Abstract
The number of nuclear divisions in meiosis is strictly limited to two. Although the precise mechanism remains unknown, this seems to be achieved by adjusting the anaphase-promoting complex/cyclosome (APC/C) activity to degrade cyclin. Here, we describe a fission yeast cuf2 mutant that enters into a third nuclear division cycle, represented by ectopic spindle assembly and abnormal chromosome segregation. Cuf2 is a meiotic transcription factor, and its critical target is fzr1(+)/mfr1(+), which encodes a meiotic APC/C activator. fzr1Δ also enters a third nuclear division. Thus, Cuf2 ensures termination of the M-phase cycle by boosting Fzr1 expression to generate functional gametes.