Early-life stress changes expression of GnRH and kisspeptin genes and DNA methylation of GnRH3 promoter in the adult zebrafish brain

• Early-life DEX treatment increased expressions of GnRH2–3 and Kiss1–2 mRNA.
• DEX exposure in early-life affected adult testes development and spermatogenesis.
• Early-life DEX increased methylation at −1410, −1377 and −1355 CpG on GnRH3 promoter.
• Early-life stress has long-term impact on reproduction and DNA methylation in the brain.

Early-life stress can cause long-term effects in the adulthood such as alterations in behaviour, brain functions and reproduction. DNA methylation is a mechanism of epigenetic change caused by early-life stress. Dexamethasone (DEX) was administered to zebrafish larvae to study its effect on reproductive dysfunction. The level of GnRH2, GnRH3, Kiss1 and Kiss2 mRNAs were measured between different doses of DEX treatment groups in adult zebrafish. Kiss1 and GnRH2 expression were increased in the 200 mg/L DEX treated while Kiss2 and GnRH3 mRNA levels were up-regulated in the 2 mg/L DEX-treated zebrafish. The up-regulation may be related to programming effect of DEX in the zebrafish larvae, causing overcompensation mechanism to increase the mRNA levels. Furthermore, DEX treatment caused negative impact on the development and maturation of the testes, in particular spermatogenesis. Therefore, immature gonadal development may cause positive feedback by increasing GnRH and Kiss. This indicates that DEX can alter the regulation of GnRH2, GnRH3, Kiss1 and Kiss2 in adult zebrafish, which affects maturation of gonads. Computer analysis of 1.5 kb region upstream of the 5′ UTR of Kiss1, Kiss2, GnRH2 and GnRH3 promoter showed that there are putative binding sites of glucocorticoid response element and transcription factors involved in stress response. GnRH3 promoter analysed from pre-optic area, ventral telencephalon and ventral olfactory bulb showed higher methylation at CpG residues located on −1410, −1377 and −1355 between control and 2 mg/L DEX-treated groups. Hence, early-life DEX treatment can alter methylation of GnRH3 gene promoter, which subsequently affects gene regulation and reproductive functions.