Roles of condensin complexes in the maintenance and functional expression of genome

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In higher eukaryotic cells, there exist two condensin complexes, known as condensin I and II. Both play essential yet distinct functions in the processes of mitotic chromosome assembly and segregation. In this study, we have investigated chromosomal aberrations caused by the defect of chromosome assembly and segregation. Further, potential factors that might contribute to the distinct dynamics of condensin I and II have been searched.(1) We found that clinical cytogenetic chromosome preparations is not useful for defection of chromosomal defects associated with chromosome assembly and segregation. On the other hand, combination of condensin-depletion and replicative stress caused severe morphological defects in mitotic chromosomes of Hela cells. These results suggest that condensin may play a role in protection or maintenance of chromosomal structure in addition to chromatin assembly. Moreover, unknown factor (s) might contribute to the formation of chromosome morphology.(2) We have established a new a cytological method, terms monopolar preparation, for clinical analysis of human diseases associated with defects of chromosome assembly and segregation.(3) We have found that condensins I and II tend to be enriched in R-band and G-band regions, respectively, on metaphase chromosomes. Further, condensin distribution pattern also seems to be related with histone modifications.(4) We demonstrated that condensin II may bind to chromatin during S-phase in HeLa cells. This obsevation allows us to propose the working hypothesis that condensin II may play a role in coordinating two distinct chromosome events, i., e., DNA replication in S phase and chromosome assembly in M phase.