On the other hand, it also increases cyclic AMP levels via a Gs-coupled pathway

for counteracting Aurora B activity to promote NER. NE, nuclear envelope. 6 Kitagawa and Lee CPC regulation in mitotic exit recruited to chromatin. In HeLa cells, RNAi against Aurora B or treatment with the Aurora B inhibitor hesperadin causes a loss of chromatin association of condensin I, but not condensin II. Maximal compaction of anaphase chromosomes in rat kidney cells also requires Aurora B. The association of condensin I to chromatin is also reduced after immunodepletion of Aurora B from Xenopus egg extracts. In S. pombe, Aurora B-like kinase Ark1 phosphorylates the kleisin protein Cnd2 of condensin throughout mitosis. Phosphorylation of the human Cdn2 homolog CAP-H by Aurora B promotes efficient association of condensin I, but not condensin II, to mitotic chromosomes in mammalian cells. Aurora Bdependent phosphorylation of Cnd2 promotes its association with histone H2A and H2A.Z. The conservation of PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19812545 phosphorylation-dependent condensin interactions with histone H2A variants in S. pombe and mammalian cells suggests that it is a fundamental mechanism shared in all eukaryotes. Together, it is clear that the CPC plays a critical role in promoting chromosome condensation for mitotic entry. The role of CPC relocation in coordinating proper anaphase chromosome segregation with decondensation In contrast to the mechanism of chromatin condensation, little is known about what controls chromatin decondensation after the exit from mitosis and in the early G1 phase. In S. cerevisiae, Cdc14 phosphatase activity impairs the association of the Cnd2 homolog Brn1 with chromatin, suggesting that condensin dephosphorylation by Cdc14 promotes chromosome decondensation at mitotic exit. Consistent with this idea, in mammalian cells, PP2A dephosphorylates the CAP-H2 subunit of condensin II during anaphase. PP1 also promotes chromosome decondensation because the disruption of mitotic chromosomes in DT40 cells with a conditional knockout of SMC2 of the condensin complex during anaphase can be overcome if Repo-Man is prevented from targeting PP1 to chromosomes. Because phosphorylation generally appears to stimulate the biochemical activity of the condensin complex, such as DNA binding and supercoiling, whether its dephosphorylation may reverse these effects to permit chromosome decondensation as cells return to interphase needs to be investigated. In this sense, relocating the CPC from the anaphase chromosome arm to the cell equator is likely important for efficient chromosome decondensation, not only by reversing Aurora B phosphorylation of condensin by PP1 but also by preventing Aurora B re-phosphorylation of condensin on anaphase chromosomes. However, this process of decondensation must occur in a tightly regulatory manner because partitioning of anaphase chromosomes to the opposite spindle poles requires sister chromatids to be condensed enough to allow their segregation away from the ingressing cleavage furrow. get INK1117 Moreover, the central spindle must also elongate enough to segregate even the longest chromosomes before chromosome decondensation occurs. Interestingly, the deposition of condensin onto chromosome arms reaches a peak during anaphase when the CPC relocates from anaphase chromosomes to the spindle midzone. During anaphase, an Aurora B phosphorylation gradient is thought to be centered at the spindle midzone and Aurora B phosphorylation of condensin keeps the segregating chromosomes apart during telophase . An Aurora B phosphorylation gradient e