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Abstract
Condensins are heteropentameric complexes that were first identified as structural components of mitotic chromosomes. They are composed of two SMC (structural maintenance of chromosomes) and three non-SMC subunits. Condensins play a role in the resolution and segregation of sister chromatids during mitosis, as well as in some aspects of mitotic chromosome assembly. Two distinct condensin complexes, condensin I and condensin II, which differ only in their non-SMC subunits, exist. Here, we used an RNA interference approach to deplete hCAP-D2, a non-SMC subunit of condensin I, in HeLa cells. We found that the association of hCAP-H, another non-SMC subunit of condensin I, with mitotic chromosomes depends on the presence of hCAP-D2. Moreover, chromatid axes, as defined by topoisomerase II and hCAP-E localization, are disorganized in the absence of hCAP-D2, and the resolution and segregation of sister chromatids are impaired. In addition, hCAP-D2 depletion affects chromosome alignment in metaphase and delays entry into anaphase. This suggests that condensin I is involved in the correct attachment between chromosome kinetochores and microtubules of the mitotic spindle. These results are discussed relative to the effects of depleting both condensin complexes.
ACKNOWLEDGMENTS
We thank U. K. Laemmli, T. Hirano, and J. M. Peters for providing some of the antibodies used in this study. We are also grateful to C. Kraft, S. Küng, and H. B. Osborne for critical reading of the manuscript. Microscopy analyses were performed thanks to the IFR97 microscopy service with the assistance of its manager, Stephanie Dutertre.
Our research is supported by grants from the Association pour la Recherche contre le Cancer, contract number 5711. CNRS UMR 6061 is a component of the Federative Research Institute IFR97, Functional Genomics and Health. E.W. was the recipient of a fellowship from the French Fondation pour la Recherche Médicale.