CDC6 regulates both G2/M transition and metaphase‐to‐anaphase transition during the first meiosis of mouse oocytes

• Published in: Journal of cellular physiology Vol. 235; no. 7-8; pp. 5541 - 5554
• Main Authors: Yi, Zi‐Yun, Meng, Tie‐Gang, Ma, Xue‐Shan, Li, Jian, Zhang, Chun‐Hui, Ouyang, Ying‐Chun, Schatten, Heide, Qiao, Jie, Sun, Qing‐Yuan, Qian, Wei‐Ping
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01.07.2020
• Subjects: Anaphase; Anaphase - genetics; Animals; Assembly; Cdc2 protein; CDC6; Cell culture; Cell Cycle Proteins - genetics; Cell division; Centrosome; Chromosomes; Cycle protein; Cyclin B1; Deoxyribonucleic acid; Depletion; DNA; DNA biosynthesis; E-cadherin; Extrusion; Female; G2 Phase Cell Cycle Checkpoints - genetics; Gametocytes; germinal vesicle breakdown; Localization; M Phase Cell Cycle Checkpoints - genetics; Meiosis; Meiosis - genetics; Metaphase; Metaphase - genetics; Mice; Nuclear Proteins - genetics; oocyte; Oocytes; Oocytes - growth & development; Oocytes - metabolism; Phenotypes; Phosphorylation; Replication initiation; spindle; Spindle Apparatus - genetics; Spindles; Tubulin; meiosis; oocyte; CDC6; spindle; germinal vesicle breakdown
• ISSN: 0021-9541; 1097-4652; 1097-4652
• DOI: 10.1002/jcp.29469

Cell division cycle protein, CDC6, is essential for the initiation of DNA replication. CDC6 was recently shown to inhibit the microtubule‐organizing activity of the centrosome. Here, we show that CDC6 is localized to the spindle from pro‐metaphase I (MI) to MII stages of oocytes, and it plays important roles at two critical steps of oocyte meiotic maturation. CDC6 depletion facilitated the G2/M transition (germinal vesicle breakdown [GVBD]) through regulation of Cdh1 and cyclin B1 expression and CDK1 (CDC2) phosphorylation in a GVBD‐inhibiting culture system containing milrinone. Furthermore, GVBD was significantly decreased after knockdown of cyclin B1 in CDC6‐depleted oocytes, indicating that the effect of CDC6 loss on GVBD stimulation was mediated, at least in part, by raising cyclin B1. Knockdown of CDC6 also caused abnormal localization of γ‐tubulin, resulting in defective spindles, misaligned chromosomes, cyclin B1 accumulation, and spindle assembly checkpoint (SAC) activation, leading to significant pro‐MI/MI arrest and PB1 extrusion failure. These phenotypes were also confirmed by time‐lapse live cell imaging analysis. The results indicate that CDC6 is indispensable for maintaining G2 arrest of meiosis and functions in G2/M checkpoint regulation in mouse oocytes. Moreover, CDC6 is also a key player regulating meiotic spindle assembly and metaphase‐to‐anaphase transition in meiotic oocytes. Our paper showed that the depletion of cell division cycle‐6 (CDC6) facilitated G2/M transition by elevating cyclin B1 levels and decreasing Cdh1 levels. While the accelerated G2/M transition induced by CDC6 knockdown could be rescued by injecting cyclin B1 small interfering RNA. Furthermore, our results showed that CDC6 localized along the meiotic spindle and plays a crucial role in spindle assembly, metaphase‐to‐anaphase transition, and subsequent first polar body extrusion in meiotic oocytes.