title: From SNP co-association to RNA co-expression: novel insights into gene networks for intramuscular fatty acid composition in porcine.
abstract: BACKGROUND
  Fatty acids (FA) play a critical role in energy homeostasis and metabolic diseases; in the context of livestock species, their profile also impacts on meat quality for healthy human consumption. Molecular pathways controlling lipid metabolism are highly interconnected and are not fully understood. Elucidating these molecular processes will aid technological development towards improvement of pork meat quality and increased knowledge of FA metabolism, underpinning metabolic diseases in humans.
  
  
  RESULTS
  The results from genome-wide association studies (GWAS) across 15 phenotypes were subjected to an Association Weight Matrix (AWM) approach to predict a network of 1,096 genes related to intramuscular FA composition in pigs. To identify the key regulators of FA metabolism, we focused on the minimal set of transcription factors (TF) that the explored the majority of the network topology. Pathway and network analyses pointed towards a trio of TF as key regulators of FA metabolism: NCOA2, FHL2 and EP300. Promoter sequence analyses confirmed that these TF have binding sites for some well-know regulators of lipid and carbohydrate metabolism. For the first time in a non-model species, some of the co-associations observed at the genetic level were validated through co-expression at the transcriptomic level based on real-time PCR of 40 genes in adipose tissue, and a further 55 genes in liver. In particular, liver expression of NCOA2 and EP300 differed between pig breeds (Iberian and Landrace) extreme in terms of fat deposition. Highly clustered co-expression networks in both liver and adipose tissues were observed. EP300 and NCOA2 showed centrality parameters above average in the both networks. Over all genes, co-expression analyses confirmed 28.9% of the AWM predicted gene-gene interactions in liver and 33.0% in adipose tissue. The magnitude of this validation varied across genes, with up to 60.8% of the connections of NCOA2 in adipose tissue being validated via co-expression.
  
  
  CONCLUSIONS
  Our results recapitulate the known transcriptional regulation of FA metabolism, predict gene interactions that can be experimentally validated, and suggest that genetic variants mapped to EP300, FHL2, and NCOA2 modulate lipid metabolism and control energy homeostasis in pigs.
authors.affiliation: Centre de Recerca en Agrigenòmica (CRAG), Consorci CSIC-IRTA-UAB-UB, Campus UAB, Bellaterra 08193, Spain. yuliaxis@gmail.com.
authors.forename: Yuliaxis
authors.initials: Y
authors.lastname: Ramayo-Caldas
authors.forename: Maria
authors.initials: M
authors.lastname: Ballester
authors.forename: Marina R S
authors.initials: MR
authors.lastname: Fortes
authors.forename: Anna
authors.initials: A
authors.lastname: Esteve-Codina
authors.forename: Anna
authors.initials: A
authors.lastname: Castelló
authors.forename: Jose L
authors.initials: JL
authors.lastname: Noguera
authors.forename: Ana I
authors.initials: AI
authors.lastname: Fernández
authors.forename: Miguel
authors.initials: M
authors.lastname: Pérez-Enciso
authors.forename: Antonio
authors.initials: A
authors.lastname: Reverter
authors.forename: Josep M
authors.initials: JM
authors.lastname: Folch
mesh_terms: D000273:Adipose Tissue / Q000378:metabolism; D000818:Animals; D050881:E1A-Associated p300 Protein / Q000235:genetics / Q000378:metabolism; D005227:Fatty Acids / Q000737:chemistry* / Q000378:metabolism; D053263:Gene Regulatory Networks / Q000235:genetics*; D055106:Genome-Wide Association Study; D005838:Genotype; D008099:Liver / Q000378:metabolism; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*; D051958:Nuclear Receptor Coactivator 2 / Q000235:genetics / Q000378:metabolism; D010641:Phenotype; D020641:Polymorphism, Single Nucleotide; D011401:Promoter Regions, Genetic; D012313:RNA / Q000378:metabolism*; D013552:Swine; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D005227:Fatty Acids; D051958:Nuclear Receptor Coactivator 2; D014157:Transcription Factors; D012313:RNA; D050881:E1A-Associated p300 Protein