[Cross-fire over the nucleosome: molecular basis of post-meiotic male haploid genome compaction]

In mammals, the post-meiotic phases of spermatogenesis direct a drastic compaction of the genome characterized by the replacement of the majority of histones by small basic non-histone proteins, transition proteins followed by protamines. Although the mechanisms controlling this process are poorly understood, available data suggest that the nucleosome, which represents the universal unit of genome organization in eukaryotes, is the target of specific events cooperating to globally transform DNA organization at a genomic scale. Indeed, after meiosis, nearly all nucleosomes associated with the male genome undergo successive modifications increasing their instability, finally leading to their dissociation and re-organization. The characterization of the underlying mechanisms is a real challenge and appears as essential for the understanding of male gametogenesis and associated pathologies.