Nucleolar transformations in the human oocyte after completion of growth

Abstract

Nucleolar ultrastrure was studied in fully grown human oocytes obtained from multilaminar preantral follicles and from follicles at different stages of antrum formation. Selective staining for ribonucleoproteins and 3H‐uridine labeling were used in attempt to better understand the nature and functional significance of homogeneous dense nucleoli found in oocytes from large antral follicles. There was an apparent increase in the radio of nucleonema to nucleolar interstices, accompanied by a gradual degranulation of the nucleolonema during early stages of antrum fromation. The process of nucleolar homogenization continued in oocytes from medium‐size antralfollicles, island of more tightly packed fibrils being hybothesized to represent persisting active transcription units. Entirely filamentous and homogeneous nucleoli were typical for oocytes from large antral follicles. They were demonstrated to ribonucleoprotein filaments embedded in pale‐ staining matrix. They were demonstrated to contain newly synthesized RNA after a 30‐min pulse with 3H‐uridine. The described nucleolar transformations are interpreted as acorrelate of nucleolar transition from a site of RNA synthesis into a site of RNA Storage during in human oocyte preovulatory development.

Germinal vesicle chromatin configurations of bovine oocytes

“…Goat oocytes became MII-competent in 2-5 mm follicles (Crozet et al, 1995;De Smedt et al, 1994;Ma et al, 2003) and the percentage of NSN (GV1) oocytes decreased to 16% in 1-1.8 mm follicles (Sui et al, 2005). A dramatic decrease in RNA synthesis has been observed in oocytes of pigs (Crozet et al, 1981) and human beings (Tesarik et al, 1983) with follicular growth, and a direct link between the presence of the perinucleolar ring chromatin and transcriptional inactivity has been reported in growing oocytes of mice (Bouniol-Baly et al, 1999;Debey et al, 1993;Vautier et al, 1994) and human beings (Miyara et al, 2003;Parfenov et al, 1989). Therefore, our results suggest that (i) the NSN is a juvenile chromatin pattern, and oocytes must end this configuration before they gain the full meiotic competence; (ii) the presence of the perinucleolar ring chromatin was also linked with the transcriptional inactivity and meiotic competence in bovine oocytes.…”

“…In pigs (Sun et al, 2004) and goats (Sui et al, 2005), oocyte GV chromatin was also synchronized in a less condensed state before GVBD. The Incorporation of [ 3 H] uridine by the preovulatory GV oocytes has also been reported in mice (Bloom et al, 1972;Kopecny et al, 1995;Rodman and Bachvarova., 1976;Wassarman et al, 1976) and in human beings (Tesarik et al, 1983(Tesarik et al, , 1984.…”

“…A common feature in the configuration of GV chromatin in most species is that the diffuse chromatin (the socalled nonsurrounded nucleolar [NSN] pattern) condenses into a perinucleolar ring (the so-called sur-rounded nucleolar [SN] configuration) during follicular growth (mice: Debey et al, 1993;Mattson and Albertini, 1990;Wickramasinghe et al, 1991;Zuccotti et al, 1995;pig: Guthrie and Garrett, 2000;Motlik and Fulka, 1976;Sun et al, 2004;horse: Hinrichs, 1997;Hinrichs et al, 1993;monkey: Lefevre et al, 1989;Schramm et al, 1993;human being: Miyara et al, 2003;Parfenov et al, 1989;Tesarik et al, 1983). However, studies are few and the results are conflicting on the configuration of GV chromatin in bovine oocytes.…”

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.…”

“…Oocyte nuclear modifications therefore appear to be a prerequisite to resumption of meiosis. GVBD has also been noted in atretic ovarian follicles (Thibault, 1974;Gougeon & Testart, 1986 (Thibault & G6rard, 1971;Sanyal ef al., 1976;Daguet, 1980;Tesarik et al, 1983;Gougeon & Testart, 1986). …”