THESIS
2020
x, 107 pages : illustrations (chiefly color) ; 30 cm
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...[
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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
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