Investigation of human testis-specific histone variant H2BFW

Abstract

In eukaryotic cells, the genomic DNA is wrapped into nucleosome structure with the help of histone octamer that contains two copies of H2A, H2B, H3, and H4). The histones themselves can be post-translationally modified and replaced during many metabolic processes. These dynamics play essential roles in transcription regulation, DNA damage repair, development, and many other processes. In spermatogenesis, canonical histones can be replaced by testis-specific histone variants, and one of these variants is H2BFW, which is only present in primates. Mutations or single-nucleotide polymorphisms (SNPs) of H2BFW are associated with male infertility and severe phenotype like azoospermia. However, the functional roles of H2BFW in spermatogenesis remain unclear. First, we identified that H2BFW was mainly expressed in the early stages of spermatogenesis (i.e., spermatogonium and primary spermatocyte); this is in stark contrast with TH2B, another testis-specific histone H2B variant, which was mainly expressed in the later stages of spermatogenesis including spermatid and spermatozoon. Biochemical studies showed that H2BFW-containing nucleosomes are less stable than H2B nucleosomes. With single-molecule optical tweezers assays, we demonstrated that H2A/H2BFW dimer has a weaker interaction with nucleosomal DNA than their canonical counterpart. H2BFW significantly reduces the free energy cost of the DNA histone dimer interaction. Besides, the communication between H2A/H2BFW and H3/H4 tetramer is also weaker than that in the H2B nucleosome. Moreover, H2BFW nucleosome lowers the barrier for RNA polymerase II (RNAPII) to transcribe through the nucleosome by reducing the pausing of RNAPII. Chromatin immunoprecipitation (ChIP) sequencing data showed that H2BFW was enriched around some gene markers of spermatogenesis and transcription factors. Taken together, our results suggest that H2BFW may enhance transcription of spermatogenesis-related genes in early spermatogenesis. Keywords: Histone Variants, H2BFW, Optical Tweezers, Spermatogenesis

Date of Award	2020
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology