Methylation levels at the GNAS locus is not associated with field fertility in Holstein bulls
Résumé
Prediction of male fertility remains a major goal to promote animal insemination (AI). The combination of several markers of sperm quality provides promising results but remain still unsatisfactory. The crucial role of epigenetics in sperm functions and fertilization efficiency is now recognized. A better understanding of epigenetic mechanisms such as DNA methylation may highlight new key criteria that could improve prediction models. Recently, an increased methylation level at the imprinted Gnas locus has been observed in infertile boars (Congras et al., 2014). Our study evaluated the relationship between CpG methylation status at this locus and the field fertility (SF) score of Holstein bulls. Firstly, 56 CpG positions of GNAS locus were analyzed by bisulfite conversion and pyrosequencing using gDNA from 25 Holstein bulls. A negative correlation was observed between SF and methylation status. The two most informative CpG were selected for further investigation using an extended cohort (113 bulls; SF mean=-1.6±7.0 [-30 to +7.5]). Low methylation levels were observed (CpG#1: 26.7±3.4%; CpG#2: 14.4±2.4%). High variability between bulls (min/max %: 18.3/34.4 and 9.7/20.8) and bull families was noted (e.g. mean CpG#1 methylation percentage inner bull families ranging from 21.3±0.2% to 32.3±1.9%), suggesting that the genetic background may affect the methylation status. However, the correlation between SF and the methylation level was lossed. More studies will probably be required to explore the link between the GNAS methylation variability and fertility efficiency or embryo developmen. In conclusion, the methylation status at the Gnas locus does not provide accurate information to improve fertility prediction models. However, our results pave the way to study the relationship between genetics and methylation status at specific or genome-wide levels (ANR SeQuaMol).