Aging‐associated reduction of chromosomal histones in mammalian oocytes

Mammalian oocytes undergo a long‐term meiotic arrest that can last for almost the entire reproductive lifespan. This arrest occurs after DNA replication and is prolonged with age, which poses a challenge to oocytes in maintaining replication‐dependent chromosomal proteins required for the completion of meiosis. In this study, we show that chromosomal histones are reduced with age in mouse oocytes. Both types of histone H3 variants, replication‐dependent H3.1/H3.2 and replication‐independent H3.3, decrease with age. Aging‐associated histone reduction is associated with transcriptomic features that are caused by genetic depletion of histone H3.3. Neither the genetic reduction of chromosomal H3.1/H3.2 nor H3.3 accelerates the aging‐associated increase in premature chromosome separation that causes meiotic segregation errors. We suggest that aging‐associated reduction of chromosomal histones is linked to several transcriptomic abnormalities but does not significantly contribute to errors in meiotic chromosome segregation during the reproductive lifespan of mice. Mammalian oocytes undergo a long‐term cell cycle arrest following premeiotic DNA replication. This study shows that chromosomal histones, including replication‐dependent H3.1/H3.2 and replication‐independent H3.3, decrease with age.