Abstract
BackgroundThis descriptive study of the abdominal fat transcriptome takes advantage of two experimental lines of meat-type chickens (Gallus domesticus), which were selected over seven generations for a large difference in abdominal (visceral) fatness. At the age of selection (9 wk), the fat line (FL) and lean line (LL) chickens exhibit a 2.5-fold difference in abdominal fat weight, while their feed intake and body weight are similar. These unique avian models were originally created to unravel genetic and endocrine regulation of adiposity and lipogenesis in meat-type chickens. The Del-Mar 14K Chicken Integrated Systems microarray was used for a time-course analysis of gene expression in abdominal fat of FL and LL chickens during juvenile development (1–11 weeks of age).ResultsMicroarray analysis of abdominal fat in FL and LL chickens revealed 131 differentially expressed (DE) genes (FDR≤0.05) as the main effect of genotype, 254 DE genes as an interaction of age and genotype and 3,195 DE genes (FDR≤0.01) as the main effect of age. The most notable discoveries in the abdominal fat transcriptome were higher expression of many genes involved in blood coagulation in the LL and up-regulation of numerous adipogenic and lipogenic genes in FL chickens. Many of these DE genes belong to pathways controlling the synthesis, metabolism and transport of lipids or endocrine signaling pathways activated by adipokines, retinoid and thyroid hormones.ConclusionsThe present study provides a dynamic view of differential gene transcription in abdominal fat of chickens genetically selected for fatness (FL) or leanness (LL). Remarkably, the LL chickens over-express a large number of hemostatic genes that could be involved in proteolytic processing of adipokines and endocrine factors, which contribute to their higher lipolysis and export of stored lipids. Some of these changes are already present at 1 week of age before the divergence in fatness. In contrast, the FL chickens have enhanced expression of numerous lipogenic genes mainly after onset of divergence, presumably directed by multiple transcription factors. This transcriptional analysis shows that abdominal fat of the chicken serves a dual function as both an endocrine organ and an active metabolic tissue, which could play a more significant role in lipogenesis than previously thought.
Highlights
This descriptive study of the abdominal fat transcriptome takes advantage of two experimental lines of meat-type chickens (Gallus domesticus), which were selected over seven generations for a large difference in abdominal fatness
Using K-means clustering, we found that the expression profiles for most genes involved in coagulation were clustered with those of adipokines; this general trend was verified by quantitative reverse transcription PCR (qRT-PCR) analysis (Figures 3 and 4)
The up-regulation of thioredoxin interacting protein (TXNIP) in abdominal fat of the fat line (FL) during the period of maximal fatness (3–11 wk) could contribute to their enhanced lipogenesis and adiposity. We have discovered another putative sensor of glucose, the sweet taste receptor 1 (TAS1R1) gene, which is differentially expressed in the hypothalamus [79] and abdominal fat (Figure 2) of FL and lean line (LL) chickens
Summary
This descriptive study of the abdominal fat transcriptome takes advantage of two experimental lines of meat-type chickens (Gallus domesticus), which were selected over seven generations for a large difference in abdominal (visceral) fatness. At the age of selection (9 wk), the fat line (FL) and lean line (LL) chickens exhibit a 2.5-fold difference in abdominal fat weight, while their feed intake and body weight are similar These unique avian models were originally created to unravel genetic and endocrine regulation of adiposity and lipogenesis in meat-type chickens. Chickens normally exhibit “hyperglycemia” [7,8], insulin resistance [8,9,10,11], hepatic de novo synthesis of lipids [12] and, like humans [13], abdominal (visceral) fatness is a polygenic trait [14,15,16,17,18,19] Despite their relative insensitivity to insulin, acute immunoneutralization of insulin in the chicken provokes differential expression of more than a thousand genes in both liver and in skeletal muscle [20]. These observations support the chicken as a unique model for the study of the genetic and biological mechanisms controlling fatness or leanness
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