Histone variant H2A.L.2 guides transition protein - dependent protamine assembly in male germ cells. Mus musculus

Histone replacement by small basic proteins, transition proteins (TPs) and protamines (Prms) constitutes an essential step for the successful production of male gametes, yet nothing is known on the underlying functional interplay between histones, TPs and Prms. By studying spermatogenesis in the absence of H2A.L.2, a spermatid-specific histone variant, we identify a new step essential for the "metamorphosis" of nucleosomes to nucleoprotamines. H2A.L.2 plays the role of a "Trojan horse" histone, which induces dramatic structural changes that enables the invasion of nucleosomes by TPs, themselves driving the processing and incorporation of Prms. H2A.L.2 incorporation initiates a series of rapidly changing transitional states that ultimately shift to a more stable state characterized by nucleoprotamine assembly and histone-TP Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporationdisplacement, leading to the generation of mature spermatozoa. The textbook view of histone-to-nucleoprotein transition needs to be revisited to include a new step with H2A.L.2 assembly prior to the action of TPs and Prms. Overall design: MNase-seq analysis on WT and H2A.L.2-less mouse during three stages of spermiogenesis: Spermatocyte, Round Spermatid and Condensing Spermatid). MNase produces two distinct fragment size populations for condensing spermatid samples: nucleosome-like fragments (approximately 130 to 170 bp) and smaller structure fragments (approximately 40 to 80 bp). These populations are separated by electrophoresis prior to sequencing. The eight samples have been sequenced in three runs on Illumina NextSeq500 to achieve higher coverage. Runs for each sample are merged before downstream analysis and after quality control and alignment. Total read counts from all sequencing runs ranged from 207 to 753 million reads per sample.