Mechanisms of Transgenerational Centromere Inheritance

Centromeres control genetic inheritance by directing chromosome segregation, but centromeres in most species are not genetically encoded. Instead, centromeres are specified epigenetically by the presence of Centromere Protein A (CENP-A), a histone H3 variant which replaces canonical histone H3 in centromeric nucleosomes. This dissertation describes underlying mechanisms governing CENP-A nucleosome transmission and epigenetic centromere inheritance during the cell cycle. In the first part of this dissertation, I discuss the role of the CENP-A nucleosome binding protein CENP-C in stabilizing CENP-A nucleosomes at the centromere. Our work demonstrates that CENP-C both reshapes the histone core of the nucleosome, and that CENP-C depletion leads to the rapid removal of CENP-A from centromeres. These data indicate that CENP-C is necessary for stable retention of CENP-A nucleosomes at the centromere, and highlight molecular requirements of maintaining and transmitting centromere identity. In the second part, I describe the mechanism by which centromeres are inherited through the mammalian female germline. In cycling somatic cells, CENP-A is maintained by a cell cycle-coupled pathway, and there is no known mechanism to assemble new CENP-A nucleosomes outside of the G1-phase of the cell cycle. This epigenetic mechanism raises the question of how centromere identity is maintained during the extended prophase I arrest in mammalian oocytes. Using mice I generated, in which the Cenpa locus is conditionally inactivated in oocytes early in prophase I arrest, I tested whether centromere inheritance depends on a specialized meiotic loading pathway or on long-term retention of CENP-A nucleosomes loaded prior to prophase I arrest. We find that CENP-A nucleosomes are stably retained at centromeres for 12 months with no detectable contribution from meiotic loading. Our results show that CENP-A which is loaded before birth, prior to prophase I arrest, is fully functional 12 months later, indicating that stable retention of CENP-A nucleosomes underpins centromere inheritance through the female germline. Finally, I discuss my efforts to create a mouse model to study centromere inheritance in the mammalian male germline. Together, the data presented in this dissertation greatly enhance our understanding of the molecular mechanisms that contribute to transgenerational centromere inheritance