Heun lab paper featured in Cell Rep. Authors Image Centromeres are epigenetically identified by the histone-variant CENP-A. Using a heterologous system, Roure et al. investigate how Drosophila centromeres are maintained through cell generations and show that the chaperone CAL1 acts as a dynamic loading factor for dCENP-A and dCENP-C to sustain a self-propagating loop of epigenetic centromere inheritance. Roure, V., Bethan Medina-Pritchard, M., Lazou, V., Rago, L., Anselm, E., Venegas, D., Jeyaprakash, A.A., Heun, P. Summary of Paper by Lori Koch During cell division, DNA is packed into chromosomes that are then pulled into the new daughter cells. A protein complex called the kinetochore connects each chromosome to the dynamic fibers that provide the force to move them. The kinetochore forms at a single location on each chromosome called the centromere. If there are issues in the formation of centromeres or kinetochores, chromosomes may not be properly inherited by the new cells. When cells inherit the wrong number of chromosomes it can cause serious health issues such as cancer or developmental defects. Despite its importance, how centromeres are initially formed and propagated remains unclear, even after years of study. One thing that is clearly important is that a specialised histone protein called CENP-A must replace the histone protein H3 in the nucleosomes that wrap centromeric DNA. In the model organism Drosophila melanogaster (fruit fly), there is evidence that the protein CENP-C recruits the histone chaperone and CENP-A binding protein called CAL1 to the centromere. However, mechanistic details such as how CENP-C is initially recruited to the centromere were unknown. In their recent publication, members of the Heun Laboratory uncover the molecular requirements for CENP-A, CENP-C and CAL1 recruitment to centromeres. To do this, they performed molecular tethering experiments in which they transiently recruited fly proteins to specific regions of DNA in human cells and tested for the ability of a tethered protein to recruit the other fly proteins. Since there was no interaction between the fly and human centromere proteins in these cells, they were able to use this system to determine the order of de novo recruitment of the fly centromere proteins. Overall, they found that CAL1 is not only needed to incorporate CENP-A into chromatin, but also functions to recruit CENP-C to the centromere in the presence of CENP-A nucleosomes. By expressing all three fly proteins CENP-A, CAL1 and CENP-C in the human cells they found that CENP-A incorporation into chromatin could be kick-started by tethering CAL1 or CENP-C to a specific chromosome region. Interestingly, by adding a drug to disrupt the initial tethering, they could show that CENP-A nucleosomes where still inherited and reloaded in subsequent rounds of cell division. These data show that the CENP-A-CAL1-CENP-C module is sufficient to create a de novo centromere-like chromatin region that self-propagates even when the initial tethering is shut off. In the future, the lab aims to exploit this system to improve the function of centromeres on human artificial chromosomes that could become relevant in gene therapy strategies. Related links Journal Link DOI Heun Lab Website This article was published on 2024-06-17
