to follicle growth and atresia may reveal methods to generate more developmentally competent oocytes and increase reproductive efficiency in swine.

Technical Abstract: Porcine embryo production in vitro is very inefficient, with at best a 20% yield of blastocyts. A factor that may effect embryo production is the maturational status of oocytes before culture. Recent studies have shown that GV development in oocytes isolated from prepuberal gilts ranges from immature to complete breakdown (GVBD). This study was conducted to determine GV development in oocytes recovered from gilts on days 1, 3, 5, and 7 of follicle maturation induced by withdrawal of altrenogest treatment. Oocytes were stripped of cumulus cells in 0.1% hyaluronidase, fixed in 4% paraformaldehyde, stained with Hoechst 33342, and analyzed by confocal microscopy using combined bright field Nomarski optics and ultraviolet laser illumination. The percentages of oocytes from nonatretic follicles in stages GV-I, GV-II, GV-III/IV, and GVBD on days 1, 3, 5, and 7, respectively, were 29, 47, 24, and 0 (n=17); 79, 18, 3, and 0 (n=28); 67, 30, 3, and 0 (n=36); and 18, 13, 5, and 64 (n=39). GV distributions on days 1 and 7 differed from each other and from those on days 3 and 5. The distribution of GV stages did not differ between atretic and nonatretic follicles. GV stages were assigned a numeric score, 1, 2, 3, and 4 for correlation analysis with follicular fluid steroid levels. In nonatretic follicles on days 5 and 7 (not days 1 and 3), GV score was inversely related to concentrations of estradiol, progesterone and androstenedione indicating that immature oocytes were more likely found in follicles with highest levels of steroidogenesis. In conclusion, a large proportion of oocytes present on day 1 had begun GVBD which could have a negative impact if they were used for embryo production in vitro. A physiological mechanism may exist to select follicles for maturation that are primarily nonatretic.