I love chromosomes. I am always in awe when I see these little things that are chock full of information and instructions for a cell, and in turn, a whole organism. When I think about how finely-tuned the dance is that allows chromosome segregation to happen correctly every time during mitosis, I am beyond impressed. Today’s image is from a paper describing how sister chromatids become bound to one another.
Sister chromatids remain held together until anaphase segregates them into two future daughter cells during mitosis. Chromatid cohesion is mediated by the cohesin complex of proteins and is established long before mitosis. A recent study identified the role of a protein called XEco2 in acetylating a cohesin complex member called Smc3, a step that is required for the establishment of chromatid cohesion. In addition, Higashi and colleagues found that this role of XEco2 is important prior to DNA replication, requiring the formation of the pre-replication complex. Later, DNA replication serves to stabilize cohesion between sister chromatids. In the images above, sister chromatids are bound together in control cells and in cells depleted of XEco1 (left two columns). In cell depleted of XEco2, XEco1 and XEco2 together, or cohesin (middle and right two columns), sister chromatids are not bound tightly to one another.
Higashi TL, Ikeda M, Tanaka H, Nakagawa T, Bando M, Shirahige K, Kubota Y, Takisawa H, Masukata H, & Takahashi TS (2012). The Prereplication Complex Recruits XEco2 to Chromatin to Promote Cohesin Acetylation in Xenopus Egg Extracts. Current biology : CB, 22 (11), 977-88 PMID: 22560615