Schematic model of nuclear organization in S. pombe meiosis. (A) The nuclear organization induced by the pat1 mutation. When meiosis is induced by Pat1 inactivation in the absence of the mating pheromone signaling, telomeres (green) cluster at the SPB (red); however, centromeres (blue) remain associated with the SPB, and the sister kinetochores are formed in a bipolar orientation. In these cells, the NMS complex (yellow) remains at the centromere attached to the SPB. (B) Nuclear organization induced by mating pheromone signal activation. Pat1 is inactivated downstream in the mating pheromone response, leading to telomere clustering. Centromere dissociation from the SPB and formation of the monopolar sister kinetochores are regulated, probably by independent pathways, downstream of mating pheromone signaling. It remains unknown whether centromere reconstruction and/or repositioning contributes to monopolar kinetochore formation (arrow with question mark).