核黃素激酶調節有絲分裂的意外作用

Abstract

為了確保細胞內基因的穩定性，在有絲分裂期間調節染色體分離是非常重要的一個過程。有絲分裂主要是由細胞週期蛋白所調控，但合適的營養條件對於細胞週期的影響也是非常重要。有趣的是，我們發現產生能量的輔因子:黃素單核苷酸（FMN）在調節有絲分裂中具有重要的角色，黃素單核苷酸 是由核黄素激酶 （Fmn1）催化核黄素 (維生素B2) 所形成。在酵母菌中，細胞週期結束時必須要透過mitotic exit network（MEN） 的訊息調節，而Lte1 是MEN的正調控因子。和組蛋白修飾有關的基因，SET1，也被報導和mitotic exit有關。有趣的是，我們發現FMN1 和SET1 還有LTE1皆有基因相互作用。我證實了有絲分裂的延遲造成此基因相互作用，而且，FMN1的功能與MEN是平行的，因為FMN1會表現出與CLA4和CDC15有基因的相互作用，而此兩者都是參與MEN的調控。另外，lte1Δ fmn1Δ 的生長缺陷可以通過缺失BUB2來解救。而BUB2是MEN的負調控因子，也就是說，我發現，很重要地，FMN1會與細胞週期的調控有關，而且是跟mitotic exit network有平行關係。更進一步地，我們發現FMN1參與在anaphase promoting complex (APC）中，而且會有metaphase-anaphase時期轉換的缺陷。Ras2 會抑制APC的功能，而我們發現 fmn1突變體的生長缺陷可通過缺失RAS2 而得以挽救。我們也發現了fmn1突變體中表現APC缺陷的症狀: fmn1突變體導致染色體分離錯誤和有絲分裂週期蛋白Clb2的異常積累。綜上所述，FMN1缺陷會導致metaphase和anaphase轉換上出現錯誤。因此，FMN1可能在調節有絲分裂中扮演重要的角色。

The regulation of chromosome separation during the mitotic phase is essential to ensure genome stability. Mitosis is controlled by complex regulation network, including proper nutritional and metabolic status to ensure smooth cell cycle transition. Interestingly, our genetic screening identified that an energy producing cofactor, flavin mononucleotide (FMN) has an important function in regulating mitosis in budding yeast. The Mitotic Exit Network (MEN) is a signaling pathway known to drive cells out of mitosis and to promote the faithful division of cells. We found that FMN1, encoding a Riboflavin kinase, confers a genetic interaction with LTE1, coding for a positive regulator of MEN. In addition, FMN1 displayed negative interactions with CLA4 and CDC15, both of which are involved in the regulation of MEN. Furthermore, the growth defect of lte1Δ fmn1Δ could be rescued by the deletion of BUB2, which is a negative regulator to the MEN activity. The growth defect of fmn1Δ could be rescued by the deletion of RAS2, which inhibits the function of anaphase promoting complex (APC), indicating that the Fmn1 may play a role in regulating APC. Furthermore, the fmn1Δ mutants exhibited anaphase entry delay, chromosome segregation error and abnormally accumulation of mitotic cyclin, Clb2. Taken together, ablation of FMN1 leads to defects in metaphase-anaphase transition. Thus, FMN1 may play a role in regulating mitosis.