Retained Acetylated Histone Four in Bull Sperm Associated With Fertility

Abstract

Bull fertility, ability of the sperm to fertilize and activate the egg and support embryo development, is vital for cattle reproduction and production. Even though majority of histones are replaced by protamines, some histones are retained in sperm. It is known that chromatin remodeling during spermatogenesis results in dynamic changes in sperm chromatin structure through post-translational modifications (PTM) of sperm histones, which are important for regulation of gene expression. However, amounts of sperm Histone 4 (H4), its acetylated form (H4 acetyl), and to what extent these molecular attributes influence sperm chromatin structure and bull fertility are unknown. These gaps in the knowledge base are important because they are preventing advances in the fundamental science of bovine male gamete and improvement of bull fertility. The objective of this study was to test the hypothesis that expression dynamics as well as PTM of sperm H4 are associated with bull fertility. Flow cytometry was utilized to quantify H4 and H4 acetylated form in sperm from seven high and seven low fertility Holstein bulls. The results indicated that the average number of cells with H4 or H4 acetyl expression in high and low fertility bull sperm were 34.6 ± 20.4, 1.88 ± 1.8, 15.2 ± 20.8, and 1.4 ± 1.2, respectively. However, the sperm enriched in both H4 and H4 acetyl were different between high and low fertility groups (3.5 ± 0.6; 1.8 ± 0.8; P = 0.043). The localization and detection of H4 and H4 acetylation were measured by immunocytochemistry which revealed that H4 and H4 acetylation were equally distributed in the sperm head of high and low fertility sires. Western blotting results confirmed the presence of the H4 and its acetylated form in the sperm. Bioinformatics studies demonstrated that H4 is highly conserved among mammalians, and have significant gene ontology on spermatogenesis, early embryo implantation, and sperm capacitation. The results are significant because it demonstrates the replacement of canonical histone H4 into modified H4 acetylation in sperm and regulate its dynamics which is crucial for bull fertility and reproductive biotechnology. These findings advance fundamental science of mammalian early development and reproductive biotechnology.

Parental Effects on Epigenetic Programming in Gametes and Embryos of Dairy Cows

“…In contrast, low planes of nutrition of young Holstein-Friesian bulls resulted in the retarded onset of puberty ( Byrne et al, 2018 ). Although epigenetic studies related to bull metabolic status is still missing, DNA methylation and histone modifications patterns were both reported to be associated with bull fertility ( Verma et al, 2015 ; Kropp et al, 2017 ; Kutchy et al, 2018 ; Capra et al, 2019 ; Ugur et al, 2019 ). Functional annotation of these alterations indicate that they might be involved in spermatogenesis and embryo development ( Verma et al, 2015 ; Ugur et al, 2019 ).…”

The epigenome of male germ cells and the programming of phenotypes in cattle

“…In addition, other sncRNAs such as tRF-Gly or tRF-Glu may represent another source of fertility biomarkers, as suggested by their differential expression according to in vitro fertilization outcomes in humans ( Hua et al, 2019 ). Due to the high compaction level of sperm chromatin, studies on the genomic location of posttranslational modifications of histones are technically challenging; however, the histone retention degree and associated modifications have been reported to vary as a function of bull fertility using flow cytometry ( Ugur et al, 2019 ).…”

Sperm Functional Genome Associated With Bull Fertility

“…The conception rate of each bull was plotted in a graph, and the standard deviation (SD) and the mean were calculated. The criterion for selecting high-fertile bulls was conception rate more than “mean + 1 or 2 SD,” while those below “mean – 1 or 2 SD” were considered as low-fertile bulls ( 5 , 6 ).…”