Association of genetic variants and expression levels of porcine FABP 4 and FABP 5 genes

Summary The FABP 4 and FABP 5 genes, coding for fatty acid transport proteins, have long been studied as positional candidate genes for SSC 4 QTL affecting fat deposition and composition traits in pigs. Polymorphisms in these genes, FABP 4 :g.2634_2635insC and FABP 5 :g.3000T>G, have previously been associated with fatness traits in an Iberian by Landrace cross ( IBMAP ). The aim of the present work was to evaluate the functional implication of these genetic variants. For this purpose, FABP 4 and FABP 5 mRNA expression levels in 114 BC 1_ LD animals (25% Iberian × 75% Landrace) were analyzed using real‐time quantitative PCR in backfat and muscle. FABP 4 gene expression in backfat, but not in muscle, was associated with FABP 4 :g.2634_2635insC. In contrast, FABP 5 :g.3000T>G was not associated with gene expression levels. An expression‐based genome‐wide association study highlighted the FABP 4 :g.2634_2635insC polymorphism as the polymorphism most associated with FABP 4 gene expression in backfat. Furthermore, other genomic regions associated in trans with the mRNA expression of FABP 4 in backfat and FABP 5 in muscle were also identified. Finally, two putative transcription binding sites for PPARG and NR 4A2 may be affected by the FABP 4 :g.2634_2635insC polymorphism, modifying FABP 4 gene expression. Our results reinforce FABP 4 as a candidate gene for fatness traits on SSC4.