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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]

To study the expression of four estrogen receptor genes ( erα1, erα2, erβ1, erβ2 ) of female rainbow trout ( Oncorhynchus mykiss ) during first ovarian development, trouts were sampled from different ovarian stages. Serum E 2 (estradiol) was measured by ELISA and estrogen receptors mRNA expression were examined by qRT-PCR. Our results showed a close association between increased erα1 and vitellogenin mRNA expression during ovarian maturation and increased erα2 mRNA expression in mature ovarian stages. Correlation analysis revealed that a negative relationship between serum E 2 and ovarian erβ1 (or hepatic erβ2 ), but ovarian erβ2 mRNA expression was relatively unchanged during first ovarian development. Trout were also reared in different densities as stocking density 1, 2 and 3 (SD1, 4.6–31.1 kg/m 3 ; SD2, 6.6–40.6 kg/m 3 ; SD3, 8.6–49.3 kg/m 3 ) to elucidate effects of high density on estrogen receptor expression. Histology observation showed ovarian development of trout in higher densities were retard with a relatively early stage and fewer vitellogenin accumulation. Trout in high densities showed significantly decreased serum E 2 , erα mRNA expression and increasing trends of erβ mRNA expression. A noticeable increase of ovarian erβ2 mRNA expression was seen in trout when density is approaching to 50 kg/m 3 . In conclusion, we may hypothesize that increased erβ mRNA expression triggered by high density result in decreased erα mRNA expression and vitellogenesis. As a result, ovarian development in higher densities was retard. [ABSTRACT FROM AUTHOR]