Current pigs are very efficient biological machines converting feed into meat, but the problem with their meat is precisely that it suffers from a lack of intramuscular fat; present pigs yield meat of low sensorial quality because many meat quality traits such as taste, juiciness or flavor are strongly dependent on intramuscular fat content.
Finding SNPs that could simultaneously increase intramuscular fat, to improve meat quality, and reduce backfat thickness (BT), to improve the economy of pig production, is not easy due to the already mentioned positive genetic correlation between both traits, but it is not impossible. In the search for more SNPs able to simultaneously reduce BT and to increase IMF content we have directed our attention to comparative biology: in 2007 a transgenic mouse overexpressing 100 fold the cytosolic form of phosphoenolpyruvate carboxykinase (Pck1) in skeletal muscle was shown to have almost four fold larger intramuscular fat content (IMF) and strongly reduced amounts of both subcutaneous and visceral fat. Because this is exactly the desirable phenotype in pig breeding schemes we thought that the Pck1 pig gene could be a good candidate to search for variability.
To study the potential role of Pck1 in fat deposition and distribution in the pig we have sequenced the whole promoter and coding regions of the Pck1 gene in breeds or crosses (Iberian, Piètrain, Duroc x Landrace/Large White) that differ amply in fat-related traits. In this analysis we have found a SNP in the coding sequence of Pck1 that results in a methionine to leucine substitution. This SNP is strongly associated to changes in fat content and distribution and also on meat quality in the Duroc x Landrace/Large White cross; the analysis of the effects of the SNP on kinetic, structural and functional properties of purified Pck1 also reveals significant differences between Pck1 isoenzymes, reinforcing the hypothesis that c.A2456C contributes to the phenotypic changes detected in the Duroc x Landrace/Large White cross. We analyzed the c.A2456C substitution in the Pck1 gene in 202 animals from the same Du x LD/LW cross to evaluate its effects on fat distribution and meat quality traits. The genotypic frequencies in this cross were 0.361 AA, 0.565 AC and 0.074 CC.
The A allele is clearly associated to larger (up to 20.4%) IMF content in two of the three analyzed muscles and also to 9.9% lower BT, showing also a similar, although not as extreme, pattern to the transgenic Pck1 mouse. In addition, a strong association was found between higher water holding capacity at several time points postmortem and the A allele. This elevated (up to 24%) water holding capacity is probably related to the higher values of pH24 also associated to A alleles.
Pedro Latorre, Carmen Burgos, Jorge Hidalgo, Luis Varona, José Alberto Carrodeguas and Pascual López-Buesa. c.A2456C-substitution in Pck1 changes the enzyme kinetic and functional properties modifying fat distribution in pigs. Scientific Reports 6, Article number: 19617 (2016). doi:10.1038/srep19617