DNA methylation levels and expression patterns of Smyd1a and Smyd1b genes during Metamorphosis of the Japanese Flounder (Paralichthys olivaceus).

Japanese flounder (Paralichthys olivaceus) undergoes metamorphosis by changing its body from the larval to the juvenile form, and this process involves muscle development. Smyd1, a histone methyltransferase, plays a role in the skeletal muscle. In the present study, the Smyd1a and Smyd1b expression patterns and their 5' UTR and exon 1 DNA methylation levels were analyzed during metamorphosis of the Japanese flounder. Sample were analyzed 21 days post-hatching (dph) (with no migration of right eye; M1stage), 28 dph (during migration of right eye; M2 stage), and 35 dph (after migration of right eye; M3 stage). The results show that Smyd1a expression was highest in the M2 stage and then decreased, whereas Smyd1b expression continued to rise during the three stages. Methylation levels of CpG sites at positions -2318 and -2217 of the Smyd1a P region (-2462 to -2181 region of the 5' UTR), and the CpG sites at positions -351, -330, -284, -190, and - 92 of the Smyd1b promoter, with both regions containing putative transcription factor binding sites, showed significant differences in the three stages (p < 0.05). Interestingly, the methylation levels of these CpG sites were negatively correlated with mRNA expression. We inferred that binding of the predicted transcription factors might be affected by methylation of the CpG sites and thus modulate gene expression. Taken together, our results suggest that DNA methylation in the Smyd1a and Smyd1b genes participates in the regulation of metamorphosis, and epigenetics may provide clues for further studies of the mechanisms of metamorphosis in the Japanese flounder.