PSV-9 - Cold exposure impacts DNA methylation patterns of genes in cattle sperm involved in early embryonic and bone development

Abstract: DNA methylation and other epigenetic modifications are indispensable for maintaining sperm quality, fertilization capacity, and embryonic and postnatal development. In mice, environmental factors, such as stress, nutrition, or exposure to the cold condition, have been demonstrated as factors that alter methylation marks of sperm that are passed to the subsequent generation through transgenerational inheritance and genomic imprinting. Breeding bulls from northern regions of the USA are exposed to extreme cold for 2-3 months during the winter; however, no single study has analyzed the consequences of this cold exposure on the methylation pattern of bull sperm, which constitutes a significant knowledge gap. Therefore, this study aimed to explore the effects of cold exposure on the overall and gene-specific methylation status in sperm.

We collected semen from 5 bulls during winter seasons after cold exposure and at normal temperatures during late spring. Whole Genome Bisulfite Sequencing (WGBS) was conducted to obtain the DNA methylation profile of these semen samples and to identify unique genes that have differentially methylated regions due to cold exposure.

Cold exposure didn’t change the overall methylation level between the two groups but induced 438 Differentially methylated regions (DMRs) that overlapped with promoters, introns, exons, intergenic regions, shores, and shelves of CpG island (CGI) in 186 unique genes. We also identified nine unique differentially methylated genes (DMGs) (Pax6, Macf1, Mest, Ubqln1, Smg9, Trappc9, Ctnnb1, Lsm4, Peg10) involved in embryonic development and nine unique DMGs (Prmt6, Nipal1, C21h15orf40, Slc37a3, Fam210a, Raly, Rgs3, Lmbr1, Gan) involved in osteogenesis. DMRs were located in the promoter regions and introns of these genes which preferentially involve gene silencing and alternative splicing. Among the DMGs involved in embryonic development, Mest and Peg10 are two paternally imprinted genes where only the paternal allele expresses. Peg10, required for optimal placental growth and trophoblast proliferation, overlapped with a hypermethylated DMR in the promoter region. Mest, another paternally imprinted gene, the downregulation of which results in embryonic growth retardation, had hypermethylation in introns. Moreover, Methylation-specific PCR (MS-PCR) verified the methylation changes in the identified regions.

It was the first study to investigate the effect of cold exposure on DNA methylation of cattle sperm and suggest its association with altered sperm DNA methylation profiles. Differential methylation appears to alter gene expression and affect early embryonic development, osteogenic activity, and overall offspring growth performance through the imprinting effects.