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In the livestock industry, meat color has become important because consumer acceptance is subject to the appearance of the product in the market-place. Our previous analyses of a whole genome QTL scan for various meat qualities using 2 F2 families from Japanese wild bar (known as a red meat) x Large White and from Duroc x Chinese Jinhua suggested that a meat color (heme content) QTL is located on SSC6. The objective, of this study was to fine-map this SSC6 meat color QTL and subsequently investigate positional candidate genes for polymorphisms that may cause changes in meat color. Therefore, we conducted interval mapping on SSC6 using an additional 9 gene markers through combined analyses of the 2 F2 families of Japanese wild boar x Large White (353 progeny) and Duroc x Chinese Jinhua (204 progeny). Comparative analysis with humans, mice, and cattle suggested that there were 10 functional genes in the region. Among these genes, we suggested that a novel pig gene encoding a nudix (nucleoside diphosphate linked moiety X)-type motif 7 (NUDT7, a member of the nudix hydrolases) is a strong candidate for the QTL because the mouse Nudt7 is reported to hydrolyze succinyl- CoA, a substrate of the reaction limiting the rate of heme biosynthesis. We therefore determined the pig NUDT7 gene sequence including the 5' promoter region and explored genetic polymorphisms between Japanese wild boar and Large White. We identified 116 polymorphisms within the NUDT7 CDS or in the 5' region. None of the AA substitutions were associated with the meat color QTL; however, 3 polymorphisms were found in putative transcription factor recognition sites. We then investigated the differential expression of NUDT7 in Japanese wild boar and Large White by'allele-specific quantitative real-time PCR. The expression level of the Large White type allele was greater than that of the Japanese wild-boar-type allele. Consequently, we speculated that the difference in meat color between Japanese wild boar and Large White is caused partly by differential expression of this candidate gene. Up- regulation of NUDT7 expression in muscle may reduce succinyl-CoA content and thus reduce the level of herne biosynthesis. [ABSTRACT FROM AUTHOR]

Three generations of a swine family produced by crossing a Japanese wild boar and three Large White female pigs were used to map QTL for various production traits. Here we report the results of QTL analyses for skeletal muscle fiber composition and meat quality traits based on phenotypic data of 353 F2 animals and genotypic data of 225 markers covering almost the entire pig genome for all of the F2 animals as well as their F1 parents and F0 grandparents. The results of a genome scan using least squares regression interval mapping provided evidence that QTL (<1% genome-wise error rate) affected the proportion of the number of type IIA muscle fibers on SSC2, the number of type IIB on SSC14, the relative area (RA) of type I on SSCX, the BA of type IIA on SSC6, the RA of type IIB on SSC6 and SSC 14, the Minolta a* values of loin On SSC4 and SSC6, the Minolta b* value of loin on SSC15, and the hematin content of the LM on SSC6. Quantitative trait loci (<5% genome-wise error rate) were found for the number of type I on SSC1, SSCI4, and SSCX, for the number of type IIA on SSCI4, for the number of type JIB on SSC2, for the RA of type hA on SSC2, for the Minolta b* value of loin on SSC3, for the pH of loin on SSC15, and for the i.m. fat content on SSC15. Twenty-four QTL were detected for 11 traits at the 5% genome-wise level. Some traits were associated with each other, so the 24 QTL were located on 11 genomic regions. In five QTL located on SSC2, SSCG, and SSC14, each wild boar allele had the effect of increasing types I and IJA muscle fibers and decreasing type IIB muscle fibers. These effects are expected to improve meat quality. [ABSTRACT FROM AUTHOR]