New investigations around CYP11A1 and its possible involvement in an androstenone QTL characterised in Large White pigs

Abstract

Background: Previously, in boars with extreme androstenone levels, differential expression of the CYP11A1 gene in the testes has been characterised. CYP11A1 is located in a region where a QTL influencing boar fat androstenone levels has been detected in a Large White pig population. Clarifying the role of CYP11A1 in boar taint is important because it catalyses the initial step of androstenone synthesis and also of steroid synthesis.

Results: A genome-wide association study located CYP11A1 at approximately 1300 kb upstream from SNP H3GA0021967, defining the centre of the region containing the QTL for androstenone variation. In this study, we partially sequenced the CYP11A1 gene and identified several new single nucleotide polymorphisms (SNP) within it. Characterisation of one animal, heterozygous for CYP11A1 testicular expression but homozygous for a haplotype of a large region containing CYP11A1, revealed that variation of CYP11A1 expression is probably regulated by a mutation located downstream from the SNP H3GA0021967. We analysed CYP11A1 expression in LW families according to haplotypes of the QTL region's centre. Effects of haplotypes on CYP11A1 expression and on androstenone accumulation were not concordant.

Conclusion: This study shows that testicular expression of CYP11A1 is not solely responsible for the QTL influencing boar fat androstenone levels. As a conclusion, we propose to refute the hypothesis that a single mutation located near the centre of the QTL region could control androstenone accumulation in fat by regulating the CYP11A1 expression.

Figure 1

Schematic representation of the SSC7 and human homologous regions. Center part: schematic representation of genes in the 64-69 Mb SSC7 region (in accordance with the sscrofa9 draft sequence); top left hand side: HSA15 segment homologous to the left half of this SSC7 region; lower right hand side: HSA14 segment homologous to the right half of this SSC7region; each gene sequence is represented by an arrow i.e. full arrow if homologous porcine gene exists and hollow arrow if not; lower left hand side: representation of part of the porcine sequence gap including CYP11A1 with its structure schematized showing the location of the polymorphisms characterised in this study i.e. one SNP (R in IUPAC codification) and one microsatellite identified in the distant 5' flanking sequence; SNP (Y) patented by Greger [18] was found in the proximal promoter and SNP (R) previously characterised by Grindfleck et al. [12] was found in the first exon; two new SNP (R and R) in the first intron and two consecutive SNP (WK) in the second intron were also detected; composition and position in Mb (Sscrofa9) of SNP marker groups: (1) over the 64.38-64.65 Mb region with M1 = ALGA0042289; M2 = INRA0026201; M3 = ASGA0034277; M4 = DRGA007689; M5 = ALGA0042294; M6 = H3GA0021937; (2) over the 65.13-65.33 Mb region with M7 = ASGA0034288; M8 = INRA0026223; M9 = ALGA0042315; M10 = ASGA0034291; (3) over the 65.91-66.11 Mb region with M11 = H3GA0021967; M12 = ASGA0034309; M13 = ASGA0034310; M14 = MARC0076146 and (4) over the 68.27-68.56 Mb region with M15 = INRA0026286; M16 = MARC0099388; M17 = inra0026290; M18 = ALGA0042359