FEAR but not MEN genes are required for exit from meiosis I

Exit from mitosis is regulated by Cdc14, which plays an essential role in triggering cyclin-dependent kinase inactivation. Throughout most of the cell cycle, Cdc14 is sequestered in the nucleolus where it remains inactive. After the completion of anaphase, an essential signaling cascade, named the Mitotic Exit Network, or MEN, promotes Cdc14 release. Cdc14 is also released from the nucleolus in early anaphase by another, nonessential, pathway called FEAR (CdcFourteen Early Anaphase Release). Separase (Esp1), polo kinase (Cdc5), the kinetochore protein Slk19, and Spo12, whose molecular function remains unknown, have been identified as members of the FEAR pathway. In meiosis, mutations in CDC14 and its FEAR pathway regulators, CDC5, SLK19, and SPO12, all result it asci that contain only two diploid spores because of a defect in the ability to exit meiosis I. Thus although the FEAR pathway is dispensible for mitotic exit, it is essential for meiosis I exit. The way that the genes of the Mitotic Exit Network contribute to coordinating meiotic progression is less clear. Here, we explore this issue. Our results demonstrate that the orderly transition from meiosis I to meiosis II is accomplished by eliminating MEN function and using the FEAR pathway to modulate cyclin dependent kinase activity, in part through the actions of SIC1.