Biochemical and biophysical characterisation of human meiotic cohesin complexes

The cohesin complex is an essential component of mitotic and meiotic chromosomes due to its ability to control the topology of DNA. The core cohesin complex is a ring-like structure composed of two structural maintenance of chromosome proteins plus a kleisin that recruits additional subunits that control the loading and activity of cohesin on DNA. Recent single-molecule approaches show that cohesin displays two primary activities in vitro: ATP-dependent DNA translocation, leading to the formation of DNA loops, and topological entrapment of two DNA molecules, which can explain sister chromatid cohesion. These experiments used cohesin complexes containing the mitotic kleisisin RAD21, but higher eukaryotes express meiosis-specific kleisins, including RAD21L and REC8 in mammals, that are essential for fertility. Although in vivo experiments in mouse and C. elegans suggest that REC8 and RAD21L complexes display functional specialisation, the molecular activity of these complexes remains unknown. The goal of this project is to perform a biochemical and biophysical characterisation of human cohesin complexes containing the REC8 and RAD21L kleisins. To this end, I will combine bulk biochemical approaches with single-molecule methods (TIRF microscopy, optical tweezers) to determine the ATPase activity, complex formation with cohesin regulators (SA3, PDS5, NIPBL), topological DNA entrapment, and loop formation activity of human REC8 and RAD21L complexes. This project will provide mechanistic insights into the mechanisms that ensure fertility in humans.