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Metabolic and histochemical characteristics of fat and muscle tissues in homozygous or heterozygous pigs for the body composition QTL located on chromosome 7

¹ Institut National de la Recherche Agronomique (INRA), Unité Mixte de Recherche (UMR)444, Laboratoire de Génétique Cellulaire, BP52627, Castanet-Tolosan
² INRA, Unité de Recherche (UR)337, Station de Génétique Quantitative et Appliquée, Jouy en Josas
³ INRA, Unité d'Enseignement (UE)967, Domaine expérimental du Magneraud, Surgères
⁴ INRA, UR1213, Unité de Recherches sur les Herbivores, Saint Genès Champanelle
⁵ INRA, UMR1079, Systèmes d'Elevage Nutrition Animale et Humaine, Saint-Gilles, France

Quantitative trait loci (QTL) influencing many traits including backfat thickness and carcass composition have been detected on porcine chromosome 7 (SSC7) in an F2 cross between Large White (LW) and Meishan (MS) pigs. However, the genes and controlled pathways underlying the QTL effects on body phenotype remain unknown. This study aimed at investigating the tissue characteristics at metabolic and cellular levels in pigs that were either homozygous or heterozygous for a body composition SSC7 QTL. A backcross pig (BC3) was first progeny tested to confirm its heterozygoty for the SSC7 QTL; results on all offspring (n = 80) confirmed the QTL effects on body fatness. This boar was then mated with three sows known to be heterozygous for this QTL. In the subset of pigs per genotype, we found that heterozygous LW_QTL7/MS_QTL7 pigs had smaller adipocytes in backfat, together with a lower basal rate of glucose incorporation into lipids and lower activities of selected lipogenic enzymes in backfat isolated cells, compared with homozygous LW_QTL7/LW_QTL7 pigs. A higher number of adipocytes was also estimated in backfat of LW_QTL7/MS_QTL7 animals compared with LW_QTL7/LW_QTL7 pigs. The SSC7 QTL did not influence oxidative and glycolytic metabolisms of longissimus and trapezius muscles, as estimated by the activities of specific energy metabolism enzymes, or the myofiber type properties. Altogether, this study provides new evidence for an altered adipocyte cellularity in backfat of pigs carrying at least one MS allele for the SSC7 QTL. Some candidate genes known for their functions on adipocyte growth and differentiation are suggested.

quantitative trait locus; porcine chromosome 7; energy metabolism; lipogenesis; adipocytes