While an understanding of lipid metabolism in chickens is critical for a further improvement of food production, there are few studies concerning differences in lipid metabolism mechanisms between chickens and other species at a molecular level. Chickens have three PPAR gene subtypes (α, β, and γ) that function differently from those present in humans and mice. The chicken PPAR-gamma (cPPARγ) gene is shorter than that in humans and lacks a γ2 isoform. Moreover, in serum-free media, cPPARγ shows high transcriptional activity without exogenous ligands. Luciferase reporter assays were used to examine the effect of sera on cPPAR transcriptional activities and showed that adult bovine serum and chicken serum highly activate cPPARα and β functions. Moreover, we found that bezafibrate induces the transactivation function of cPPARβ, but not human PPARδ (human PPARβ ortholog). This ligand selectivity relies on one amino acid residue (chicken: Val419, human: Met444). These results show the possibilities for unique functions of cPPARs on chicken-specific lipid glucose metabolism. As such, a better understanding of the molecular mechanisms of lipid metabolism in chickens could result in higher productivity for the poultry industry. 1. Genomic Organization of Chicken PPARS (cPPARs) The mechanisms of lipid and glucose metabolism for energy storage and homeostasis differ between species in ways that are not fully understood. To improve food production, comprehending the molecular basis for lipid and glucose metabolism in domestic animals is a significant issue. In avian species, lipids, especially triglycerides, are thought to be stored in adipocytes, hepatocytes, and growing oocytes. Excessive accumulation of lipids in the adipose tissue of broilers is a major concern for producers, because excessive fat deposits result in lower meat yields. In 2000, we reported the cloning of three chicken PPAR subtype genes (α, β, and γ) from cDNA libraries prepared from 2.5-day-old chicken embryos and adult adipose tissue [1]. For cPPARγ, amino acid residues predicted for phosphorylation by MAP kinase [2] (Ser82 in cPPARγ) and Cdk5 [3] (Ser243 in cPPARγ) were conserved between mammals and chicken PPARγ. Moreover, predicted SUMOylation target residues (Lys77 and Lys365 in cPPARγ) were also conserved in cPPARγ [4]. This shows the possibility that the transcriptional activity of cPPARγ regulates growth factors and that cPPARγ activation has an anti-inflammatory effect. However, we were unable to isolate the PPARγ2 splicing variant identified in mammals [5, 6]. This variant is likely
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