| Abstract: | In addition to the role in the spindle apparatus and associated motors, the chromosome themselves play an important role in facilitating chromosome segregation. Sister chromatids are joined at the centromere through a protein complex called cohesin. Chromatids separation requires the degradation by separase of specific proteins acting as a glue to form the cohesin complex. This evolutionally complex is required for the establishment and maintenance of sister chromatids in a ring like structure. It is therefore a key question whether cohesin is indeed a main component of active centromere. Cohesin is insufficient to resist the splitting force exerted by microtubules until anaphase and must be renforced by cohesion provided by flanking DNA. The ring model suggests that cohesine might possess a considerable mobility when associated with chromatin. Observations demonstrate that the interior region of the centromere behaves as an elastic element. Chromosomes display remarkable elasticity, returning to their initial shape after being extended by up to 10 times. For larger deformations the thick filament is converted in thin filament which can be stretched six times before breaking. This article suggests an additional and novel role for the protein titin on chromosome structure and dynamic. Titine was identified as a chromosomal component and it was hypothesised that titin may provide elasticity to chromosome and resistance to chromosome breakages during mitosis. The elastic properties of purified titin correspond well to the elastic properties of chromosome in living cells. The deformability and bending rigidity are consistent with a model developed for titin elasticity. The association of the presence of cohesine ring and the activity of titin could be necessary for segregation. |
