Male-transmitted transgenerational effects of the herbicide linuron on DNA methylation profiles in Xenopus tropicalis brain and testis.

ABSTRACT

The herbicide linuron can cause endocrine disrupting effects in Xenopus tropicalis frogs, including offspring that were never exposed to the contaminant. The mechanisms by which these effects are transmitted across generations need to be further investigated. Here, we examined transgenerational alterations of brain and testis DNA methylation profiles paternally inherited from grandfathers developmentally exposed to an environmentally relevant concentration of linuron. Reduced representation bisulfite sequencing (RRBS) revealed numerous differentially methylated regions (DMRs) in brain (3060 DMRs) and testis (2551 DMRs) of the adult male F2 generation. Key genes in the brain involved in somatotropic (igfbp4) and thyrotropic signaling (dio1 and tg) were differentially methylated and correlated with phenotypical alterations in body size, weight, hind limb length and plasma glucose levels, indicating that these methylation changes could be potential mediators of the transgenerational effects of linuron. Testis DMRs were found in genes essential for spermatogenesis, meiosis and germ cell development (piwil1, spo11 and tdrd9) and their methylation levels were correlated with the number of germ cells nests per seminiferous tubule, an endpoint of disrupted spermatogenesis. DMRs were also identified in several genes central for the machinery that regulates the epigenetic landscape including DNA methylation (dnmt3a and mbd2) and histone acetylation (hdac8, ep300, elp3, kat5 and kat14), which may at least partly drive the linuron-induced transgenerational effects. The results from this genome-wide DNA methylation profiling contribute to better understanding of potential transgenerational epigenetic inheritance mechanisms in amphibians.