Fair T, Hulshof S C, Hyttel P, Greve T, Boland M
Department of Anatomy and Physiology, Royal Veterinary and Agricultural University, Frederiksberg C, Denmark.
Mol Reprod Dev. 1997 Feb;46(2):208-15. doi: 10.1002/(SICI)1098-2795(199702)46:2<208::AID-MRD11>3.0.CO;2-X.
An understanding of the recruitment and growth of follicles within the bovine ovary is crucial to their successful exploitation in vitro. The aim of the present study was to describe the nuclear ultrastructure and transcriptional activity of primordial to early tertiary follicular oocytes from bovine adult ovaries. Small blocks of ovarian cortex were incubated in medium enriched with 3H-uridine for 30 min. Subsequently, the tissue blocks were fixed in Karnowsky's fixative, dehydrated, epon embedded, sectioned (2 microns), processed for autoradiography, and examined under light microscopy. Sections showing preantral follicles with presumptive oocyte nucleoli were reembedded for transmission electron microscopy. The follicles were divided into five categories: 1) resting primordial, with a single layer of flattened granulosa cells, 2) activated primordial, with a single layer of flattened and some cuboidal granulosa cells, 3) primary, with a single layer of cuboidal granulosa cells, 4) secondary, with a complete or incomplete bilayer of cuboidal cells, and 5) tertiary, with more than two layers of granulosa cells delineating one or more intercellular cavities. The granulosa cells of all follicle classes were transcriptionally active. However, the oocytes did not display transcriptional activity, as measured by the present means, until the secondary and tertiary follicular stages. The oocyte nucleolus was granular in the primordial follicles. Following follicular activation, fibrillar centres invaded the nucleolus and, in the early tertiary follicle, numerous fibrillar centres were distributed throughout the nucleolus. In conclusion, the oocyte nucleolar function is gradually activated at follicle activation, and oocyte transcription is initiated at approximately the time of the secondary follicle stage.
了解牛卵巢内卵泡的募集和生长对于在体外成功利用它们至关重要。本研究的目的是描述来自成年牛卵巢的原始卵泡至早期三级卵泡卵母细胞的核超微结构和转录活性。将小块卵巢皮质在富含3H-尿苷的培养基中孵育30分钟。随后，将组织块用卡诺氏固定液固定，脱水，环氧树脂包埋，切片（2微米），进行放射自显影处理，并在光学显微镜下检查。显示有假定卵母细胞核仁的窦前卵泡的切片重新包埋用于透射电子显微镜检查。卵泡分为五类：1）静止原始卵泡，有单层扁平颗粒细胞；2）激活原始卵泡，有单层扁平颗粒细胞和一些立方形颗粒细胞；3）初级卵泡，有单层立方形颗粒细胞；4）次级卵泡，有完整或不完整的立方形细胞双层；5）三级卵泡，有两层以上颗粒细胞界定一个或多个细胞间腔。所有卵泡类别的颗粒细胞都具有转录活性。然而，用目前的方法测量，卵母细胞直到次级和三级卵泡阶段才显示转录活性。原始卵泡中的卵母细胞核仁呈颗粒状。卵泡激活后，纤维中心侵入核仁，在早期三级卵泡中，大量纤维中心分布在整个核仁中。总之，卵母细胞核仁功能在卵泡激活时逐渐被激活，卵母细胞转录大约在次级卵泡阶段开始。
