Abstract
BackgroundSperm epigenetics is an emerging area of study supported by observations reporting that abnormal sperm DNA methylation patterns are associated with infertility. Here, we explore cytosine-guanine dinucleotides (CpGs) methylation in high (HM) and low motile (LM) Bos taurus sperm populations separated by Percoll gradient. HM and LM methylation patterns were investigated by bisulfite sequencing.ResultsComparison between HM and LM sperm populations revealed that methylation variation affects genes involved in chromatin organization. CpG Islands (CGIs), were highly remodelled. A high proportion of CGIs was found to be methylated at low/intermediate level (20–60%) and associated to the repetitive element BTSAT4 satellite. The low/intermediate level of methylation in BTSAT4 was stably maintained in pericentric regions of chromosomes. BTSAT4 was hypomethylated in HM sperm populations.ConclusionsThe characterization of the epigenome in HM and LM Bos taurus sperm populations provides a first step towards the understanding of the effect of methylation on sperm fertility. Methylation variation observed in HM and LM populations in genes associated to DNA structure remodelling as well as in a repetitive element in pericentric regions suggests that maintenance of chromosome structure through epigenetic regulation is probably crucial for correct sperm functionality.
Highlights
Sperm epigenetics is an emerging area of study supported by observations reporting that abnormal sperm DNA methylation patterns are associated with infertility
Isolation of spermatozoa and evaluation of sperm characteristics Sperm cells were successfully fractionated into high motile (HM) and low motile (LM) populations; a significant (P < 0.05) improvement of several sperm quality parameters was observed in HM population in comparison to semen at thawing considering the following parameters: straight-line velocity Straight-line velocity (VSL), curvilinear velocity Curvilinear velocity (VCL), average path velocity Average path velocity (VAP) and amplitude of lateral head displacement Amplitude of lateral head displacement (ALH) variables [VSL: 46.08 ± 4.11, 61.24 ± 2.91; VCL: 76.35 ± 6.02, 110.37 ± 4.25; VAP: 55.38 ± 4.27, 74.02 ± 3.01; ALH 2.53 ± 0.14, 3.72 ± 0.10; respectively in semen at thawing and HM population (Additional file 1)
Bisulfite sequencing was applied to the methylationenriched genomic fraction to investigate Cytosine-guanine dinucleotides (CpGs) methylation level at single base resolution in the highly methylated regions
Summary
Sperm epigenetics is an emerging area of study supported by observations reporting that abnormal sperm DNA methylation patterns are associated with infertility. The genetic basis of male infertility accounts for about 15% of infertile cases [1, 2]. The etiology of this disorder remains unclear both in. DNA methylation of the 5-carbon position in cytosine residues was reported to be predominantly present in cytosine-guanine dinucleotides (CpG) and especially in GC rich regions called CpG islands (CGIs) [10]. Methylation is observed in Repetitive Elements (RE) of adult cells playing a role in the maintenance of chromosome structure and genome integrity [12]
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