Set1- and Clb5-deficiencies disclose the differential regulation of centromere and telomere dynamics in Saccharomyces cerevisiae meiosis.

Résumé

The entry into meiosis is characterized by a lengthy premeiotic S phase and a reorganization of the nuclear architecture. Analysis of centromere and telomere dynamics in wild-type Saccharomyces cerevisiae meiosis suggests that resolution of vegetative centromere and telomere clusters are independent events differently connected to premeiotic S phase. Absence of the B-type cyclin Clb5 or the Set1 histone methyltransferase leads to a delay of premeiotic S phase by separate mechanisms. In clb5Delta cells, centromere cluster resolution appears normal, whereas dissolution of the vegetative telomere clusters is impaired and meiosis-specific clustering of telomeres, i.e. bouquet formation, is grossly delayed. In set1Delta cells, centromere and telomere redistribution are both impaired and bouquet nuclei are absent, despite proper location of the meiosis-specific telomere protein Ndj1. Thus, centromere and telomere redistribution at the onset of prophase I is differentially regulated, with centromere dispersion occurring independently of premeiotic S phase. The normal kinetics of dissolution of the vegetative telomere clusters in a set1Delta mec1-1 mutant suggests the presence of a checkpoint that limits the dispersion of telomeres in absence of Set1.