Imprinting of mammalian male gametes is gene specific and does not occur at a single stage of differentiation

Abstract

Epigenetic modifications such as DNA methylation and alterations to chromatin structure have been proposed as hallmarks of imprinting in somatic cells after fertilization. In the germ cell line, gene imprinting needs to be reset in order to transmit the correct sex-specific imprinting pattern to the next generation. The precise timing of imprint erasure and re-establishment for many genes remains to be determined and precise molecular mechanisms of genomic imprinting have not yet been fully characterized. Here, we have analysed the methylation state and DNase-I sensitivity of two genes with reciprocal genomic imprinting (U2af1-rs1 and H19 genes) in a male mouse primordial germ cell (PGC) derived cell line (EG-1), isolated post-natal spermatogonia and mature sperm cells. Our results show that establishment of imprinting of the U2af1-rs1 and H19 genes during male germ cell differentiation occurs at different stages of differentiation. Furthermore, the presence of DNase-I hypersensitive sites may constitute a molecular marker to identify alleles and subsequently acquire the appropriate methylation imprint. We propose that this molecular identifier may be present or absent for a specific gene according to the sex of the gamete.

Epigenetic disturbances in in vitro cultured gametes and embryos: implications for human assisted reproduction

“…Sex-specific methylation patterns are then established during germ-cell differentiation (6,13). In the male mouse germline, remethylation is initiated after prenatal mitotic arrest in prospermatogonia and proceeds in a gene-specific manner until the end of the pachytene spermatocyte stage (14)(15)(16)(17)(18). In the female germline, methylation patterns also are established in a gene-specific manner; however, this occurs during later stages of oocyte development (19)(20)(21)(22).…”

Broad DNA methylation changes of spermatogenesis, inflammation and immune response‐related genes in a subgroup of sperm samples for assisted reproduction

“…The sperm-specific methylation patterns are then established during germ cell differentiation (Hajkova et al ., 2002; Carrell, 2012). Remethylation is initiated after prenatal mitotic arrest in prospermatogonia and proceeds in a gene-specific manner until the end of the pachytene spermatocyte stage (Rousseaux et al ., 2005; Oakes et al ., 2007; Boyano et al ., 2008). Whole genome bisulfite sequencing revealed that the promoter regions of most developmentally important genes are hypomethylated in spermatozoa (Hammoud et al ., 2009), most likely to ensure their rapid activation in the early embryo.…”

Hypothesis: gonadal temperature influences sex-specific imprinting

“…In fact, it is commonly accepted that the establishment of maternally methylated DMRs occurs after birth in females, simultaneously, in the oocytes at the growing oocyte stage (Lucifero et al, 2004; Morgan et al, 2005; Ferguson-Smith, 2011; Smith and Meissner, 2013). In males there is evidence that de novo methylation starts late in fetal life or during the newborn period, and at least for some loci and some species, it seems to be acquired during post-natal life (Davis et al, 1999; Kerjean et al, 2000; Lucifero et al, 2004; Morgan et al, 2005; Boyano et al, 2008; Smith and Meissner, 2013; Suzuki et al, 2013). Boyano et al (2008) have observed that genomic imprinting of H19 genes is established at different stages of germ cells differentiation during post-natal life in male mice.…”

“…In males there is evidence that de novo methylation starts late in fetal life or during the newborn period, and at least for some loci and some species, it seems to be acquired during post-natal life (Davis et al, 1999; Kerjean et al, 2000; Lucifero et al, 2004; Morgan et al, 2005; Boyano et al, 2008; Smith and Meissner, 2013; Suzuki et al, 2013). Boyano et al (2008) have observed that genomic imprinting of H19 genes is established at different stages of germ cells differentiation during post-natal life in male mice. Likewise, Suzuki et al (2013) have reported that the H19 DMR undergoes de novo methylation only after 34 days post-partum in the germ line of the marsupial Tammar Wallaby .…”