Enhancing the resolution of cohesin dynamics in meiosis

Graf, Peter (2018): Enhancing the resolution of cohesin dynamics in meiosis. Dissertation, LMU München: Fakultät für Biologie

Abstract

Meiosis is a specialized form of cell division in which one diploid mother cell is converted into four haploid daughter cells. Cohesin is a multi-protein complex, providing cohesion to replicated chromosomes. During meiosis, cohesin is removed from chromosomes in two steps. First, it is proteolytically cleaved from chromosome arms in anaphase I, whereas cohesin in the vicinity of the centromere is protected from cleavage. This pericentromeric cohesin is then removed in anaphase II. This stepwise loss of cohesin is part of the current model of meiotic chromosome segregation. Evidence for this kind of cohesin dynamics came originally from immunofluorescence experiments with very limited spatial resolution. A new workflow was established by combining a novel synchronization system for budding yeast meiosis with a calibrated and optimized ChIP-Seq protocol. This workflow allows resolving the cohesin dynamics in the course of the two meiotic divisions with unprecedented temporal and spatial resolution. With this new experimental system, we confirmed the existence of two cohesin fractions on chromosomes, a protected and an unprotected fraction. Contrary to the current model, we detected both fractions in the region around the centromere. This indicates that the distinction between arm cohesin and pericentromeric cohesin is not identical to the classification into unprotected cohesin and protected cohesin. These results suggest that the mechanism of protection is not only determined by the localization of the cohesin protein complex. Additionally, we discovered significant differences in the cohesin protection activity among individual chromosomes. The protein Sgo1 is required for the centromeric protection of cohesin. Sgo1 was analyzed directly with the new workflow, and we generated novel insights into the loading of the protection machinery onto chromosomes and the establishment of centromeric protection in meiosis. The protection machinery is loaded onto chromosomes in a cohesin-dependent mechanism, and a novel model of a dynamic three-step loading mechanism of the protection machinery is presented. This model explains how the cells are able to provide a robust and reliable protection to cohesin located in very diverse patterns on different chromosomes. Moreover, the model suggests a new function of the protein Sgo1 in centromeric protection. A last result is that the polo-like kinase of budding yeast, Cdc5, is involved in regulating the levels of the protection machinery, which are loaded onto chromosomes.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Keywords: Meiosis, Cohesin, Sgo1, Protection, ChIP-Seq
• Themengebiete: 500 Naturwissenschaften und Mathematik ; 500 Naturwissenschaften und Mathematik > 570 Biowissenschaften, Biologie
• Fakultäten: Fakultät für Biologie
• Sprache der Hochschulschrift: Englisch
• Datum der mündlichen Prüfung: 27. September 2018
• 1. Bericht­erstatter:in: Bramkamp, Marc