DNA methyltransferase expressions in Japanese rice fish (Oryzias latipes) embryogenesis is developmentally regulated and modulated by ethanol and 5-azacytidine

We aimed to investigate the impact of the epigenome in inducting fetal alcohol spectrum disorder (FASD) phenotypes in Japanese rice fish embryogenesis. One of the significant events in epigenome is DNA methylation which is catalyzed by DNA methyltransferase (DNMT) enzymes. We analyzed DNMT enzyme mRNA expressions in Japanese rice fish development starting from fertilized eggs to hatching and also in embryos exposed for first 48 h of development either to ethanol (300 mM) or to 5-azacytidine (5-azaC; 2 mM), an inhibitor of DNMT enzyme activity. As observed in FASD phenotypes, 5-azaC exposure was able to induce microcephaly and craniofacial cartilage deformities in Japanese rice fish. Moreover, we have observed that expression of DNMTs (dnmt1, dnmt3aa, and dnmt3bb.1) are developmentally regulated; high mRNA copies were found in early stages (1-2 day-post-fertilization, dpf), followed by gradual reduction until hatched. In ethanol-treated embryos, compared to controls, dnmt1 mRNA is in reduced level in 2 dpf and in enhanced level in 6 dpf embryos. While dnmt3aa and 3bb.1 remained unaltered. In contrast, embryos exposed to 5-azaC have an enhanced level of dnmt1 and dnmt3bb.1 mRNAs both in 2 and 6 dpf embryos while dnmt3aa is enhanced only in 6 dpf embryos. Moreover, endocannabinoid receptor 1a (cnr1a) mRNA which was found to be reduced by ethanol remained unaltered and cnr1b and cnr2 mRNAs, which were remained unaltered by ethanol, were increased significantly by 5-azaC in 6 dpf embryos. This study indicates that the craniofacial defects observed in FASD phenotypes are the results of dysregulations in DNMT expressions.