Ji et al. BMC Genomics 2012, 13:441 http://www.biomedcentral.com/1471-2164/13/441 Background The domestic chicken provides a widespread and relatively inexpensive source of dietary protein for humans. In addition to its role as a food animal, the chicken has a long history as a valuable model research organism [1]. These dual considerations led to the selection of chicken as the first agricultural animal model to be sequenced at the gen- ome level [2]. While chickens have been used heavily for studies of developmental biology and immunology, a num- ber of traits make them a viable model for studies of adi- pose biology, obesity and insulin resistance. Commercial broiler chickens, in particular, rapidly accumulate excess adipose tissue as a result of genetic selection for growth and are considered “obese” relative to leaner egg-laying or wild strains of chickens(rev. in [3]). Chickens mimic the early stage of type 2 diabetes in humans, exhibiting both hyperglycemia (up to 200 mg/dL in the fasting state) and resistance to exogenous insulin [4,5]. Like humans, but un- like rodents or pigs, chickens rely on liver rather than adi- pose tissue for the majority of de novo lipid synthesis [6-8]. Most metabolic genes are conserved with humans, and a number of the quantitative trait loci (QTLs) that have been linked to fatness in chickens contain genes implicated in human susceptibility to obesity or diabetes [9]. Chickens also represent a model for studying mechanisms of adipo- cyte hyperplasia during development, a process that may exacerbate adult obesity. During at least the first several weeks after hatch, chicken adipose tissue expands more through adipocyte hyperplasia than hypertrophy, and an early increase in adipocyte number is a common feature of some lines genetically selected for excess adiposity [10,11]. Finally, the egg presents opportunities to directly manipu- late the developmental milieu and study the consequences on adipose metabolism via in ovo injection. Relatively little is known about regulation of adipose tis- sue deposition and metabolism in chicken. Because of its relative importance in lipogenesis, most studies have fo- cused on the role of liver in adipose expansion. Several genetic lines of fat and lean chickens have been developed through phenotypic selection, most of which have both ele- vated plasma levels of very low density lipoprotein (VLDL) and lower levels of plasma glucose, reflecting the import- ance of hepatic lipogenesis and glucose consumption in fat accretion. Reciprocally, phenotypic selection for low plasma glucose simultaneously selects for fatness [12]. Both chicken and mammalian adipocytes develop through a sequence of molecular triggers including activation of CCAAT-enhancer-binding protein alpha (CEBPα) and per- oxisome proliferator-activated receptor gamma (PPARγ) [13]. A clear point of divergence, however, is their respon- siveness to insulin. Unlike in mammals, insulin has min- imal effect on glucose uptake in chicken adipose tissue [14]. In fact, an avian homolog of the insulin-sensitive glu- cose transporter GLUT4 has not been identified in the Page 2 of 16 current chicken genome database. Insulin does, however, stimulate uptake of acetate, which is the preferred substrate for de novo lipogenesis in chicken adipocytes, although the magnitude of the effect is relatively modest [15]. Insulin signaling appears to proceed through tissue specific cas- cades in chicken metabolic tissues. In liver, insulin elicits a signaling cascade that parallels the response in mammals, including tyrosine phosphorylation of insulin receptor β-subunit (IRβ), insulin receptor substrate-1 (IRS-1) and Src homology 2 domain-containing substrate (Shc) and ac- tivation of phosphatidylinositol 3-kinase (PI3K) [16,17]. The situation in skeletal muscle is more complex. Tyrosine phosphorylation of IRβ and IRS-1 and PI3K activity are not regulated by insulin, whereas events downstream of PI3K (e.g. Akt and P70S6K activation) are accordingly sensitive [18]. We recently reported that insulin also does not elicit a classical IRβ initiated cascade in chicken adipose tissue, in- cluding the downstream steps of Akt and P70S6K activa- tion [19]. Insulin also does not inhibit lipolysis in chicken adipose tissue; glucagon, is the primary lipolytic hormone (rev. in [20]). In the present study we simultaneously characterized the effects of a short term (5 hours) fast or neutralization of insulin action (5 hours) on adipose tissue of young (16–17 day-old), fed commercial broiler chickens. The goals of this study were two-fold. First, we sought to iden- tify pathways activated by feed restriction, reasoning that they may highlight potential strategies for control of fatness through either genetic selection or improved management practices. Simultaneously, we sought to understand the contribution of insulin, if any, into chicken adipose physi- ology. No experimental model of diabetes exist in chicken: total pancreatectomies are not achievable, and alloxan and streptozotocin are inefficient at destroying pancreatic chicken beta-cells (rev. in [5]). The two treatments were compared to distinguish potential insulin-specific changes from those that could be mimicked by fasting through changes in nutrient availability. Both treatments were shown previously to elicit significant alterations in several plasma metabolic and endocrine parameters [18]; in the studies reported herein, samples of abdominal adipose tis- sue were issued from the same experiment. Tissue metabo- lomics was combined with microarrays to bridge the gap between gene expression, metabolic and physiological responses, and to identify the composite effects of both fasting and insulin deprivation on chicken adipose tissue. Results Expression levels of a total of 2016 genes were signifi- cantly altered by fasting and/or insulin neutralization when compared to fed controls based on an FDR adjusted p-value < 0.05 (Additional file 1; Figure 1A). Sixty-nine percent of these genes showed a fold-change ≥ |1.5| (Figure 1B). The majority of changes in expression