Mechanism limiting centrosome duplication to once per cell cycle

The centrosome organizes the microtubule cytoskeleton and consists of a pair of centrioles surrounded by pericentriolar material. Cells begin the cell cycle with a single centrosome, which duplicates once before mitosis. During duplication, new centrioles grow orthogonally to existing ones and remain engaged (tightly opposed) with those centrioles until late mitosis or early G1 phase, when they become disengaged. The relationship between centriole engagement/disengagement and centriole duplication potential is not understood, and the mechanisms that control these processes are not known. Here we show that centriole disengagement requires the protease separase at anaphase, and that this disengagement licences centriole duplication in the next cell cycle. We describe an in vitro system using Xenopus egg extract and purified centrioles in which both centriole disengagement and centriole growth occur. Centriole disengagement at anaphase is independent of mitotic exit and Cdk2/cyclin E activity, but requires the anaphase-promoting complex and separase. In contrast to disengagement, new centriole growth occurs in interphase, is dependent on Cdk2/cyclin E, and requires previously disengaged centrioles. This suggests that re-duplication of centrioles within a cell cycle is prevented by centriole engagement itself. We propose that the 'once-only' control of centrosome duplication is achieved by temporally separating licensing in anaphase from growth of new centrioles during S phase. The involvement of separase in both centriole disengagement and sister chromatid separation would prevent premature centriole disengagement before anaphase onset, which can lead to multipolar spindles and genomic instability.     

全反式维甲酸对人真皮成纤维细胞RXR的表达影响

Ｎｏｒｔｈｅｒｎ杂交检测人真皮成纤维细胞维甲类Ｘ受体（ＲＸＲ）的表达。结果显示,细胞中只有ＲＸＲα和β的信息ＲＮＡ表达,无γ受体信息ＲＮＡ表达;用全反式维甲酸（ＡＴ－ＲＡ）刺激细胞于不同时段,对ＲＸＲ家族无诱导作用。表明人真皮成纤维细胞ＲＸＲ基因家族的表达调节完全不同于ＲＡＲ基因家族