Condensins are Required for Maintenance of Nuclear Architecture

The 3-dimensional spatial organization of eukaryotic genomes is important for regulation of gene expression as well as DNA damage repair. It has been proposed that one basic biophysical property of all nuclei is that interphase chromatin must be kept in a condensed prestressed state in order to prevent entropic pressure of the DNA polymer from expanding and disrupting the nuclear envelope. Although many factors can contribute to specific organizational states to compact chromatin, the mechanisms through which such interphase chromatin compaction is maintained are not clearly understood. Condensin proteins are known to exert compaction forces on chromosomes in anticipation of mitosis, but it is not known whether condensins also function to maintain interphase prestressed chromatin states. Here we show that RNAi depletion of the N-CAP-H2, N-CAP-D3 and SMC2 subunits of human condensin II leads to dramatic disruption of nuclear architecture and nuclear size. This is consistent with the idea that condensin mediated chromatin compaction contributes significantly to the prestressed condensed state of the interphase nucleus, and when such compaction forces are disrupted nuclear size and shape change due to chromatin expansion.