Endocrine Abstracts

Background: Fetal glucocorticoid overexposure is associated with low birthweight and increased cardiovascular disease risk in the offspring. Such ‘programmed effects’ can be transmitted across generations through both male and female lines. Disruption of a germline epigenetic reprogramming pathway, characterised by genome-wide erasure and subsequent re-establishment of DNA methylation, may underpin the intergenerational transmission of programmed effects. We used a rat model to explore the hypothesis that glucocorticoid overexposure affects DNA re-methylation in germ cells in late gestation.

Methods: Pregnant female Wistar rats were treated with dexamethasone (Dex:100 μg/kg per day) or vehicle from E15.5 onwards. Testes were collected between E18.5 and E21.5, and immunofluorescence used to localise the glucocorticoid receptor (GR), 5-methylcytosine (5 mC) and the DNA methyltransferases DNMT3a, 3b and 3L. To explore whether Dex affected testis maturation we assayed for the presence of the double-sex and mab-3 related transcription factor 1 (DMRT1), an important transcription factor in early testicular differentiation, which is undetectable in germ cells after E19.5.

Results: GR was detectable in germ cells throughout the time course. Dex treatment was associated with a greater number of 5 mC positive germ cells at E19.5 but this difference was no longer apparent at E20.5. DNMT3a, 3b and 3L were detected in germ cells throughout the re-methylation phase in both treatment and control groups. DMRT1 was present in germ cells at E18.5 and E19.5, and absent by E20.5 in both groups, suggesting that the shift in the timing of re-methylation may not correspond to premature maturation across the entire testis.

Conclusions: Our observations suggest that Dex exposure is associated with earlier germ cell re-methylation in the absence of global changes in the DNMTs. The mechanism(s) mediating this change remain to be elucidated.