Impact of seasonality, storage of semen, and sperm head‐shape on whole tissue methylation and expression of methylation responsive candidate genes in swine placenta and fetal livers from summer and winter breedings

Abstract

Epigenetics includes the study of external factors that can influence the expression of genes by altering the accessibility of DNA through methylation. To investigate the epigenetic influence of season, sperm head shape, and semen storage on placental and fetal tissues, pregnancies were generated in the summer or winter using boar semen from either least or most sperm head shape change, collected during cool or warm seasons, and stored as cooled‐extended or cryopreserved. The lowest (p < 0.05) ratios of 5‐methylcytosine to 5‐hydroxymethylcytosine activity (5mC:5hmC) in fetal liver were from summer breedings and in placental tissues from winter breedings. The relative expression of placental CDH1 tended ( p < 0.10) to be greater in placenta generated from cryopreserved semen or semen collected during cool periods. The relative expression of placental GNAS was affected ( p < 0.05) by the interaction of breeding and semen collection seasons. Cryopreserved semen increased ( p < 0.05) the placental relative expression of GNAS. Placental MEST and RHOBTB3 tended ( p < 0.10) to have a greater relative expression from pregnancies generated using semen collected during cool periods used during winter breedings. Within fetal liver, the relative expression of GNAS and HGF was greater ( p < 0.05) from winter breedings. Interaction of winter breedings and least sperm head shape change tended ( p < 0.10) to have the greatest fetal liver expression of CDH1. Seasonality of semen collection, breeding, and the effect on sperm head shape change had an influence on the expression of genes with known differentially methylated regions or response to methylation activity from embryonic and extraembryonic tissues.

Genes Associated With Chromatin Modification Within the Swine Placenta Are Differentially Expressed Due to Factors Associated With Season

“…External stimuli, both maternal and paternal, have been shown to alter the placental epigenome in multiple species ( Deshpande and Balasinor, 2018 ). We have previously shown altered global methylation activity in the placenta derived from semen collected in cool or warm season and stored as cooled-extended or cryopreserved and then used to inseminate gilts in summer or winter ( Rempel et al, 2019 ). Briefly, placenta derived from winter breedings had reduced 5mC:5hmC activity.…”

“…Briefly, placenta derived from winter breedings had reduced 5mC:5hmC activity. Additionally, differences were detected in placental expression of genes with differentially methylated regions or genes responsive to methylation status due to semen collection, semen storage traits, and breeding season ( Rempel et al, 2019 ). In the current study, we used an epigenetic chromatin modifier RT 2 profiler array to determine regulatory epigenetic components in swine placenta that were altered by breeding season or semen characteristics.…”

“…Detailed description of gilt care and pregnancy generation were reported ( Rempel et al, 2019 ). Briefly, gilts had previously expressed signs of estrous and were at least 220 days of age at the time of a single-dose insemination following an established altrenogest and chorionic gonadotropin synchronization protocol.…”

“…The RQ values for the significant transcripts were evaluated for linear relationship with the previously reported global methylation activity (5mC:5hmC) in the placenta ( Rempel et al, 2019 ) using the Pearson correlation analysis in SAS.…”

“…Alteration in placental methylation patterns has been associated with impaired fetal growth and early pregnancy loss in humans ( Koukoura et al, 2012 ; Yin et al, 2012 ). Previously, we have shown differences in placental DNA methylation activity and expression of genes with differentially methylated regions in pregnancies derived from semen collected in cool or warm periods, stored as cooled-extended or cryopreserved, and breeding gilts in summer or winter ( Rempel et al, 2019 ). Specifically, swine placentas derived from winter breedings yielded reduced 5-methylcytosine:5-hydroxymethylcytosine (5mC:5hmC), potentially “loosening” the chromatin structure allowing the transcription of methylation-responsive genes, such as MEST and RHOBTB3 ( Rempel et al, 2019 ).…”