Aktas Huseyin, Leibfried-Rutledge M Lorainne, First Neal L
Department of Meat and Animal Studies, University of Wisconsin Madison, Madison, Wisconsin, USA.
Mol Reprod Dev. 2003 Jul;65(3):336-43. doi: 10.1002/mrd.10287.
Bovine oocytes are arrested at the prophase of first meiotic cell cycle. Meiosis resumes in oocytes of pre-ovulatory follicles upon LH surge. However, oocytes from secondary follicles spontaneously resume meiosis in the absence of hormones if removed from the follicle and cultured in vitro. The nature of meiotic arrestor in bovine follicles is poorly understood. In this study we investigated the role of cell-cell interactions between granulosa and cumulus cells and the oocyte in mediating maintenance of meiotic arrest by cAMP. We sorted oocytes as granulosa-cumulus oocyte complexes (GCOC) if surrounded with cumulus cells attached to a large granulosa investment or cumulus oocytes complexes (COC) if surrounded with cumulus cells only and investigated the role cAMP in maintenance of meiotic arrest in these oocytes under various conditions. In hormone- and serum-free medium both GCOC and COC enclosed oocytes resumed meiosis. When cAMP was elevated with addition of invasive adenylate cyclase (iAC) GCOC enclosed oocytes were maintained in the prophase with intact germinal vesicle (GV) while COC enclosed oocytes underwent GV breakdown (GVBD). iAC elevated cAMP in both types of oocytes to the same level. If oocytes were liberated from the cumulus and granulosa cells, they re-initiated meiosis in serum and hormone free medium, but remained in the GV stage if iAC was added to the medium. Untreated GCOC and COC enclosed oocytes extruded first polar body at the same frequency in hormone-supplemented media. GCOC and COC enclosed oocytes but not denuded oocytes (DO) cultured without somatic cells acquired developmental competence if cultured in hormone-containing medium. It is concluded that maintenance of meiotic arrest is regulated by the interplay of cAMP, and cumulus and granulosa cells.
牛卵母细胞停滞于第一次减数分裂细胞周期的前期。促黄体生成素（LH）峰出现时，排卵前卵泡中的卵母细胞减数分裂恢复。然而，如果从卵泡中取出并在体外培养，次级卵泡中的卵母细胞在没有激素的情况下会自发恢复减数分裂。牛卵泡中减数分裂阻滞因子的性质尚不清楚。在本研究中，我们研究了颗粒细胞、卵丘细胞与卵母细胞之间的细胞间相互作用在通过环磷酸腺苷（cAMP）介导减数分裂阻滞维持中的作用。如果卵母细胞被附着有大量颗粒细胞的卵丘细胞包围，我们将其分类为颗粒-卵丘卵母细胞复合体（GCOC）；如果仅被卵丘细胞包围，则分类为卵丘卵母细胞复合体（COC），并研究了在各种条件下cAMP在维持这些卵母细胞减数分裂阻滞中的作用。在无激素和无血清培养基中，GCOC和COC包裹的卵母细胞均恢复减数分裂。当通过添加侵入性腺苷酸环化酶（iAC）提高细胞内cAMP（cAMP）水平时，GCOC包裹的卵母细胞保持在前期，生发泡（GV）完整，而COC包裹的卵母细胞则发生生发泡破裂（GVBD）。iAC使两种类型的卵母细胞中的cAMP升高到相同水平。如果将卵母细胞从卵丘细胞和颗粒细胞中分离出来，它们在无血清和无激素培养基中会重新启动减数分裂，但如果向培养基中添加iAC，则会停留在GV期。在添加激素的培养基中，未经处理的GCOC和COC包裹的卵母细胞以相同频率排出第一极体。如果在含激素的培养基中培养，GCOC和COC包裹的卵母细胞（而非没有体细胞的裸卵（DO））在无体细胞培养时获得发育能力。结论是，减数分裂阻滞的维持受cAMP以及卵丘细胞和颗粒细胞相互作用的调节。
