The molecular genetic basis of feeding, growth and lean efficiency traits in pigs
The advent of a detailed porcine genetic map has facilitated the search for loci harbouring polymorphisms with effects on economically important performance traits. The high level of sequence identity between the human and pig genome means pigs can also be a useful animal model species for human diseases, such as obesity. In this study, quantitative trait loci (QTL) and candidate genes related to energy balance and obesity was investigated in an F2 population derived from a cross between Meishan and Large White lines, and populations of divergently selected Large White lines. The main findings of the study were: 1. A significant QTL affecting daily feed intake on chromosome 2 was identified and found to co-localize with a known regulatory mutation with major effects on body composition traits. 2. A number of suggestive QTL were located, including QTL affecting meal size and growth traits in the region of chromosome 8 to which the cholecystokinin type-A receptor (CCKAR) maps. 3. A CCKAR gene polymorphism was found to be associated with performance traits in the F2 population and in divergently selected Large White lines. 4. A Melanocortin-4 receptor (MC4R) polymorphism showed an association with feed intake, growth and fatness in the divergent selection lines. 5. A novel polymorphism in the 5’ untranslated region (5’UTR) of the CCKAR gene was shown to disrupt the binding of the transcriptional regulator yin yang 1 (YY1). These results suggest that the previously identified major regulatory mutation on chromosome 2 may be associated with pleiotropic effects on feed intake, with implications for its potential uses in marker-assisted selection. Also, the results from the CCKAR association study show that CCKAR may have effects on performance traits, and a 5’UTR polymorphism which disrupts YY1 binding may be a causal variant. This highlights the value of utilizing research into human obesity to choose suitable candidate genes for performance in livestock.