Expression patterns of the chicken peroxisome proliferator-activated receptors (PPARs) during the development of the digestive organs

Molecular expression of clock genes in central and peripheral tissues of white-rumped munia (Lonchura striata)

To synchronize with the fluctuating environment, organisms have evolved an endogenous time tracking mechanism referred to as the biological clock(s). This clock machinery has been identified in almost all cells of vertebrates and categorized as central and peripheral clocks. In birds, three independent circadian clocks have been identified in the hypothalamus, the pineal and the retina which interact and generate circadian time at a functional level. However, there is a limited knowledge of molecular clockwork and integration between central and peripheral clocks in birds. Therefore, we studied the daily expression of clock genes (Bmal1, Clock, Per2, Cry1, Npas2, Rev-Erbα, E4bp4, Pparα, Hlf and Tef) in three central circadian clocks (hypothalamus, pineal and retina), other brain areas (cerebellum, optic tectum and telencephalon) and in the peripheral tissues (liver, intestine, muscle and blood) of white-rumped munia. Adult birds were exposed to equinox photoperiod (12 L:12D) for 2 weeks and were then sampled (N = 5 per time point) at six-time points (ZT1, ZT5, ZT9, ZT13, ZT17 and ZT21). Daily expressions of clock genes were studied using qPCR. We observed daily variations and tissue-specific expression patterns for clock genes. These results are consistent with the autoregulatory circadian feedback loop proposed for the mammalian system and thus suggest a conserved tissue-level circadian time generation in white-rumped munia.

Should I Lay or Should I Grow: Photoperiodic Versus Metabolic Cues in Chickens

While photoperiod has been generally accepted as the primary if not the exclusive cue to stimulate reproduction in photoperiodic breeders such as the laying hen, current knowledge suggests that metabolism, and/or body composition can also play an influential role to control the hypothalamic-pituitary gonadal (HPG)-axis. This review thus intends to first describe how photoperiodic and metabolic cues can impact the HPG axis, then explore and propose potential common pathways and mechanisms through which both cues could be integrated. Photostimulation refers to a perceived increase in day-length resulting in the stimulation of the HPG. While photoreceptors are present in the retina of the eye and the pineal gland, it is the deep brain photoreceptors (DBPs) located in the hypothalamus that have been identified as the potential mediators of photostimulation, including melanopsin (OPN4), neuropsin (OPN5), and vertebrate-ancient opsin (VA-Opsin). Here, we present the current state of knowledge surrounding these DBPs, along with their individual and relative importance and, their possible downstream mechanisms of action to initiate the activation of the HPG axis. On the metabolic side, specific attention is placed on the hypothalamic integration of appetite control with the stimulatory (Gonadotropin Releasing Hormone; GnRH) and inhibitory (Gonadotropin Inhibitory Hormone; GnIH) neuropeptides involved in the control of the HPG axis. Specifically, the impact of orexigenic peptides agouti-related peptide (AgRP), and neuropeptide Y (NPY), as well as the anorexigenic peptides pro-opiomelanocortin (POMC), and cocaine-and amphetamine regulated transcript (CART) is reviewed. Furthermore, beyond hypothalamic control, several metabolic factors involved in the control of body weight and composition are also presented as possible modulators of reproduction at all three levels of the HPG axis. These include peroxisome proliferator-activated receptor gamma (PPAR-γ) for its impact in liver metabolism during the switch from growth to reproduction, adiponectin as a potential modulator of ovarian development and follicular maturation, as well as growth hormone (GH), and leptin (LEP).

Lycopene supplementation regulates the gene expression profile and fat metabolism of breeding hens

This study investigated the effects of lycopene on the gene expression profile and expression of genes related to fat metabolism of Xinghua breeding hens. Seven hundred and twenty healthy breeding hens were randomly assigned to four treatments; each treatment was replicated six times with 30 hens each. Broken rice and soybean meal were adopted for the basal diet and added with 0 (control group), 20, 40 and 80 mg/kg lycopene respectively. Gene expression profile of the liver induced by lycopene and expression of genes related to fat metabolism in hens liver and intestine were analysed after 42-day feeding trial including 7-day pre-feeding period and 35-day formal period. The genes involved in fat metabolism were analysed, and we found that lycopene significantly increased the expression of PGC1α, PPARα, RXRα and RARα in the liver, PPARγ, RXRα and RXRγ in the jejunum, and RARα in the duodenum (p < .05); reduced the expression of FABP1 and FABP10 in the liver, and FATP4 in the jejunum (p < .05). By analysing gene expression profile, 158 differentially expressed genes (DEGs) including 69 up-regulated genes and 89 down-regulated genes were obtained between control group and 40 mg/kg group. KEGG pathway analysis was performed on all DEGs, and 5 pathways were obtained. In conclusion, lycopene can affect the expression of related genes, and this may be one of the reasons that lycopene can regulate fat metabolism.

Peroxisome proliferator-activated receptor gamma (PPARγ) in yellow catfish Pelteobagrus fulvidraco: molecular characterization, mRNA expression and transcriptional regulation by insulin in vivo and in vitro

Peroxisome proliferator-activated receptor gamma (PPARγ) is ligand-inducible transcription factor and has important roles in lipid metabolism, cell proliferation and inflammation. In the present study, yellow catfish Pelteobagrus fulvidraco PPARγ cDNA was isolated from liver by RT-PCR and RACE, and its molecular characterization and transcriptional regulation by insulin in vivo and in vitro were determined. The generation of PPARγ1 and PPARγ2 was due to alternative promoter of PPARγ gene. PPARγ1 and PPARγ2 mRNA covered 2426 bp and 2537 bp, respectively, with an open reading frame (ORF) of 1584 bp encoding 527 amino acid residues. Yellow catfish PPARγ gene was organized in a manner similar to that of their mammalian homologs, implying a modular organization of the protein's domains. A comparison between the yellow catfish PPARγ amino acid sequence and the correspondent sequences of several other species revealed the identity of 55-76.2%. Two PPARγ transcripts (PPARγ1 and PPARγ2) mRNAs were expressed in a wide range of tissues, but the abundance of each PPARγ mRNA showed the tissue- and developmental stage-dependent expression patterns. Intraperitoneal injection of insulin in vivo significantly stimulated the mRNA expression of total PPARγ and PPARγ1, but not PPARγ2 in the liver of yellow catfish. In contrast, incubation of hepatocytes with insulin in vitro increased the mRNA levels of PPARγ1, PPARγ2 and total PPARγ. To our knowledge, for the first time, the present study provides evidence that PPARγ1 and PPARγ2 are differentially expressed with and among tissues during different developmental stages and also regulated by insulin both in vivo and in vitro, which serves to increase our understanding on PPARγ physiological function in fish.

Physiological functions of peroxisome proliferator-activated receptor β

The peroxisome proliferator-activated receptors, PPARα, PPARβ, and PPARγ, are a family of transcription factors activated by a diversity of molecules including fatty acids and fatty acid metabolites. PPARs regulate the transcription of a large variety of genes implicated in metabolism, inflammation, proliferation, and differentiation in different cell types. These transcriptional regulations involve both direct transactivation and interaction with other transcriptional regulatory pathways. The functions of PPARα and PPARγ have been extensively documented mainly because these isoforms are activated by molecules clinically used as hypolipidemic and antidiabetic compounds. The physiological functions of PPARβ remained for a while less investigated, but the finding that specific synthetic agonists exert beneficial actions in obese subjects uplifted the studies aimed to elucidate the roles of this PPAR isoform. Intensive work based on pharmacological and genetic approaches and on the use of both in vitro and in vivo models has considerably improved our knowledge on the physiological roles of PPARβ in various cell types. This review will summarize the accumulated evidence for the implication of PPARβ in the regulation of development, metabolism, and inflammation in several tissues, including skeletal muscle, heart, skin, and intestine. Some of these findings indicate that pharmacological activation of PPARβ could be envisioned as a therapeutic option for the correction of metabolic disorders and a variety of inflammatory conditions. However, other experimental data suggesting that activation of PPARβ could result in serious adverse effects, such as carcinogenesis and psoriasis, raise concerns about the clinical use of potent PPARβ agonists.

Structural Features and Transcriptional Activity of Chicken PPARs (α, β, and γ)

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.

Transcription of genes involved in fat metabolism in chicken embryos exposed to the peroxisome proliferator-activated receptor alpha (PPARα) agonist GW7647 or to perfluorooctane sulfonate (PFOS) or perfluorooctanoic acid (PFOA)

Perfluoroalkyl acids (PFAAs) such as perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) are developmental toxicants in various animal classes, including birds. Both compounds interact with peroxisome proliferator-activated receptors (PPARs), but it is not known whether activation of PPARs is involved in their embryo toxicity in birds. We exposed chicken embryos via egg injection at a late developmental stage to GW7647, a potent PPARα agonist in mammals, and to PFOS or PFOA. Mortality was induced by PFOS and PFOA but not by GW7647. Transcripts of a number of genes activated by PPARα agonists in mammals were analyzed in liver and kidney of 18-day-old embryos. Several of the genes were induced in both liver and kidney following exposure to GW7647. Treatment with PFOA resulted in induction of acyl-coenzyme A oxidase mRNA in liver, whereas none of the genes were significantly induced by PFOS treatment. No up-regulation of gene transcription was found in kidney following treatment with PFOS or PFOA. Principal component analysis showed that PFOA caused an mRNA expression pattern in liver more similar to the pattern induced by GW7647 than PFOS did. Our findings do not support that the embryo mortality by PFOS and PFOA in chicken embryos involves PPARα activation.

Effects of cold stress on the messenger ribonucleic acid levels of peroxisome proliferator-activated receptor-{gamma} in spleen, thymus, and bursa of Fabricius of chickens

This study was to investigate the expression trait of the peroxisome proliferator-activated receptor-gamma (PPAR-gamma) gene and the effect of cold stress on the mRNA levels of PPAR-gamma in spleen, thymus, and bursa of Fabricius of chickens. Eighty-four 1-d-old male chickens were randomly allocated to 12 groups (7 chickens per group). There was 1 control group and 5 treatment groups for acute cold stress and 3 control groups and 3 treatment groups for chronic cold stress. Chickens were maintained in our animal facility, kept under a 16L:8D cycle and temperature (30 +/- 2 degrees C), and given free access to standard chow and water. The cold stress was initiated when the birds were 15 d of age, with the duration of the acute cold stress being 1, 3, 6, 12, and 24 h, and the chronic cold stress was 5, 10, and 20 d, respectively. Cold stress temperature was 12 +/- 1 degrees C. Spleen, thymus, and bursa of Fabricius were collected for the assessment of the mRNA levels by real-time PCR after stress termination. The results showed that the PPAR-gamma gene is expressed in spleen, thymus, and bursa of Fabricius, and its expression level is different in different tissues and at different ages. Acute cold stress significantly decreased (P < 0.05) the mRNA levels of the PPAR-gamma gene of spleen and thymus in all treatment groups and significantly increased (P < 0.05) the mRNA levels of the PPAR-gamma gene of bursa of Fabricius in all treatment groups. Compared with the corresponding control groups, chronic cold stress resulted in a significant increase (P < 0.05) of the mRNA levels of the PPAR-gamma gene in spleen and a significant decrease (P < 0.05) of the mRNA levels of the PPAR-gamma gene in thymus and bursa of Fabricius. The results indicate that the PPAR-gamma gene is expressed in all 3 immune organs and has different expression traits. The magnitude and direction of change in PPAR-gamma gene expression differs with the type of cold stress applied and also varies by tissue.

The differential expression of peroxisome proliferators-activated receptors in various duck tissues

Peroxisome proliferators-activated receptors (PPARs) plays important role in regulate a variety of target genes which involves in lipid metabolism. In the present study, 1,430 bp of PPARalpha and 1,650 bp of PPARgamma in Peking duck (Anas platyrhynchos) were cloned by reverse transcription (RT)-PCR. The cloned sequences of PPARalpha and PPARgamma were highly conserved, although relevant changes with respect to human, mouse, chicken, and goose were identified. Real-time quantitative RT-PCR was used to determine if the PPARalpha and PPARgamma were expressed in different tissues of male and female Peking ducks. The expression of PPARalpha and PPARgamma were widely distributed in all examined tissues. The expression level of PPARalpha was highest in liver and lowest in kidney in male and female ducks. And it was highest in abdominal fat and lowest in small intestine of PPARgamma in male and female ducks.

Fatty acids but not dexamethasone are essential inducers for chick adipocyte differentiation in vitro

The present study was carried out to clarify the direct effect of fatty acids (FAs) on chick (Gallus gallus) adipocyte differentiation in the absence of dexmethasone (DEX), a commonly used as strong inducer for adipocyte differentiation. Adipocyte differentiation was initiated by maintaining confluent cell in serum-free medium supplemented with FAs. Upon exposure to FAs, glycerol-3-phosphate dehydrogenase activity (GPDH) as adipocyte differentiation marker rapidly increased, and was significantly higher in chick adipocyte than in control cell. The morphology of the FAs-treated cell changed from fibroblast-like to polygon, and the cells accumulated many cytoplasmic lipid droplets as estimated by Oil red O staining. Neither insulin nor bovine serum albumin, as substitutes for serum, had an effect on chick adipocyte differentiation. The FAs-treated cell had a higher protein and mRNA expression levels for peroxisome proliferator-activated receptor-gamma (PPARgamma), a master regulator of differentiation, compared with untreated cell. In FAs-treated cell, the mRNA expression levels of adipocyte-specific genes, such as CCAAT/enhancer binding protein-alpha (C/EBP alpha) and adipocyte fatty acid-binding protein (aP2) were higher than in control cell. These results indicated that FAs, but not DEX, are essential inducers for chick adipocyte differentiation by elevating PPARgamma expression.

Molecular analysis of endoderm regionalization

We have engaged in a number of studies in our laboratory that have focused on the molecular mechanisms underlying gut formation, with particular attention being paid to the establishment of regional differences found in the entire gut and within each digestive organ. We have found from our analyses that the presumptive fate of the endoderm in the embryos of vertebrates is determined quite early during development, but the realization of this fate often requires molecular cues from the neighboring tissues such as the lateral plate mesoderm and the mesenchyme derived from it. The mesenchyme seems often to exert instructive or supportive induction effects and, in some cases, a completely inhibitory role during the differentiation of the endodermal epithelium. In addition, many reports on the formation of the stomach, intestine, liver and salivary gland in vertebrates, and of Drosophila gut, all indicate that the morphogenesis and cytodifferentiation of these organs are regulated by the regulated expression of genes encoding growth factors and transcription factors. We have further shown that the epithelium can regulate the differentiation of the mesenchyme into the connective tissue and the smooth muscle layers, thus demonstrating the occurrence of literally interactive processes in the development of the digestive organs.

Expression profile of myostatin mRNA during the embryonic organogenesis of domestic chicken (Gallus gallus domesticus)

Myostatin is a potent growth and differentiation factor involved in skeletal muscle tissue formation in vertebrates. However, recent studies in chicken embryo suggested that the myostatin was expressed even before the establishment of myogenic lineage. No studies have thus far been reported in birds to define the role of myostatin during the embryonic organogenesis. The present experiment was designed for studying the expression profiles of myostatin mRNA in the chicken liver, heart, brain, and intestine during their morphogenesis, using real-time PCR. The myostatin mRNA expression was significantly upregulated in liver during E15-E18. Similar results were observed during the development of chicken heart. In brain, the expression of myostatin was upregulated from E4 onwards. In intestine, the expression of myostatin was significantly increased many folds on E9-E18. Therefore, the increase in myostatin expression might be related to the growth of liver and heart on days E12-E18; morphogenesis and growth of brain during E15-E18; and morphogenesis and differentiation of intestine during E9-E18. In the present study, the tissue-specific expression of myostatin gene in chicken is similar to fishes, but different from that in mammals. Further, the inspection of chicken genome also suggested that there is no differentiation of GDF-8 and -11. A recent finding suggests that the chicken myostatin gene is closely related to mammals than fishes. Therefore, we propose that the chicken myostatin gene might have diverged in its function between teleosts and mammals. Indeed it is possible that its function might have only become fully differentiated to serve as a control of muscle mass in mammals.