Sperm heterogeneity and DNMT/TET activities do not account for sperm DNA methylation changes observed in the epididymis

Following their production in the testis, spermatozoa enter the epididymis to gain their motility and fertilizing abilities. This post-testicular maturation coincides with sperm epigenetic profile changes that influence the progeny outcome. While recent studies underscored the dynamics of small non-coding RNAs in the maturing spermatozoa, little is known regarding sperm methylation changes and their impact at the post-fertilization level. To map out the sperm methylome dynamics, we purified spermatozoa by FACS from the testis and the different epididymal segments (i.e. caput, corpus and cauda) of CAG/su9-DsRed2; Acr3-EGFP transgenic mice. Reduced-Representation Bisulfite Sequencing (RRBS-Seq) performed on DNA from these respective sperm populations indicated that high methylation changes were observed between spermatozoa from the caput vs. testis with 5546 entries meeting our threshold values (q value < 0.01, methylation difference above 25 %). Most of these changes were transitory during epididymal sperm maturation according to the low number of entries identified between spermatozoa from cauda vs. testis. Overall design: DNA methylation profile of isolated sperm from testis, caput, corpus, and cauda