Homologous chromosome pairing in Schizosaccharomyces pombe

Abstract

Homologous chromosome pairing is a central feature of meiosis I, contributing to the correct segregation of chromosomes during meiosis. The fission yeast, Schizosaccharomyces pombe, has been widely used to study meiotic chromosome dynamics, partly because studies in this yeast are simplified due to the lack of postpairing synaptic structures. Chromosome pairing in Sz. pombe occurs differentially throughout the genome. Telomeres cluster at the spindle pole body (SPB) at the onset of meiosis, imposing a spatial restriction on pairing events. Subsequently, centromeres dissociate from the SPB and pair in a recombination-and heterochromatin (Swi6)-independent fashion. Pairing of telomere distal regions occurs during meiotic prophase, concomitant with a dynamic association/dissociation of homologous regions, with interhomologue associations becoming increasingly stable. The stabilization of paired regions is enhanced by factors required for the initiation of meiotic recombination, suggesting that recombination stabilizes paired regions. However, substantial pairing is initiated in the absence of recombination; this is dependent upon another factor, the conserved Meu13 protein, demonstrating that recombination is not required for initial pairing interactions. During meiotic prophase Sz. pombe exhibits a pronounced dynein-dependent nuclear oscillation, which drives the pairing of centromeric and interstitial regions. Dynein is also required for the significant levels of achiasmate reductional segregation observed in Sz. pombe, possibly implicating the centromere-associated pairing with achiasmate homologue segregation. Whilst Sz. pombe does not form discernable synaptic structures continuously along the meiotic chromosomes, it does form proteinacious, meiosis-specific, linear structures (linear elements). However, the role, if any, of these structures in mediating homologue pairing is unknown.

A Role for Dynein in the Inhibition of Germ Cell Proliferative Fate

“…2B and C). Our observation of polyploidy is consistent with previously described roles for dynein in mitotic cell division across taxa (16,25,37,42,58), while the observation of unpaired diakinetic chromosomes extends those of previous studies that have demonstrated a role for dynein in mediating homologous chromosome pairing in fission yeast (12,60,61). At first glance, these findings appear paradoxical because the germ line tumors in the glp-1 gain-offunction background require additional mitotic divisions.…”

Linear Element-Independent Meiotic Recombination in Schizosaccharomyces pombe

“…However, the exact role of these structures remains unclear (Loidl 2006;Wells et al 2006). Whether or not recombination can occur outside the context of LinEs has developed into a central question.…”

Dynamic chromosome movements during meiosis: a way to eliminate unwanted connections?

“…concomitant with SC formation and thus well into the recombination process, when stable strand exchange intermediates are already formed between homologous interacting DNAs [7, 21-23]. Additionally, in both fission yeast and budding yeast, mutations conferring disruption of telomere motion have only relatively modest effects on either recombination or pairing [24, 25, 46, 54]. Finally, in the three organisms studied, the movements of mid-prophase chromosomes have a back-and-forth character (rotationally within rat spermatocytes nuclei, longitudinally in S. pombe , and circum-nuclear in S. cerevisiae ), which does not have the effect of ‘stirring’ chromosomes (Figure 1).…”