Effect of follicular components on meiotic arrest and resumption in horse oocytes

Abstract

Two experiments were conducted to evaluate the effect of follicular components on the maintenance of meiotic arrest in horse oocytes. In Expt 1, oocytes were incubated for 24 h with follicular fluid, or with granulosa cells suspended either in medium or in follicular fluid at 25 x 10(6) cells ml-1. None of the treatments resulted in significant maintenance of the germinal vesicle stage over that of non-suppressive control. Culture with follicular fluid plus granulosa cells resulted in a significantly higher proportion of oocytes at metaphase I compared with controls. In Expt 2, oocytes were divided into those originally having compact or expanded cumuli. Oocytes were cultured with sheets of mural granulosa or sections of follicle wall, or after injection into intact dissected follicles. After incubation, half of the oocytes from each suppressive treatment were matured for 24 h. All three suppressive treatments were effective in maintaining oocytes at the germinal vesicle stage (no significant difference from control oocytes fixed directly after removal from the follicle). However, no treatment maintained normal viability of oocytes, as significantly fewer oocytes were at metaphase II after all the suppression-maturation treatments compared with the maturation control. The highest rate of post-suppression maturation was found in the mural granulosa treatment. Within this treatment, the proportion of oocytes in metaphase II was significantly higher for oocytes with expanded than for oocytes with compact cumuli (31% versus 11%, respectively; P < 0.05). Suppression by injection into an intact follicle was associated with a lack of progression to metaphase II during subsequent maturation.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationships among Oocyte-Cumulus Morphology, Follicular Atresia, Initial Chromatin Configuration, and Oocyte Meiotic Competence in the Horse1

“…EX and CP horse oocytes have similar proportions at the germinal vesicle stage at the time of removal from the follicle (73% and 78%, respectively [4]). Germinal vesicle-stage EX and CP oocytes are both capable of being kept in meiotic suppression by coculture with follicular components [10] or treatment with cycloheximide [11], indicating that they are not committed to mature at the time they are recovered from the follicle. EX horse oocytes mature to metaphase II in vitro in proportions equal to or greater than those for CP oocytes [4,[10][11][12][13][14][15].…”

“…Germinal vesicle-stage EX and CP oocytes are both capable of being kept in meiotic suppression by coculture with follicular components [10] or treatment with cycloheximide [11], indicating that they are not committed to mature at the time they are recovered from the follicle. EX horse oocytes mature to metaphase II in vitro in proportions equal to or greater than those for CP oocytes [4,[10][11][12][13][14][15]. After being released from meiotic suppression with cycloheximide or follicular components, more EX than CP oocytes are capable of maturation [10,11].…”

“…EX horse oocytes mature to metaphase II in vitro in proportions equal to or greater than those for CP oocytes [4,[10][11][12][13][14][15]. After being released from meiotic suppression with cycloheximide or follicular components, more EX than CP oocytes are capable of maturation [10,11]. EX oocytes mature more quickly in vitro than do CP oocytes [4,12], and the period of protein synthesis needed for resumption of meiosis is shorter for EX than for CP oocytes [11].…”

Comparative Evaluation of Nuclear Morphology of Equine Oocytes Aspirated in vivo and Stained with Hoechst and Orcein

“…Thus, the incidence of germinal vesicle (GV) stages has been reported to be between 3 and 80%; the incidence of resumption of meiosis, i.e. germinal vesicle breakdown (GVBD) up to metaphase I (MI) stages between 3 and 55% and the incidence of metaphase II (MII) stages between 0 and 13% [Desjardins et al, 1985;Okolski et al, 1991;Willis et al, 1991Willis et al, , 1994Bézard and Palmer, 1992;Hinrichs et al, 1993aHinrichs et al, , 1995Alm and Torner, 1994;Del Campo et al, 1995;Torner and Alm, 1995;Brück et al, 1996Brück et al, , 1997.…”

“…The time of transport has been reported between 2.5 and 6 h [Alm and Torner, 1994;Willis et al, 1994;Brück et al, 1996] and the time interval between collection and fixation is generally longer for oocytes after slaughter than after collection by in vivo follicular aspiration. It is known that equine COCs removed from follicles resume meiosis after 8 and 16 h of culture [Hinrichs et al, 1993a], and it has been suggested that resumption of meiosis is prevented by a soluble mediator which is transmitted via gap junctions between mural granulosa cells, cumulus cells and oocyte [Hinrichs et al, 1995;Yding Andersen et al, 1999]. If the COCs, on the other hand, are left in the ovaries during transport, these cell connections are also likely to disintegrate over time.…”