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Abstract: Cytochrome P450c17-II (cyp17-II) gene is an important factor affecting the growth, gonad differentiation and development, and other reproductive traits of fish. There are three CpG rich regions in the coding region of cyp17-II gene in Japanese flounder (Paralichthys olivaceus). The aim of this study was to understand whether mutations in exons of the cyp17-II gene occured at CpG sites, and mutations and methylation status of those CpG sites were involved in regulation of the expression level of cyp17-II gene and the reproductive endocrine of Japanese flounder. The results showed that three single nucleotide polymorphisms (SNPs) were identified. SNP1 [(c. G594A (p.Gly 188Arg)] located in exon 4 of L1 locus, and SNP2 (c.A939G) and SNP3 (c.C975T) of L2 locus located in CpG rich region of the exon 6 of cyp17-II gene. Furthermore, the A to G transition at 939bp position added a new methylation site to the cyp17-II coding region. According to multiple-comparison analysis, two loci (L1 and L2) were significantly associated with serum testosterone (T) level (P< 0.05) and the expression of cyp17-II in ovary (P< 0.01). Intriguingly, individuals with GG genotype of L2 locus containing eight CpG methylation sites had significantly lower serum testosterone level and cyp17-II mRNA expression than those with AA genotype containing seven CpG methylation sites. Moreover, the CpG site was highly methylated (⩾77.8%) at 938bp position of individuals with GG genotype of L2 locus. These implied that the mutation and methylation status of the coding region of cyp17-II could influence the gene expression and the reproductive endocrine levels in female Japanese flounder and L2 locus could be regarded as a candidate genetic or epigenetic marker for Japanese flounder breeding programs. [Copyright &y& Elsevier]

• The methylation and expression of myomaker was assessed in Paralichthys olivaceus. • Myomaker expression increased throughout postnatal development. • Methylation was negatively correlated with myomaker expression. • Myomaker is likely a key myoblast fusion and muscle formation gene in P. olivaceus. Myomaker is a membrane protein that plays a crucial role in the fusion of myoblasts during muscle growth. DNA methylation, a significant factor, regulates gene expression. The aim of this study was to examine the methylation and mRNA expression patterns of the myomaker gene during 8 different postnatal developmental stages in the Japanese flounder (L: 7 days post hatch (dph); M1: 21 dph; M2: 28 dph; M3: 35 dph; J1: 90 dph; J2: 180 dph; A1: 24 months; A2: 36 months). Muscle tissue samples were taken from Japanese flounder at different postnatal development stages to measure the extent of DNA methylation and gene expression. Methylation level in the promoter and exon 1 of myomaker was measured using bisulfite sequencing, and the relative expression of myomaker during each developmental stage was measured by quantitative PCR. The relative expression levels of myomaker were up-regulated from stages L to M2, M3 to J2, and methylation of myomaker was negatively correlated with mRNA expression. Furthermore, the CpG site located at −26 bp in the promoter was the lowest methylated region in all developmental stages. These results offer a basis for understanding the mechanism by which myomaker regulates muscle formation during postnatal development. [ABSTRACT FROM AUTHOR]