Prenatal overexposure to the synthetic glucocorticoid dexamethasone (Dex) in rats reduces birthweight in the first generation (F1) and second generation (F2), including through the male line. We hypothesised that the mechanism for this would likely be epigentic perturbations in the male germline. DNA methylation profiling of F1 male germ cells at E19.5 and small RNA expression and Chromatin Immunoprecipitation (ChIP) sequencing for H3K4me1, H3K4me3, H3K27me3 and H3K9me3 on F1 sperm were used to test this hypothesis. No differences in DNA methylation, histone modifications or small RNA expression were observed, suggesting non-epigentic mechanisms may be responsible for the transmission of programmed effects in this model.. Transmission of glucocorticoid-programmed effects occurs without detectable changes in the germline epigenome

Background. Early life exposure to adverse environments affects cardiovascular and metabolic systems in the offspring. These “programmed effects” are transmissible to a second generation through both male and female lines, suggesting germline transmission. We have previously shown that prenatal overexposure to the synthetic glucocorticoid dexamethasone (Dex) in rats reduces birthweight in the first generation (F1) a phenotype which is transmitted to a second generation (F2), particularly through the male line. We hypothesised that Dex exposure affects developing germ cells, resulting in transmissible alterations in DNA methylation, histone marks and/or small RNA in the male germline. Results. We profiled epigenetic marks in sperm from F1 Sprague Dawley rats expressing a germ cell specific GFP transgene following Dex or Vehicle treatment of the mothers, using methylated DNA immunoprecipitation sequencing, small RNA sequencing and Chromatin Immunoprecipitation sequencing for H3K4me3, H3K4me1, H3K27me3 and H3K9me3. Although effects on birthweight were transmitted to the F2 generation through the male line, there were no detectable differences in DNA methylation, histone modifications or small RNA between germ cells and sperm from Dex-exposed animals and controls. Conclusions. Although the phenotype was transmitted to a second generation, we were unable to detect specific changes in DNA methylation, common histone modifications or small RNA profiles in sperm. We did however note increased variance in sperm methylation patterns following Dex exposure, which could be one mechanism underpinning the observed phenotype, alternatively, other germline epigenetic modifications or non-epigenetic mechanisms may be responsible for the transmission of programmed effects across generations in this model.