RNAi analysis reveals an unexpected role for topoisomerase II in chromosome arm congression to a metaphase plate.
DNA topoisomerase II (Topo II) is a major component of mitotic chromosomes and an important drug target in cancer chemotherapy, however, its role in chromosome structure and dynamics remains controversial. We have used RNAi to deplete Topo II in Drosophila S2 cells in order to carry out a detailed functional analysis of the role of the protein during mitosis. We find that Topo II is not required for the assembly of a functional kinetochore or the targeting of chromosomal passenger proteins, nonetheless, it is essential for anaphase sister chromatid separation. In response to a long-running controversy, we show that Topo II does have some role in mitotic chromatin condensation. Chromosomes formed in its absence have a 2.5-fold decrease in the level of chromatin compaction, and are morphologically abnormal. However, it is clear that the overall programme of mitotic chromosome condensation can proceed without Topo II. Surprisingly, in metaphase cells depleted of Topo II, one or more chromosome arms frequently stretch out from the metaphase plate to the vicinity of the spindle pole. This is not kinetochore-based movement, as the centromere of the affected chromosome is located on the plate. This observation raises the possibility that further unexpected functions for Topo II may remain to be discovered.
Chang
Chih-Jui
CJ
Wellcome Trust Centre for Cell Biology, Institute for Cell and Molecular Biology, Kings Buildings, University of Edinburgh, Mayfield Road, Edinburgh EH9 3JR, Scotland, UK.
Goulding
Sarah
S
Earnshaw
William C
WC
Carmena
Mar
M
D000705:Anaphase / Q000502:physiology*; D000818:Animals; D002455:Cell Division; D002843:Chromatin / Q000378:metabolism; D004250:DNA Topoisomerases, Type II / Q000378:metabolism*; D004330:Drosophila / Q000378:metabolism; D006657:Histones / Q000378:metabolism; D018386:Kinetochores / Q000378:metabolism*; D008677:Metaphase / Q000502:physiology*; D008856:Microscopy, Fluorescence; D010766:Phosphorylation; D034741:RNA, Small Interfering / Q000378:metabolism*; D008941:Spindle Apparatus / Q000378:metabolism; D059005:Topoisomerase II Inhibitors
D002843:Chromatin; D006657:Histones; D034741:RNA, Small Interfering; D059005:Topoisomerase II Inhibitors; D004250:DNA Topoisomerases, Type II