Depletion of topoisomerase IIalpha leads to shortening of the metaphase interkinetochore distance and abnormal persistence of PICH-coated anaphase threads.
Topoisomerase II (topo II) is a major component of mitotic chromosomes, and its unique decatenating activity has been implicated in many aspects of chromosome dynamics, of which chromosome segregation is the most seriously affected by loss of topo II activity in living cells. There is considerable evidence that topo II plays a role at the centromere including: the centromere-specific accumulation of topo II protein; cytogenetic/molecular mapping of the catalytic activity of topo II to active centromeres; the influence of sumoylated topo II on sister centromere cohesion; and its involvement in the activation of a Mad2-dependent spindle checkpoint. By using a human cell line with a conditional-lethal mutation in the gene encoding DNA topoisomerase IIalpha, we find that depletion of topo IIalpha, while leading to a disorganised metaphase plate, does not have any overt effect on general assembly of kinetochores. Fluorescence in situ hybridisation suggested that centromeres segregate normally, most segregation errors being chromatin bridges involving longer chromosome arms. Strikingly, a linear human X centromere-based minichromosome also displayed a significantly increased rate of missegregation. This sensitivity to depletion of topo IIalpha might be linked to structural alterations within the centromere domain, as indicated by a significant shortening of the distance across metaphase sister centromeres and the abnormal persistence of PICH-coated connections between segregating chromatids.
Spence
Jennifer M
JM
Department of Genetics, University of Cambridge, Downing Street, Cambridge CB2 3EH, UK.
Phua
Hui Hui
HH
Mills
Walter
W
Carpenter
Adam J
AJ
Porter
Andrew C G
AC
Farr
Christine J
CJ
D000705:Anaphase; D000951:Antigens, Neoplasm; D020090:Chromosome Segregation; D002877:Chromosomes, Human / Q000378:metabolism; D004265:DNA Helicases / Q000378:metabolism*; D004250:DNA Topoisomerases, Type II / Q000172:deficiency*; D004268:DNA-Binding Proteins / Q000172:deficiency*; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D018386:Kinetochores / Q000378:metabolism*; D008677:Metaphase
D000951:Antigens, Neoplasm; D004268:DNA-Binding Proteins; D007527:Isoenzymes; D004265:DNA Helicases; C516980:ERCC6L protein, human; D004250:DNA Topoisomerases, Type II