Epigenetic trajectory of male meiosis

Male meiosis is the developmental process in which germ cells halve their chromosome number while continuing toward sperm formation. This review focuses on mechanistic studies of male meiosis in mouse and develops an epigenetic framework for this transition, centered on two key concepts. First, the foundation of meiosis is established ahead of meiotic entry. Prior to meiosis, germ-cell genes are poised and chromosomes are organized to support the upcoming meiotic program. Stage-specific signals and transcription factors then act on this prepared state to initiate meiotic gene expression. Second, meiosis reorganizes the germline in preparation for the post-meiotic spermiogenic program. In early prophase, nascent transcription remains low, allowing chromosomes to reorganize for recombination. Later, pachytene spermatocytes undergo an autosomal transcriptomic burst required for meiotic progression and post-meiotic development, while retrotransposon expression is controlled and unsynapsed sex chromosomes are silenced. Together, these concepts frame male meiosis as both the execution of a prepared developmental process and a critical window during which the germline genome is reshaped. This epigenetic trajectory connects gene regulation, chromosome organization, genome defense, and developmental timing to ensure production of functional sperm.