Abstract
Chromosome structure is dramatically altered upon entering meiosis to establish chromosomal architectures necessary for the successful progression of meiosis-specific events. An early meiotic event involves the replacement of the non-SMC mitotic cohesins with their meiotic equivalents in most part of the chromosome, forming an axis on meiotic chromosomes. We previously demonstrated that the meiotic cohesin complex is required for chromosome compaction during meiotic prophase in the fission yeast Schizosaccharomyces pombe. These studies revealed that chromosomes are elongated in the absence of the meiotic cohesin subunit Rec8 and shortened in the absence of the cohesin-associated protein Pds5. In this study, using super-resolution structured illumination microscopy, we found that Rec8 forms a linear axis on chromosomes, which is required for the organized axial structure of chromatin during meiotic prophase. In the absence of Pds5, the Rec8 axis is shortened whereas chromosomes are widened. In rec8 or pds5 mutants, the frequency of homologous chromosome pairing is reduced. Thus, Rec8 and Pds5 play an essential role in building a platform to support the chromosome architecture necessary for the spatial alignment of homologous chromosomes.
Highlights
Meiosis is an important process for sexually reproducing eukaryotic organisms, generating inheritable haploid gametes from a parental diploid cell
In S. cerevisiae, Rec8 has been shown to be required for pairing in a cohesion-independent way (Brar et al 2009), and Pds5 is required for synapsis of homologous chromosomes in a Rec8dependent manner (Jin et al 2009)
Meiotic prophase-specific horsetail nuclear movements were observed in rec8- and pds5- mutant cells and microtubule dynamics were indistinguishable from those observed in wild-type cells, the shape of the horsetail nucleus appeared aberrant since chromatin structures were altered (Ding et al 2006)
Summary
Meiosis is an important process for sexually reproducing eukaryotic organisms, generating inheritable haploid gametes from a parental diploid cell. During this process, the pairing of homologous chromosomes results in recombinationmediated physical links between them that are essential for the correct segregation of meiotic chromosomes. The fission yeast Schizosaccharomyces pombe exhibits a striking example of the bouquet arrangement In this organism, the nucleus elongates and moves back and forth between the cell ends during meiotic prophase while telomeres remain clustered at the leading edge of the moving nucleus (Chikashige et al 1994; Ding et al 1998). Several mutants defective in telomere clustering and oscillatory chromosome movements exhibit a reduced frequency of homologous recombination, suggesting that these activities play a role in the pairing of homologous chromosomes
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