De La Fuente R, Eppig J J
The Jackson Laboratory, Bar Harbor, Maine 04609, USA.
Dev Biol. 2001 Jan 1;229(1):224-36. doi: 10.1006/dbio.2000.9947.
Chromatin configuration in the germinal vesicle (GV) undergoes dynamic changes during oocyte growth, yet little is known about the mechanisms regulating chromatin remodeling in mouse oocytes. The hypothesis that companion granulosa cells play a role in modulating chromatin configuration and subsequent transcriptional activity in the oocyte genome was tested. Analysis of transcriptional activity, as determined by Br-UTP incorporation, revealed a similar percentage of transcriptionally active and inactive oocytes present in the large antral follicles of mature females. However, gonadotropin stimulation of follicular development induced an increase in the proportion of transcriptionally inactive oocytes. Interestingly, a similar proportion of stage-matched, oocyte-granulosa cell complexes grown in vitro without gonadotropin stimulation displayed chromatin redistribution around the nucleolus and no transcriptional activity. In contrast, when cultured in the absence of companion granulosa cells, transcriptional activity remained unabated in the majority of denuded GV stage oocytes. Extended prophase arrest in fully grown transcriptionally inactive oocyte-granulosa cell complexes had no effect on the progression of meiosis after in vitro maturation. However, it reduced the competence to complete preimplantation embryo development. These results indicate that chromatin redistribution around the nucleolus is associated with transcriptional repression in the GV of both fully grown in vivo-derived oocytes and cultured oocyte-granulosa cell complexes. Moreover, the results presented here suggest that some aspects of intraovarian control mechanisms were abrogated during culture of oocyte-granulosa cell complexes, resulting in a higher proportion of oocytes with "mature" chromatin. Most importantly, companion granulosa cells played an active role in modulating the transcriptional activity of the oocyte genome.
在卵母细胞生长过程中，生发泡（GV）中的染色质构型会发生动态变化，但对于调节小鼠卵母细胞染色质重塑的机制却知之甚少。我们对伴行颗粒细胞在调节卵母细胞基因组染色质构型及后续转录活性中发挥作用这一假说进行了验证。通过溴尿嘧啶三磷酸（Br-UTP）掺入法测定转录活性，分析结果显示，成熟雌性大鼠大卵泡中存在的转录活性和非活性卵母细胞比例相似。然而，促性腺激素刺激卵泡发育会导致转录非活性卵母细胞比例增加。有趣的是，在无促性腺激素刺激条件下体外培养的阶段匹配的卵母细胞-颗粒细胞复合体中，有相似比例的细胞显示染色质在核仁周围重新分布且无转录活性。相反，在没有伴行颗粒细胞的情况下培养时，大多数裸卵GV期卵母细胞的转录活性仍未减弱。在完全生长的转录非活性卵母细胞-颗粒细胞复合体中延长前期阻滞对体外成熟后的减数分裂进程没有影响。然而，它降低了完成植入前胚胎发育的能力。这些结果表明，在体内来源的完全生长的卵母细胞和培养的卵母细胞-颗粒细胞复合体的GV中，核仁周围的染色质重新分布与转录抑制相关。此外，本文给出的结果表明，在卵母细胞-颗粒细胞复合体培养过程中，卵巢内控制机制的某些方面被废除，导致具有“成熟”染色质的卵母细胞比例更高。最重要的是，伴行颗粒细胞在调节卵母细胞基因组的转录活性中发挥了积极作用。
