Local Agouti Signaling Protein/Melanocortin Signaling System that Possibly Regulates Lipid Metabolism in Adipose Tissues of Chickens

Characterization of the chicken melanocortin 5 receptor and its potential role in regulating hepatic glucolipid metabolism

Melanocortin receptors (MC1R-MC5R) and their accessory proteins (MRAPs) are involved in a variety of physiological processes, including pigmentation, lipolysis, adrenal steroidogenesis, and immunology. However, the physiological roles of MC5R are rarely characterized in vertebrates, particularly in birds. In this work, we cloned the full-length cDNA of chicken MC5R and identified its core promoter region. Functional studies revealed that cMC5R was more sensitive to ACTH/α-MSH than β-MSH/γ-MSH, and was coupled to the cAMP/PKA signaling pathway. We demonstrated that MRAP2 decreased MC5R sensitivity to α-MSH, whereas MRAP1 did not have a similar effect, and that both MRAPs significantly reduced MC5R expression on the cell membrane surface. Transcriptome and qPCR data showed that both MRAP1 and MC5R were highly expressed in chicken liver. Additionally, we observed that ACTH might increase hepatic glucose production and decrease lipogenesis in primary hepatocytes, and dose-dependently downregulated the expression levels of ELOVL6 and THRSPA genes. These findings indicated that ACTH may act directly on hepatocytes to regulate glucolipid metabolism, which will help to understand the function of MC5R in avian.

Comparative Transcriptome Analysis of Milk Somatic Cells During Lactation Between Two Intensively Reared Dairy Sheep Breeds

In dairy sheep industry, milk production dictates the value of a ewe. Milk production is directly related to the morphology and physiology of the mammary gland; both being designated targets of breeding strategies. Although within a flock breeding parameters are mutual, large differences in milk production among individual ewes are usually observed. In this work, we tested two of the most productive dairy sheep breeds reared intensively in Greece, one local the Chios breed and one foreign the Lacaune breed. We used transcriptome sequencing to reveal molecular mechanisms that render the mammary gland highly productive or not. While highly expressed genes (caseins and major whey protein genes) were common among breeds, differences were observed in differentially expressed genes. ENSOARG00000008077, as a member of ribosomal protein 14 family, together with LPCAT2, CCR3, GPSM2, ZNF131, and ASIP were among the genes significantly differentiating mammary gland's productivity in high yielding ewes. Gene ontology terms were mainly linked to the inherent transcriptional activity of the mammary gland (GO:0005524, GO:0030552, GO:0016740, GO:0004842), lipid transfer activity (GO:0005319) and innate immunity (GO:0002376, GO:0075528, GO:0002520). In addition, clusters of genes affecting zinc and iron trafficking into mitochondria were highlighted for high yielding ewes (GO:0071294, GO:0010043). Our analyses provide insights into the molecular pathways involved in lactation between ewes of different performances. Results revealed management issues that should be addressed by breeders in order to move toward increased milk yields through selection of the desired phenotypes. Our results will also contribute toward the selection of the most resilient and productive ewes, thus, will strengthen the existing breeding systems against a spectrum of environmental threats.

Screening and analysis of agouti signaling protein interaction partners in Pelodiscus sinensis suggests a role in lipid metabolism

Agouti signaling protein (ASP) is a secreted paracrine protein that has been widely reported to function in melanogenesis and obesity and could potentially be a core protein that regulates the color and fatty phenotype of P. sinensis. In this study, we screened out interacting proteins of ASP by combined co-immunoprecipitation mass spectrometry (CoIP-MS), yeast two hybrid (Y2H) analysis, and computational predictions. We performed docking of ASP with its well-known receptor melanocortin receptor 4 (MC4R) to predict the binding capacity and to screen out actual ASP interacting proteins, CoIP-MS was performed where identified 32 proteins that could bind with ASP and Y2H confirmed seven proteins binding with ASP directly. CoIP-MS and Y2H screening results including PPI prediction revealed that vitronectin (VTN), apolipoprotein A1 (APOA1), apolipoprotein B (APOB), and filamin B (FLNB) were the key interacting proteins of ASP. VTN, APOA1, and APOB are functional proteins in lipid metabolism and various skin disorders, suggesting ASP may function in lipid metabolism through these partners. This study provided protein-protein interaction information of ASP, and the results will promote further research into the diverse roles of ASP, as well as its binding partners, and their function in different strains of P. sinensis.

TRIENNIAL GROWTH AND DEVELOPMENT SYMPOSIUM: Factors influencing bovine intramuscular adipose tissue development and cellularity

Appearance, distribution, and amount of intramuscular fat (IMF), often referred to as marbling, are highly variable and depend on environmental and genetic factors. On the molecular level, the concerted action of several drivers, including hormones, receptors, transcription factors, etc., determines where clusters of adipocytes arise. Therefore, the aim of future studies remains to identify such factors as biological markers of IMF to increase the ability to identify animals that deposit IMF early in age to increase efficiency of high-quality meat production. In an attempt to unravel the cellular development of marbling, we investigated the abundance of markers for adipogenic differentiation during fattening of cattle and the transcriptome of muscle and dissected IMF. Markers of different stages of adipogenic differentiation are well known from cell culture experiments. They are usually transiently expressed, such as delta-like homolog 1 (DLK1) that is abundant in preadipocytes and absent during differentiation to mature adipocytes. It is even a greater challenge to detect those markers in live animals. Within skeletal muscles, hyperplasia and hypertrophy of adipocytes can be observed throughout life. Therefore, development of marbling requires, on the cellular level, recruitment, proliferation, and differentiation of adipogenic cells to store excess energy in the form of lipids in new cells. In a recent study, we investigated the localization and abundance of early markers of adipogenic differentiation, such as DLK1, in bovine muscle tissue. An inverse relationship between IMF content and number of DLK1-positive cells in bovine muscle was demonstrated. Considering the cellular environment of differentiating adipocytes in muscle and the secretory action of adipocytes and myocytes, it becomes obvious that cross talk between cells via adipokines and myokines may be important for IMF development. Secreted proteins can act on other cells, inhibiting or stimulating their function via autocrine and paracrine actions. Such factors with potential influence on IMF, among them, agouti signaling protein and thrombospondin 4, were identified in transcriptome analyses and further investigated. Furthermore, results from transcriptome analysis indicate involvement of genes that are not directly related to adipogenesis and lipid metabolism, providing new candidates for future research.

MC1R variants affect the expression of melanocortin and melanogenic genes and the association between melanocortin genes and coloration

The melanocortin-1 receptor (MC1R) gene influences coloration by altering the expression of genes acting downstream in the melanin synthesis. MC1R belongs to the melanocortin system, a genetic network coding for the ligands that regulate MC1R and other melanocortin receptors controlling different physiological and behavioural traits. The impact of MC1R variants on these regulatory melanocortin genes was never considered, even though MC1R mutations could alter the influence of these genes on coloration (e.g. by decreasing MC1R response to melanocortin ligands). Using barn owl growing feathers, we investigated the differences between MC1R genotypes in the (co)expression of six melanocortin and nine melanogenic-related genes and in the association between melanocortin gene expression and phenotype (feather pheomelanin content). Compared to the MC1R rufous allele, responsible for reddish coloration, the white allele was not only associated with an expected lower expression of melanogenic-related genes (TYR, TYRP1, OCA2, SLC45A2, KIT, DCT) but also with a lower MC1R expression and a higher expression of ASIP, the MC1R antagonist. More importantly, the expression of PCSK2, responsible for the maturation of the MC1R agonist, α-melanocyte-stimulating hormone, was positively related to pheomelanin content in MC1R white homozygotes but not in individuals carrying the MC1R rufous allele. These findings indicate that MC1R mutations not only alter the expression of melanogenic-related genes but also the association between coloration and the expression of melanocortin genes upstream of MC1R. This suggests that MC1R mutations can modulate the regulation of coloration by the pleiotropic melanocortin genes, potentially decoupling the often-observed associations between coloration and other phenotypes.

Melanosome evolution indicates a key physiological shift within feathered dinosaurs

Inference of colour patterning in extinct dinosaurs has been based on the relationship between the morphology of melanin-containing organelles (melanosomes) and colour in extant bird feathers. When this relationship evolved relative to the origin of feathers and other novel integumentary structures, such as hair and filamentous body covering in extinct archosaurs, has not been evaluated. Here we sample melanosomes from the integument of 181 extant amniote taxa and 13 lizard, turtle, dinosaur and pterosaur fossils from the Upper-Jurassic and Lower-Cretaceous of China. We find that in the lineage leading to birds, the observed increase in the diversity of melanosome morphologies appears abruptly, near the origin of pinnate feathers in maniraptoran dinosaurs. Similarly, mammals show an increased diversity of melanosome form compared to all ectothermic amniotes. In these two clades, mammals and maniraptoran dinosaurs including birds, melanosome form and colour are linked and colour reconstruction may be possible. By contrast, melanosomes in lizard, turtle and crocodilian skin, as well as the archosaurian filamentous body coverings (dinosaur 'protofeathers' and pterosaur 'pycnofibres'), show a limited diversity of form that is uncorrelated with colour in extant taxa. These patterns may be explained by convergent changes in the key melanocortin system of mammals and birds, which is known to affect pleiotropically both melanin-based colouration and energetic processes such as metabolic rate in vertebrates, and may therefore support a significant physiological shift in maniraptoran dinosaurs.

Quantity of glucose transporter and appetite-associated factor mRNA in various tissues after insulin injection in chickens selected for low or high body weight

Chickens from lines selected for low (LWS) or high (HWS) body weight differ by 10-fold in body weight at 56 days old with differences in food intake, glucose regulation, and body composition. To evaluate if there are differences in appetite-regulatory factor and glucose transporter ( GLUT) mRNA that are accentuated by hypoglycemia, blood glucose was measured, and hypothalamus, liver, pectoralis major, and abdominal fat collected at 90 days of age from female HWS and LWS chickens, and reciprocal crosses, HL and LH, at 60 min after intraperitoneal injection of insulin. Neuropeptide Y ( NPY) and receptor ( NPYR) subtypes 1 and 5 mRNA were greater in LWS compared with HWS hypothalamus ( P < 0.05), but greater in HWS than LWS in fat ( P < 0.05). Expression of NPYR2 was greater in LWS than HWS in pectoralis major ( P < 0.05). There was greater expression in HWS than LWS for GLUT1 in hypothalamus and liver ( P < 0.05), GLUT2 in fat and liver ( P < 0.05), and GLUT9 in liver ( P < 0.05). Insulin was associated with reduced blood glucose in all populations ( P < 0.05) and reduced mRNA of insulin receptor ( IR) and GLUT 2 and 3 in liver ( P < 0.05). There was heterosis for mRNA, most notably NPYR1 (−78%) and NPYR5 (−81%) in fat and GLUT2 (−70%) in liver. Results suggest that NPY and GLUTs are associated with differences in energy homeostasis in LWS and HWS. Reduced GLUT and IR mRNA after insulin injection suggest a compensatory mechanism to prevent further hypoglycemia.

Conserved distal promoter of the agouti signaling protein (ASIP) gene controls sexual dichromatism in chickens

Brilliant plumage is typical of male birds, thus sexual plumage dichromatism is seen in many avian species; however, the molecular mechanism underlying this remains unclear. The agouti signaling protein (ASIP) is a paracrine factor that stimulates yellow/red pigment (pheomelanin) synthesis and inhibits black/brown pigment (eumelanin) synthesis in follicular melanocytes. In mammals, the distal promoter of the ASIP gene acts exclusively on the ventral side of the body to create a countershading pigmentation pattern by stimulating pheomelanin synthesis in the ventrum. Here, we examined the role of the distal ASIP promoter in controlling estrogen-dependent sexual dichromatism in chickens. Reverse-transcription polymerase chain reaction analyses revealed that ASIP class 1 mRNAs transcribed by the distal promoter were expressed exclusively on the ventral side of chicks and adult females displaying countershading. In showy adult males, the ASIP class 1 mRNAs were expressed in gold-colored ornamental feathers grown on the back. In the presence of estrogen, males molted into female-like plumage and ASIP class 1 mRNAs expression was altered to female patterns. These results suggest that the distal ASIP promoter produces countershading in chicks and adult females, similar to the ventral-specific ASIP promoter in mammals. In addition, the class 1 promoter plays an important role for creating sexual plumage dichromatism controlled by estrogen. This is the first evidence for a pigmentation gene having been modified in its expression during evolution to develop phenotypic diversity between individuals of different sexes.

Agouti revisited: transcript quantification of the ASIP gene in bovine tissues related to protein expression and localization

Beside its role in melanogenesis, the agouti signaling protein (ASIP) has been related to obesity. The potentially crucial role in adipocyte development makes it a tempting candidate for economic relevant, fat related traits in farm animals. The objective of our study was to characterize the mRNA expression of different ASIP transcripts and of putative targets in different bovine tissues, as well as to study consequences on protein abundance and localization. ASIP mRNA abundance was determined by RT-qPCR in adipose and further tissues of cattle representing different breeds and crosses. ASIP mRNA was up-regulated more than 9-fold in intramuscular fat of Japanese Black cattle compared to Holstein (p<0.001). Further analyses revealed that a transposon-derived transcript was solely responsible for the increased ASIP mRNA abundance. This transcript was observed in single individuals of different breeds indicating a wide spread occurrence of this insertion at the ASIP locus in cattle. The protein was detected in different adipose tissues, skin, lung and liver, but not in skeletal muscle by Western blot with a bovine-specific ASIP antibody. However, the protein abundance was not related to the observed ASIP mRNA over-expression. Immuno-histochemical analyses revealed a putative nuclear localization of ASIP additionally to the expected cytosolic signal in different cell types. The expression of melanocortin receptors (MCR) 1 to 5 as potential targets for ASIP was analyzed by RT-PCR in subcutaneous fat. Only MC1R and MC4R were detected indicating a similar receptor expression like in human adipose tissue. Our results provide evidence for a widespread expression of ASIP in bovine tissues at mRNA and, for the first time, at protein level. ASIP protein is detectable in adipocytes as well as in further cells of adipose tissue. We generated a basis for a more detailed investigation of ASIP function in peripheral tissues of various mammalian species.

Elaborate color patterns of individual chicken feathers may be formed by the agouti signaling protein

Hair and feather pigmentation is mainly determined by the distribution of two kinds of melanin, eumelanin and pheomelanin, which produce brown to black and yellow to red colorations, respectively. The agouti signaling protein (ASIP) acts as an antagonist or an inverse agonist of the melanocortin 1 receptor (MC1R), a G protein-coupled receptor for α-melanocyte-stimulating hormone (α-MSH). This antagonism of the MC1R by ASIP on melanocytes initiates a switch of melanin synthesis from eumelanogenesis to pheomelanogenesis in mammals. In the present study, we isolated multiple ASIP mRNA variants generated by alternative splicing and promoters in chicken feather follicles. The mRNA variants showed a discrete tissue distribution. However, mRNAs were expressed predominantly in the feather pulp of follicles. Paralleling mRNA distribution, ASIP immunoreactivity was observed in feather pulp. Interestingly, ASIP was stained with pheomelanin but not eumelanin in pulp areas that face developing barbs. We suggest that the elaborate color pattern of individual feathers is formed in part by the antagonistic action of ASIP that is produced by multiple mRNA variants in chicken feather follicles.

Feather follicles express two classes of pro-opiomelanocortin (POMC) mRNA using alternative promoters in chickens

Feather coloration in chickens mainly depends on melanin produced by melanocytes located in the feather follicles. The melanocortin 1 receptor (MC1R) on follicular melanocytes regulates melanin synthesis; however, the source of the melanocortins that interact with the receptors remains unclear. In this study, we examine the potential expression of melanocortins and characterize the mRNAs for the precursor pro-opiomelanocortin (POMC) in chicken feather follicles. Reverse transcription-polymerase chain reaction (RT-PCR) revealed the expression of mRNAs for POMC, prohormone convertase 1 (PC1) and PC2, and western blotting detected adrenocorticotropic hormone (ACTH)-related products of POMC processing in feather follicles, suggesting that melanocortins are produced locally in the tissues of chickens. A combination of 5'RACE (rapid amplification of cDNA 5' end), 3'RACE and RT-PCR analyzes identified two classes of POMC mRNA, class a and class b, which encode the same full-length POMC protein but have different non-coding leader exons. Class a mRNAs were expressed specifically in feather follicles, whereas class b mRNAs were expressed in the pituitary, hypothalamus, and various peripheral tissues that we examined. Within the feather follicles, the class a mRNAs were distributed in epidermal layers from middle to distal locations, whereas the class b mRNAs were mainly expressed in pulp at proximal locations. Our findings suggest that feather pigmentation is regulated by locally produced melanocortins, and indicate that the melanocortins encoded by the different classes of POMC mRNAs may play different intra-follicular roles in chickens. This is the first report that demonstrates alternative promoter usage generating different full-length POMC mRNAs in vertebrates.