Fig. 9: Long-distance centromere-telomere communication in promoting meiotic entry.

Working model for telomere bouquet formation upon meiotic entry: i) During mitotic interphase, fission yeast cells display a conserved Rabl chromosome configuration. In this conformation, centromeres are positioned beneath the SPB thanks to the interaction between the LINC complex (Kms1/2-Sad1) and the kinetochore complex (inner and outer kinetochore), with the aid of Csi1 and Lem2 proteins. Also, telomeres are located in the NE, at the opposite site of the nucleus, based on the interaction between the Bqt3-Bqt4 complex and the Rap1-Taz1 complex. ii) At the onset of meiotic prophase, centromeres decluster from the SPB as the outer kinetochore disassembles, a process that may require a decrement of Cdk1 activity in the outer kinetochore region to facilitate centromere detachment. Following this, Cdc2/Cdk1 may be recycled and mobilized to the telomeres to promote their declustering. At this stage, telomere declustering facilitates their movement towards the SPB and the recruitment of bouquet proteins. iii) During prophase progression, centromere dissociation from the SPB is a prerequisite for telomere-SPB interaction, thanks to the recruitment of bouquet proteins (Bqt1 and Bqt2) to the LINC complex with the aid of the Bqt3-Bqt4 complex. iv) Bouquet formation occurs when centromeres are completely dissociated from the SPB. Then, telomeres are positioned beneath the SPB, based on the interaction between the LINC complex and the Rap1-Taz1 complex, which depends on the bouquet proteins (Bqt1 and Bqt2) and is aided by the Bqt3-Bqt4 complex.