Nuclear ultrastructure in bovine oocytes after inhibition of meiosis by chemical and biological inhibitors

Abstract

Various components of the ovarian follicle as well as different chemicals can suppress the resumption of meiosis in cumulus-oocyte complexes (COCs). In this study the nuclear ultrastructure of bovine COCs was assessed after 8 h of meiotic inhibition with 50 microM roscovitine (ROSC), 50 microM butyrolactone (BL-I), 2 mM 6-DMAP, 2 microM cycloheximide (CX), or a theca cell monolayer (TC). COCs were recovered according to standard in vitro methods, cultured in a simple and defined medium, and processed for transmission electron microscopy. Control COCs were processed before onset of culture and multiple oocytes were evaluated for each treatment. In all groups, the oocyte nucleus presented a dense fibrillar nucleolus consisting of a fibrillar sphere with a fibrillar center. In TC and 6-DMAP inhibited COCs condensed chromatin adhered to the nucleolus while in all other groups the perinuclear chromatin was separated from the nucleolus. In ROSC inhibited COCs, the nuclear envelope presented only slight small amplitude undulation. The BL-I-inhibited COCs presented an intermediate level of low amplitude undulation of the NE. In CX, 6-DMAP, and TC inhibited COCs the nuclear envelope presented extensively low amplitude undulations. In ROSC inhibited COCs, electron-dense granules formed ring-shaped structures. In some of the BL-I inhibited COCs multiple stellate crystal-like structures were found, and in these COCs the nuclear envelope and the perinuclear cisternae appeared less distinct than in the other BL-I inhibited COCs. In 6-DMAP inhibited COCs interchromatin-like granule clusters were present. In conclusion, the oocyte nuclei in all COCs presented a dense fibrillar nucleolus resembling that in control COCs. However, variations were observed in 1) the nuclear envelope morphology; 2) the chromatin location in relation to the nucleolus; and 3) the presence of different populations of intranuclear granules. Although all treatments inhibited oocyte nucleus breakdown, the mechanisms underlying these effects are different and require further characterization. Mol. Reprod. Dev. 59: 459-467, 2001.

Bovine oocyte vitrification before or after meiotic arrest: effects on ultrastructure and developmental ability

“…Meiotic inhibition in vitro has been described to induce ultrastructural modifications in the bovine oocyte [11,17,18]. In the present work, meiotic arrest prior to IVM of fresh oocytes did not alter the structure of CC, which showed expansion and absence of morphological changes in organelles.…”

“…Although the cytoplasmic alterations observed in this work due to the meiotic arrest have been described elsewhere [17,18], the effects of cryopreservation in meiotically arrested oocytes are unknown. Our results show that combination of meiotic arrest and vitrification under our conditions is responsible for serious damages at the cellular level, making the oocytes unable to undergo IVF and subsequent embryonic development.…”

“…Thus, Faerge et al [17] described modifications in the nucleus of fresh bovine oocytes after meiotic inhibition with various chemical and biological inhibitors, and Lonergan et al [18] showed that inhibition of meiosis induced wide ultrastructural changes. Interestingly, these alterations coexist with embryonic development rates comparable to those of normal in vitro matured oocytes [19][20][21][22].…”

Birth of piglets after transferring of in vitro-produced embryos pre-matured with R-roscovitine

“…Specifically, the inhibitory effect of roscovitine on the cell cycle was discovered by Meijer (reviewed by Meijer & Raymond 2003). The results seem to demonstrate that it is more effective and produces less detrimental effects than other inhibitors such as cycloheximide (Faerge et al 2001), butyrolactone I (Kitagawa et al 1993, Meijer & Kim 1997, Fair et al 2002 or 6-DMAP (Lonergan et al 1997, Avery et al 1998, Liu et al 1998, Dode & Adona 2001.…”

Ultrastructure and Development of Vitrified/Warmed Bovine Oocytes Matured with 9-cis Retinoic Acid

“…The ultrastructure of the cumulus oocyte complexes (COC) is significantly affected by cryopreservation procedures. Several studies focused on cytoplasmic and nuclear alterations after cryopreservation within cumulus cells (CC) and the oocyte, [1][2][3][4][5][6][7] concluded that the reduced developmental competence of cryopreserved oocytes depends on cryodamage inflicted to the oocyte. 7,8 In the bovine oocyte, the maturation stage influences developmental competence after cryopreservation 1,[7][8][9][10][11] with the metaphase II (MII) oocyte being more resistant to cryopreservation than immature oocytes.…”