The sperm LINC complex: The LINK between chromatin integrity, sperm motility and male fertility

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During spermiogenesis, histone-to-protamine exchange is followed by chromatin hypercondensation representing a sperm quality control checkpoint, as incomplete histone replacement and/or aberrant protamine-1 (PRM1) to protamine-2 (PRM2) ratios are associated with male subfertility. Within the last years, sperm chromatin developed into an emerging field of reproductive medicine. We were able to demonstrate that PRM2-deficient male mice are infertile due to highly elevated levels of fragmented sperm DNA and completely immotile sperm (Schneider et al. 2016). This observation together with the facts that (1) a second mouse line lacking PRM1 has been generated and (2) sperm from subfertile men are known to exhibit an aberrant PRM1 to PRM2 ratio, represent the basis for the proposed DFG-GACR project, where both applicants join their expertise and pool their lab resources in order to study the signal transduction from chromatin to cytoskeleton (motility) in more detail. Applicants hypothesize that decreased (subfertile men, heterozygous mice) or missing (homozygous mice) protamine expression is followed by incomplete chromatin condensation finally resulting in a dysfunctional LINC (Linker of Nucleoskeleton and Cytoskeleton) network system due to aberrant histone post-translational modifications (PTMs) that prevent binding of chromatin to the INM and/or aberrant expression of LINC complex components impeding exchange of information between nucleoskeleton and cytoskeleton. Due to group-specific expertise and pre-work, the Steger group will focus on interactions between sperm chromatin and nuclear membrane, whereas the Hortova group will concentrate on interactions between nuclear membrane and sperm cytoskeleton. Firstly, differences in both localization and interaction of selected nuclear (protamines, modified histones) and cytoplasmic (actin filaments, microtubules) proteins with LINC complex proteins (LBR, SUN, KASH) between wild-type and protamine-deficient mice will be identified. Secondly, data obtained in mice will be compared with (sub)fertile men. This complex approach will increase our knowledge on the crosstalk between molecular factors involved in the pathophysiology of human subfertility associated with incorrect histone to protamine exchange. Applicants share common scientific interest, but exhibit different technical expertise perfectly complementing each other. The proposed project will be embedded in a highly stimulating scientific environment, as Steger maintain two DFG-funded projects with Prof. Schorle (Bonn, D), who generated the protamine-deficient mouse lines applying CRISPR/Cas9 technology, and Hortova holds a GACR-funded project studying protein-protein interaction in gametes. Expected results on protein-protein interactions involved in the nucleus-cytoplasm communication will contribute to new aspects of our understanding of molecular regulation mechanisms of chromatin integrity and sperm motility.