Germinal vesicle configurations and patterns of polypeptide synthesis of porcine oocytes from antral follicles of different size, as related to their competency for spontaneous maturation

Abstract

The cytogenetic configurations of germinal vesicle (gv) chromatin were analyzed for pools of porcine oocytes harvested from small (1.0-2.0 mm), medium (3.0-5.0 mm), and large (6.0-10.0 mm) antral follicles. Groups of oocytes from these follicular classes also were examined by high-resolution, two-dimensional, polyacrylamide gel electrophoresis to compare their patterns of polypeptide synthesis. The results show a high incidence of gross and cytogenetic degeneration among oocytes from small antral follicles as compared with those from medium or lage follicles. Pools of oocytes could be separated, on the basis of gross morphology and integrity of adherent granulosa cells, into two classes: "Type A" which appeared normal, and "type B" which appeared to be atretic. Among selected "type A" oocytes a particular chromatin configuration, termed "fibrous" characterizes the gv of oocytes from small follicles; whereas a different configuration, termed "diffuse," characterizes the gv of oocytes from large follicles. The patterns of polypeptide synthesis were markedly different for samples of "type A" oocytes of the three follicular classes; and the patterns for oocytes from medium and large follicles were more similar to each other than to patterns for oocytes from slall follicles. The incidences of maturational development beyond the gv stage in vitro were similar for "type A" oocytes from the three follicular classes (i.e., 66% to 82% maturation); although "type B" oocytes underwent maturation beyond the gv at a significantly reduced incidence (i.e., 20% to 29% maturation). "Type A" oocytes from large follicles completed maturation in vitro (i.e., underwent the first meiotic division) at a significantly higher incidence (55%) than did oocytes from small (11% to 20%) or medium (16%) follicles. Our findings are consistent with the hypotheses that a high proportion of oocytes from small antral follicles are atretic, and that a developmental program controls the molecular and cytogenetic changes occurring in porcine oocytes during follicular growth. These changes appear to be highly correlated with the acquisition of competency to complete maturation in vitro, and possibly also are required for normal fertilization and embryogenesis.

Calcium and meiotic maturation of the mammalian oocyte

“…Evidence suggests that the persistence of interphase characteristics in incompetent oocytes (Wickramasinghe et al, 1990) is due either to the lack of expression of certain cell cycle proteins required for meiotic competence, or the absence of posttranslational modifications that are required for their activity. In support of this hypothesis, incompetent oocytes show very different patterns of both polypeptide synthesis (McGaughey et al, 1979) and protein phosphorylation (Bornslaeger et al, 1988) compared with their competent counterparts. Moreover, although some MPF proteins are present in meiotically incompetent growing pig oocytes, they are incapable of being activated until the oocyte is fully grown (Christmann et al, 1993).…”

“…However, protein patterns clearly change with time during oocyte development well before the oocyte is fully grown and appear to be species-specific. Competency to undergo meiotic maturation, which is acquired during follicular development, is correlated with distinct changes in protein patterns in both mouse (Sorenson and Wassarman, 1976) and pig (McGaughey et al, 1979) oocytes. Since oocytes from small preantral follicles are not meiotically competent, it seems reasonable to assume that protein synthesis aRer this stage of development but before the oocytes are fully grown may be prerequisite for GVBD.…”

In vivo changes in oocyte germinal vesicle related to follicular quality and size at mid-follicular phase during stimulated cycles in the Cynomolgus monkey

“…Whatever the follicle quality, the zonae pellucidae of GV1 oocytes were never absent and showed normal morphology in more than 80% of cases studied. In healthy follicles, normal zonae pellucidae were more often observed around GV2 (Mandl, 1962), pig (McGaughey et al, 1979;Daguet, 1980), macaque (Thibault, 1974) and humans (Tesarik et al, 1983;Gougeon & Testart, 1986 (Hunter & Polge, 1966;Himelstein-Braw et al, 1976;Motlik & Fulka, 1976;Daguet, 1980;Gougeon, 1981;Thibault et al, 1987). Our results are in agreement with these observations, since we have observed a significant relationship between nuclear changes and germinal vesicle position in healthy follicles : the frequency of peripheral GV was higher in GV3 oocytes compared to GV1 (P < 0.001 ) and GV2 oocytes (P < 0.001 However, in a few cases GV migration occurred even in the GV1 oocyte.…”

Synchronization of In Vitro Maturation in Porcine Oocytes

“…A large variation in nuclear morphology of GV stage pig oocytes was found just after collection (Funahashi et al, 1997a;Nagai et al, 1997) and after a certain time of culture (Funahashi et al, 1997a). It has been shown that there are differences in GV configuration and polypeptide synthesis between oocytes obtained from different size antral follicles causing heterogeneity in overall developmental competence within oocytes, collected for IVM/IVF (Mcgaughey et al, 1979). Since the source of oocytes may differ (from different individuals and different size follicles), the developmental competence of GV stage pig oocytes used for IVM/IVF can also vary within the population used in one experiment.…”