Preserving Genetic Integrity in Reproduction: Insights from Telomere Protection and Sperm Head-Tail Junctions

Abstract: This doctoral thesis embarks on a meticulous exploration of genetic integrity within the expansive domain of reproductive biology. Its overarching objective is to decipher the intricacies that underlie the preservation of hereditary stability across generations. This multifaceted inquiry transcends the mere conservation of telomere integrity and delves into the intricate roles played by sperm head-tail junctions. These elements are integral in orchestrating the precise management of genetic information throughout the complex journey of reproduction. Paper I: This thesis begins by investigating the integral role of the protein MC2 (Male germ cell-upregulated coiled-coil domain-containing protein 2) in anchoring sperm heads to their tails, a pro-cess crucial for maintaining the integrity of male germ cells during spermiogenesis. The role of MC2 dysfunction in male sterility is significant, particularly in the context of its involvement in the rigid assembly of the head-to-tail coupling apparatus (HTCA). Our findings indicate that in the absence of functional MC2 protein, the HTCA region becomes disconnected from the nucleus, specifically during the elongation phase of spermatids. This disconnection leads to the production of acephalic spermatozoa and results in male sterility. As we shift our focus from the defects in spermiogenesis that cause male infertility to the earlier stage of spermatogenesis, specifically meiosis, we further reinforce the theme of maintaining genetic integrity throughout the reproductive process. Paper II: Building upon this foundation, we delve into the meiosis-specific telomere protein TERB1 that anchors telomeres to the nuclear envelope and facilitates the pairing of homologous chromo-somes. We found that although TERB1 has an MYB-like DNA-binding domain, it doesn't have the typical DNA-binding activity. Furthermore, the MYB domain of TERB1 is not necessary for telomere localization, homologous pairing, or fertility, but it does regulate the enrichment of cohesin and promotes the remodeling of axial elements. This function of the TERB1 MYB domain is likely crucial for maintaining telomeric DNA and genomic integrity by preventing meiotic telomere erosion over long evolutionary timescales. Paper III: Shifting focus from the previous mouse animal model to the Caenorhabditis elegans model, we elucidate the roles of double-stranded telomeric DNA-binding proteins DTN-1 and DTN-2, which also have MYB-like DNA-binding domains, in ensuring germline immortality in C. elegans. C. elegans, with its short lifespan and amenability to in vivo experimentation, provides a valuable animal model for understanding the protection of genetic material across generations. Keywords: Reproductive biology, Sperm head-tail junctions, HTCA, Telomeric DNA-binding proteins, TERB1, MYB domain, DTN-1 and DTN-2