![]() cerevisiae and Schizosaccharomyces pombe), and DNA damage response and repair ( Heale et al., 2006 Johzuka et al., 2006 Haeusler et al., 2008 Csankovszki et al., 2009 Iwasaki et al., 2010 Sakamoto et al., 2011). In addition, condensin has been shown to function in dosage compensation ( Caenorhabditis elegans), maintenance of rDNA repeats ( Saccharomyces cerevisiae), tRNA gene clustering ( S. Condensin is proposed to act by encircling or extruding multiple DNA loops within the same chromatid, thus promoting or ensuring chromosome compaction ( Nasmyth, 2001 Cuylen et al., 2011). Subsequent studies in diverse organisms have shown it to be a highly conserved structural component of chromosomes that is important for proper chromosome segregation during both mitosis and meiosis (reviewed in Hirano, 2012, 2016). We propose that failure to form discrete chromosome territories is the common cause of the defects observed in the absence of condensins.Ĭondensin is a multi-subunit protein complex that was originally identified as a primary requirement for chromosome condensation in cell-free Xenopus oocyte extracts ( Hirano and Mitchison, 1994). Condensin depletion also fundamentally altered chromosome arrangement in the polyploid somatic nucleus: multiple copies of homologous chromosomes tended to cluster, consistent with a previous model of condensin suppressing default somatic pairing. Live imaging of meiotic divisions in condensin-depleted cells showed repeated nuclear stretching and contraction as the chromosomes failed to separate. In condensin-depleted cells, a chromosome condensation defect was most striking at meiotic metaphase, when Tetrahymena chromosomes are normally most densely packaged. ![]() Mitosis and meiosis of the germline nucleus and amitotic division of the somatic nucleus are all dependent on condensins. Consistent with their functional specializations in sexual reproduction and gene expression, condensins of the germline nucleus and the polyploid somatic nucleus are composed of different subunits. In Tetrahymena, the germline and soma are partitioned into two different nuclei within a single cell. We studied condensin in the evolutionarily distant protist model Tetrahymena, which features noncanonical nuclear organization and divisions. Condensin is a protein complex with diverse functions in chromatin packaging and chromosome condensation and segregation.
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