Meiotic Chromosome Interactions: Nonhomologous Centromere (Un)Coupling and Homologous Synapsis

The fundamental function of meiosis, segregation of the maternal and paternal chromosomes, is facilitated by reciprocal recombination and intimate juxtaposition (synapsis) between the homologous chromosomes in meiotic prophase. Homolog synapsis, mediated by the synaptonemal complex (SC), is preceded by a stage of pairing between the centromeres of nonhomologous chromosomes. This pairing, named nonhomologous centromere coupling (NCC), depends upon the meiotic cohesin Rec8 and the SC protein Zip1. Nonhomologously coupled centromeres (NCCs), if remain tethered, must interfere with complete homolog synapsis (SC formation). Recent experiments demonstrate the existence of a mechanism that regulates NCC. Importantly, this is part of a regulatory network which couples dissolution of the NCCs with SC formation between the homologous chromosomes, thereby ensuring appropriate meiotic chromosome interactions. This paper reviews this network and presents speculations relating to the initiation of SC formation at centromere.