Single nucleotide polymorphism at 5′ UTR of H2BC1 and promoter methylation influence TSH2B expression

The transition from histones to protamines during spermiogenesis plays a crucial role in shaping the male epigenome, and any changes in this process can impact fertilisation potential and the ability of sperm to support early embryogenesis. In our previous research, we observed reduced levels of TSH2B in the sperm of infertile men with oligozoospermia and oligoasthenozoospermia. However, the regulatory mechanisms of the H2BC1 gene, which encodes TSH2B, in the testes are not yet understood. In this study, we investigated whether H2BC1 expression is influenced by SNPs in the 5' untranslated region (5' UTR) and promoter methylation. Luciferase assays were performed to assess the impact of 5' UTR variants in vitro and pyrosequencing was done to evaluate promoter methylation of the H2BC1 gene in the sperm of fertile and infertile men. Our findings suggest that the 5' UTR variants rs4711096 (c.-83A>G) and rs4712959 (c.-80C>T) positively regulate H2BC1 expression. Methylation analysis indicates hypermethylation of CpG sites, particularly at CpGs 2, 3 and 9 in H2BC1, can influence H2BC1 expression. This study offers new insights into the regulation of testis-specific genes.