Distinct functions of condensin I and II in mitotic chromosome assembly

Abstract

Condensin is a protein complex associated with mitotic chromosomes that has been implicated in chromosome condensation. In vertebrates, two types of condensin complexes have recently been identified, called condensin I and II. Here, we show that in mammalian cells condensin II associates with chromatin in prophase, in contrast to condensin I which is cytoplasmic and can thus interact with chromosomes only after nuclear envelope breakdown. RNA interference experiments in conjunction with imaging of live and fixed cells revealed that condensin II is required for chromosome condensation in early prophase, whereas condensin I appears to be dispensable at this stage. By contrast, condensin I is required for the complete dissociation of cohesin from chromosome arms, for chromosome shortening and for normal timing of progression through prometaphase and metaphase, whereas normal condensin II levels are dispensable for these processes. After depletion of both condensin complexes, the onset of chromosome condensation is delayed until the end of prophase, but is then initiated rapidly before nuclear envelope breakdown. These results reveal that condensin II and I associate with chromosomes sequentially and have distinct functions in mitotic chromosome assembly.

MTB, the murine homolog of condensin II subunit CAP-G2, represses transcription and promotes erythroid cell differentiation

“…We found that Stem cell leukemia can promote the nuclear localization of MTB We next investigated whether MTB localizes to the nucleus, similar to hCAP-G2. 1,23,24 We generated two different MTB-EGFP fusion constructs, linking the EGFP cassette to either the 5 0 or the 3 0 end of full-length MTB protein, and transfected both constructs into COS cells to visualize the cellular localization of MTB protein. Surprisingly, we observed that both EGFP-MTB and MTB-EGFP were largely restricted to the cytoplasm (Figure 2d, i-ii, and data not shown).…”

Condensin Regulates the Stiffness of Vertebrate Centromeres

“…Condensin is important for the architecture of mitotic chromosome arms (Coelho et al, 2003;Hudson et al, 2003;Hirota et al, 2004;Hirano, 2006), but it also localizes to centromeres (Saitoh et al, 1994;Gerlich et al, 2006), where condensin I, but not condensin II was reported to have a role in stabilizing the structure (Gerlich et al, 2006). It has recently been suggested that condensin could have a role in regulating the elastic behavior of centromeric chromatin.…”

“…Centromere and kinetochore tension and stretch are important for maintaining chromosome alignment (McIntosh et al, 2002), stabilizing kinetochore microtubule (kMT) attachments (Nicklas and Koch, 1969), spindle checkpoint signaling (Musacchio and Salmon, 2007;McEwen and Dong, 2009), and also for the back-to-back orientation of sister kinetochores (Loncarek et al, 2007). At least three independent factors have roles in the establishment of centromeric tension in metaphase: sister chromatid cohesion (Yeh et al, 2008), the elastic properties of chromatin (Houchmandzadeh et al, 1997;Almagro et al, 2004;Marko, 2008), and the higher order structure of the centromeric chromatin.Condensin is important for the architecture of mitotic chromosome arms (Coelho et al, 2003;Hudson et al, 2003;Hirota et al, 2004;Hirano, 2006), but it also localizes to centromeres (Saitoh et al, 1994;Gerlich et al, 2006), where condensin I, but not condensin II was reported to have a role in stabilizing the structure (Gerlich et al, 2006). It has recently been suggested that condensin could have a role in regulating the elastic behavior of centromeric chromatin.…”

Molecular and Genetic Analysis of Condensin Function in Vertebrate Cells

“…The two forms of condensin, condensin I and II, are pentameric complexes composed of the SMC2 and SMC4 ATPases plus three auxiliary subunits (CapG/G2, CapD2/D3, and CapH/H2) (Ono et al, 2003;Hirota et al, 2004). The two SMC subunits are known to be responsible for ATPase activity, which is essential for condensin function (Stray and Lindsley, 2003).…”