Permanent gonadal epigenetic changes in response to heat during early development in zebrafish.

Abstract

The environment can influence the epigenome through modifications that alter gene expression and, consequently, can produce the appearance of a new phenotype. DNA methylation and regulatory microRNAs (miRNAs) are two types of epigenetic mechanisms responsible to integrate environmental cues. In fish, epigenetic modifications can follow as result of external inputs, and some can affect sex determination and differentiation. However, the underlying molecular mechanisms remain poorly understood. Currently, the search for epigenetic biomarkers (epimarkers) to identify specific phenotypes is at the forefront of research. The present study aimed to find epimarkers (DNA methylation and miRNAs) in mature fish gonads linked to abnormal thermal conditions that these fish might have suffered during early gonadal development. Zebrafish (Danio rerio) larvae were exposed to either control or high temperature during sex differentiation (18¿32 days post fertilization). DNA methylation in the promoter region of a set of key genes related to sexual development was studied in adult gonads by a targeted sequencing approach (Multiplex Bisulfite Sequencing, MBS). miRNA expression was explored with RNA-seq using Illumina technology. Furthermore, the spatial distribution of a selection of miRNAs was studied in the ovaries and testes by fluorescent in situ hybridization (FISH). Results showed differences in the methylation level of the promoter of some genes between sexes and temperatures, thus allowing to predict, by machine-learning strategies, epimarkers associated with sex and previous thermal exposure. By biocomputational analysis, we identified 24 unique miRNAs targeting 402 RNA transcripts and that responded differentially to heat in the gonads. Some of these miRNAs were mostly located to germ cells. This study identified DNA methylation and miRNAs changes in the zebrafish adult gonads that can be considered permanent epimarkers of past thermal events. This work was supported by MINECO grants AGL2016-787107-R "Epimark" to FP, AGL2015-73864-JIN "Ambisex" to LR and scholarship BES-2014¿069051 to AV. This study identified DNA methylation and miRNAs changes in the zebrafish adult gonads that can be considered permanent epimarkers of past thermal events. This study identified DNA methylation and miRNAs changes in the zebrafish adult gonads that can be considered permanent epimarkers of past thermal events. Currently, the search for epigenetic biomarkers (epimarkers) to identify specific phenotypes at the forefront of research