title: Dynamic changes in DNA modification states during late gestation male germ line development in the rat.
abstract: BACKGROUND
  Epigenetic reprogramming of fetal germ cells involves the genome-wide erasure and subsequent re-establishment of DNA methylation. Mouse studies indicate that DNA demethylation may be initiated at embryonic day (e) 8 and completed between e11.5 and e12.5. In the male germline, DNA remethylation begins around e15 and continues for the remainder of gestation whilst this process occurs postnatally in female germ cells. Although 5-methylcytosine (5mC) dynamics have been extensively characterised, a role for the more recently described DNA modifications (5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC) and 5-carboxylcytosine (5caC)) remains unclear. Moreover, the extent to which the developmental dynamics of 5mC reprogramming is conserved across species remains largely undetermined. Here, we sought to describe this process during late gestation in the male rat.
  
  
  RESULTS
  Using immunofluorescence, we demonstrate that 5mC is re-established between e18.5 and e21.5 in the rat, subsequent to loss of 5hmC, 5fC and 5caC, which are present in germ cells between e14.5 and e16.5. All of the evaluated DNA methyl forms were expressed in testicular somatic cells throughout late gestation. 5fC and 5caC can potentially be excised through Thymine DNA Glycosylase (TDG) and repaired by the base excision repair (BER) pathway, implicating 5mC oxidation in active DNA demethylation. In support of this potential mechanism, we show that TDG expression is coincident with the presence of 5hmC, 5fC and 5caC in male germ cell development.
  
  
  CONCLUSIONS
  The developmental dependent changes in germ cell DNA methylation patterns suggest that they are linked with key stages of male rat germline progression.
authors.affiliation: Endocrinology Unit, University/BHF Centre for Cardiovascular Science, University of Edinburgh, The Queen's Medical Research Institute, 47 Little France Crescent, Edinburgh EH16 4TJ, UK.
authors.forename: Catherine M
authors.initials: CM
authors.lastname: Rose
authors.affiliation: MRC Centre for Reproductive Health, University of Edinburgh, The Queen's Medical Research Institute, 47 Little France Crescent, Edinburgh EH16 4TJ, UK.
authors.forename: Sander
authors.initials: S
authors.lastname: van den Driesche
authors.affiliation: MRC Centre for Reproductive Health, University of Edinburgh, The Queen's Medical Research Institute, 47 Little France Crescent, Edinburgh EH16 4TJ, UK.
authors.forename: Richard M
authors.initials: RM
authors.lastname: Sharpe
authors.affiliation: MRC Human Genetics Unit, IGMM, Western General Hospital, Crewe Road, Edinburgh EH4 2XU, UK.
authors.forename: Richard R
authors.initials: RR
authors.lastname: Meehan
authors.affiliation: Endocrinology Unit, University/BHF Centre for Cardiovascular Science, University of Edinburgh, The Queen's Medical Research Institute, 47 Little France Crescent, Edinburgh EH16 4TJ, UK.
authors.forename: Amanda J
authors.initials: AJ
authors.lastname: Drake
keywords: 5-carboxylcytosine; 5-formylcytosine; 5-hydroxymethylcytosine; 5-methylcytosine; DNA modification; Germ cells; Rat; Thymine DNA Glycosylase