Analysis of the genetic basis of porcine meat quality and coat color by using genomic and transcriptomic tools
The main objectives of this Thesis were to investigate the genetic basis of fatness in pigs and to identify the genetic factors involved in the establishment of blond vs red pigmentation patterns in Mangalitza pigs by using genomic and transcriptomic tools. In the first study of the Thesis (Chapter 3) we compare the skeletal muscle expression patterns of two groups of Duroc pigs with different growth and fatness profiles (HIGH: high backfat thickness, intramuscular fat, saturated and unsaturated fatty acid content and serum lipids vs LOW: opposite phenotypes) By using a RNA Seq technology, we identified 96 genes differentially expressed. Several of these genes are related to lipid metabolism (e.g. SLC27A4, SFRP5 and CES1) and the transcription factor PPARG appears to be a key regulator of porcine fatness. We have also observed that very few non coding RNAs are differentially expressed in these two groups of pigs, suggesting that the non coding transcriptome has a limited effect on the establishment of the HIGH and LOW phenotypes. In the second study of the Thesis, we demonstrate the differential expression of specific mRNA isoforms of four genes with a known role in obesity (ITGA5, LITAF, TIMP1 and ANXA2) in HIGH vs LOW pigs. The differential expression of these isoforms may have effects on transcript structure as well as on the protein sequence. In the third study, we aimed to investigate the differential expression of mRNA encoding genes in response to food ingestion. This goal has been achieved by comparing the muscle mRNA expression patterns of Duroc sows before feeding (T0) and 5 h. (T1) and 7 h. (T2) after feeding. Besides genes with a well known role in energy homeostasis (e.g. PFKFB3 and G0S2) we have identified several genes with a plausible but poorly characterized role in metabolism (e.g. MIGA2, SDC4, and CSRNP1) We have also observed that the set of genes differentially expressed before and after feeding is enriched in transcription factors and pathways related to oxidative stress, angiogenesis, and circadian rhythms. Considering these results, in the fourth study we use quantitative RT qPCR technique to find out how the expression of 8 circadian genes (ARNTL, BHLHE40, CRY2, NPAS2, NR1D1, PER1, PER2 and SIK1) changes in response to food ingestion in five porcine tissues i.e. skeletal muscle, hypothalamus, liver, intestine and dorsal fat. Our results indicate that the expression of the Clock genes does not change in the hypothalamus, the tissue containing the central clock entrained by light, but in contrast, it is strongly modified in the other four tissues. This finding demonstrates that nutrition changes the expression of circadian genes integrated in peripheral clocks. Finally, in the fifth study, we have analysed, in collaboration with researchers of the Research Institute for Animal Breeding and Nutrition (Hungary) and the University of Cluj Napoca (Romania) the genetic basis of coat color (red vs blond) of Mangalitza pigs. By combining a selection scan and a genome wide association study, we have found that the SLC45A2 gene is probably involved in the genetic determination of pigmentation in Mangalitza pigs, a result that agrees well with previous studies demonstrating the implication of this locus on the color patterns of multiple mammalian species including humans. More specifically, two missense SNPs c.806G>A (p.Gly269Glu) and c.956G>A (p.Arg319His) in the SLC45A2 locus appear to be strongly but not fully associated with the red and blond coat colors of Mangalitza pigs. This finding suggests the existence of additional genetic factors regulating the pigmentation of Mangalitza pigs.