Fine Mapping Of QTL And Identification Of Positional Candidate Genes For Boar Reproduction Triats On SSC7

Boar reproduction traits are economically important traits in the pig industry.However, these traits are difficult to improve by conventional breeding due to its lowheritability. Deciphering the genetic basis of boar reproductivity will not only affordingnovel molecular breeding technology for boar selection, but also provide referencedinformation for man infertility study.In the present study,205F2boars from a White Duroc×Erhualian resourcepopulation were used for genetic dissection of boar reproduction traits such as epididymalweight, serum testosterone concentration and semen quality.14SNPs in the preliminaryQTL region for epididymal weight were used as markers to scan205F2boars and theirparents by real-time Taqman PCR or direct sequencing. Fine mapping analyses revealedthat the QTL region for epididymal weight was narrowed from24.5cM (48.5-73cM) to15cM (57-72cM), and another QTL for serum testosterone concentration was narrowed from70.5cM (4.5-75cM) to33cM (40-73). The F values for these two QTL were increasedfrom23.76and10.68to45.24and14.87, respectively.60K SNP data obtained bygenotype imputation for these205F2boars was used for GWAS analysis, and28SNPsthat significantly associated with epididymal weight, sperm concentration and total spermper ejaculate were detected (P <0.01).MEA1and TEP1, two genes in the regions of QTL fine mapping and GWAS analysiswere chosen as positional candidate genes for boar reproduction traits. Totally50SNPswere found in these two genes, of which24SNPs (10from promoters and exons) weregenotyped by direct sequencing. Variance analysis showed that5SNPs of MEA1werehighly significantly associated with boar epididymal weight, serum testosteroneconcentration and semen quality (P <0.01).11SNPs of TEP1were extremely significantlyassociated with epididymal weight (P <0.01) and7were highly significantly associatedwith semen quality (P <0.01). Association of MEA1g.-809T>C with epididymal weightshowed the most significant P value (P=8.59E-16). F-drop test was applied to determinethe effects of SNPs on boar reproduction. The results showed that the QTL effects forepididymal weight decreased at different degrees whereas still reach significant levels.However, F-drop analyses of MEA1g.-1168A>G and MEA1g.1115A>G indicating thedisappearance of QTL effects for serum testosterone concentration. It means that these twoSNPs should be complete linkage disequilibrium with the QTG or QTN for boar serumtestosterone concentration.qRT-PCR analyses revealed significant differences between genotypes of MEA1g.-809T>C and TEP1g.9949G>A and expression level of these two genes in epididymistissue. G genotype of TEP1g.9949G>A has the effect of increasing epididymal weight.QTT analyses showed that epididymal weight has negative association with MEA1and TEP1expression level in this tissue (r are-0.300and-0.525, respectively). qRT-PCRanalyses detected the expression of MEA1and TEP1genes in all18selected tissues of amature boar.This study establishes a foundation for developing molecular markers and furtheridentification of causative genes for boar reproduction traits.