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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]

• Screening candidate circpdlim5a from the Japanese flounder transcriptome. • Circpdlim5a has a stable structure and high RNase R tolerance. • Distributed in nucleus and cytoplasm and highly expressed in nucleus. • Circpdlim5a inhibits the expression of proliferation and differentiation genes. Circular RNAs (circRNAs) are non-coding RNAs with endogenous regulatory functions, including regulating skeletal muscle development. However, its role in the development of skeletal muscle in Japanese flounder (Paralichthys olivaceus) is not clear. Therefore we screened a candidate circpdlim5a, which is derived from the gene pdlim5a , from the skeletal muscle transcriptome of Japanese flounder. We characterized circpdlim5a, which was more stable compared to the linear RNA pdlim5a. Distributional characterization of circpdlim5a showed that circpdlim5a was predominantly distributed in the nucleus and was highly expressed in the skeletal muscle of adult Japanese flounder (24 months). When we further studied the circpdlim5a function, we found that it inhibited the expression of proliferation and differentiation genes according to the over-expression experiment of circpdlim5a in myoblasts. We concluded that circpdlim5a may inhibit the proliferation and differentiation of myoblasts and thereby inhibit skeletal muscle development in Japanese flounder. This experiment provides information for the study of circRNAs by identifying circpdlim5a and exploring its function, and offers clues for molecular breeding from an epigenetic perspective. [ABSTRACT FROM AUTHOR]

• 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]