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Abstract:
The assembly of mitotic chromosomes is controlled by
condensin complexes. In vertebrates, condensin I binds to
chromatin in prometaphase, confers rigidity to
chromosomes and enables the release of cohesin complexes
from chromosome arms, whereas condensin II associates
with chromosomes in prophase and promotes their
condensation. Both complexes are essential for
chromosome segregation in anaphase. Although the
association of condensins with chromatin is important for
the assembly and segregation of mitotic chromosomes, it is
poorly understood how this process is controlled. Here we
show that the mitotic kinase Aurora B regulates the
association of condensin I, but not the interaction of
condensin II with chromatin. Quantitative time-lapse
imaging of cells expressing GFP-tagged condensin subunits
revealed that Aurora B is required for efficient loading of
condensin I onto chromosomes in prometaphase and for
maintenance of the complex on chromosomes in later stages
of mitosis. The three non-SMC subunits of condensin I are
Aurora B substrates in vitro and their mitosis-specific
phosphorylation depends on Aurora B in vivo. Our data
indicate that Aurora B contributes to chromosome rigidity
and segregation by promoting the binding of condensin I
to chromatin. We have also addressed how Aurora B might
mediate the dissociation of cohesin from chromosome
arms.
