Thirteen candidate genes for human obesity were selected for cytogenetic mapping by FISH in the pig genome. Among them, 6 genes were assigned to chromosomes for the first time (NR3C1, GNB3, ADRB1, ADRB2, ADRB3 and UCP1). Location of the other 7 genes (INSIG2, LIPIN1, PLIN, NAMPT, ADIPOQ, UCP2 and UCP3), earlier mapped by somatic cell hybridization or with the use of a radiation hybrid panel, was verified (INSIG2) or more precisely described. The genes were assigned to the following chromosomes: INSIG2 to SSC15q12, LIPIN1 to SSC3q26, NR3C1 to SSC2q29, PLIN to SSC7q15, GNB3 to SSC5q21, NAMPT to SSC9q23, ADIPOQ to SSC13q41, ADRB1 to SSC14q28, ADRB2 to SSC2q29, ADRB3 to SSC15q13-14, UCP1 to SSC8q21-22, and both UCP2 and UCP3 to SSC9p24. Most of the genes were located within known QTL for pig fatness traits.
Fat accumulation is a polygenic trait which has a significant impact on human health and animal production. Obesity is also an increasingly serious problem in dog breeding. The FTO and INSIG2 are considered as candidate genes associated with predisposition for human obesity. In this report we present a comparative genomic analysis of these 2 genes in 4 species belonging to the family Canidae – the dog and 3 species which are kept in captivity for fur production, i.e. red fox, arctic fox and Chinese raccoon dog. We cytogenetically mapped these 2 loci by FISH and compared the entire coding sequence of INSIG2 and a fragment of the coding sequence of FTO. The FTO gene was assigned to the following chromosomes: CFA2q25 (dog), VVU2q21 (red fox), ALA8q25 (arctic fox) and NPP10q24–25 (Chinese raccoon dog), while the INSIG2 was mapped to CFA19q17, VVU5p14, ALA24q15 and NPP9q22, respectively. Altogether, 29 SNPs were identified (16 in INSIG2 and 13 in FTO) and among them 2 were missense substitutions in the dog (23C/T, Thr>Met in the FTO gene and 40C/A, Arg>Ser in INSIG2). The distribution of these 2 SNPs was studied in 14 dog breeds. Two synonymous SNPs, one in the FTO gene (–28T>C in the 5′-flanking region) and one in the INSIG2 (10175C>T in intron 2), were used for the association studies in red foxes (n = 390) and suggestive evidence was observed for their association with body weight (FTO, p < 0.08) and weight of raw skin (INSIG2, p < 0.05). These associations indicate that both genes are potential candidates for growth or adipose tissue accumulation in canids. We also suggest that the 2 missense substitutions found in dogs should be studied in terms of genetic predisposition to obesity.
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