The obesity gene, FTO, is of ancient origin, up-regulated during food deprivation and expressed in neurons of feeding-related nuclei of the brain

The porcine fat mass and obesity associated (FTO) gene is associated with fat deposition in Italian Duroc pigs

In humans, common variants in the fat mass and obesity associated (FTO) gene are associated with body mass index and obesity. Here we sequenced exon 4, parts of introns 3 and 4 and two portions of the 3'-untranslated region of the porcine FTO gene in a panel of nine pigs of different breeds and identified three SNPs. Allele frequencies of the g.276T>G (AM931150) mutation were studied in seven pig breeds. This mutation was used to linkage-map FTO to SSC6. Association analyses between the g.276T>G polymorphism and several traits [pH of semimembranosus muscle and estimated breeding values (EBV) for average daily gain, back fat thickness, lean cuts, ham weight and feed:gain ratio] were carried out in 257 sib-tested Italian Large White pigs. Only feed:gain ratio showed P<0.05. A selective genotyping approach was applied, analysing two extreme and divergent groups of Italian Large White pigs selected on the basis of back fat thickness EBV (50 with most positive and 50 with most negative values). Fisher's exact test (two-tailed) was not significant when comparing the allele frequencies of these two groups. The same approach was used in the Italian Duroc breed for which two extreme and divergent groups of animals were selected according to visible intermuscular fat EBV. Differences of allele frequencies between these two groups were highly significant (P<0.00001, P<0.001 and P<0.0001, considering all animals or only two- or three-generation unrelated animals respectively), indicating association between the analysed FTO marker and intermuscular fat deposition.

The relative impact of chronic food restriction and acute food deprivation on plasma hormone levels and hypothalamic neuropeptide expression

Our understanding of the central regulation of food intake and body weight has increased tremendously through implication of a high number of neuropeptides. However, lack of all-embracing studies have made comparison difficult in the past. The objective of this study was to demonstrate the relative importance of the different neuropeptides in terms of involvement in appetite regulatory mechanisms. We quantified expression levels of 21 hypothalamic neuropeptides and circulating levels of leptin, insulin, corticosterone, adrenocorticotropic hormone, ghrelin and adiponectin in rats after acute food deprivation and chronic food restriction using validated quantitative real-time PCR and hormone measurements. Body weight, insulin and leptin were reduced whereas corticosterone was increased by both acute food deprivation and chronic food restriction. Our results confirmed the relative importance in body weight homeostasis of neuropeptide Y and proopiomelanocortin, which were increased and decreased as predicted. The expression of other neuropeptides previously attributed central roles in body weight homeostasis, e.g. melanin-concentrating hormone and orexin, appeared to be less affected by the treatments. Moreover, the expression of dynorphin, galanin-like peptide and neuropeptide B was dramatically reduced after both treatments. This suggests that the latter neuropeptides--although previously known to be involved in body weight homeostasis--may be of unexpected importance in states of negative energy balance.

New insights into the genetics of body weight

PURPOSE OF REVIEW

These last months, the wave of genome-wide association scans finally reached the shores of body weight and obesity complex trait. In parallel, thanks to the increasing sequencing and genotyping capacities, large studies on rare mutations can now be carried out.

RECENT FINDINGS

In this review, I tried to cover the most recent findings in genome-wide association analyses, the outcome of conclusions subsequently not replicated, and the weight of rare mutations with strong effects on common obesity. The strongest predictor of obesity, FTO, is responsible for 1% of the total heritability, and results from other genome-wide scans do not provide, so far, any clue of other variants of this effect size. Thus, monogenic obesity studies might well reinstall the importance of rare nonsynonymous mutations of already known genes, especially melanocortin-4 receptor gene, in the general population. Nevertheless, additional genome-wide association analyses and replication are expected to confirm these first intuitions.

SUMMARY

Initial results both support the common variant-common disease hypothesis because at least one such variant exists in FTO, and also tone down its importance because such variants may be fewer than expected. Moreover, having a polymorphism associated with body weight is clearly not the end but rather the beginning of a long search for the gene function and pathway.