Molecular structure and chromosomal mapping of the human homolog of the agouti gene

Characterization of agouti-signaling protein (ASIP) in the bovine ovary and throughout early embryogenesis

The oocyte expresses certain genes during folliculogenesis to regulate the acquisition of oocyte competence. Oocyte competence, or oocyte quality, is directly related to the ability of the oocyte to result in a successful pregnancy following fertilization. Presently, approximately 40 % of bovine embryos will develop to the blastocyst stage in vitro. Characterization of factors regulating these processes is crucial to improve the efficiency of bovine in vitro embryo production. We demonstrated that the secreted protein, agouti-signaling protein (ASIP) is highly abundant in the bovine oocyte and aimed to characterize its spatiotemporal expression profile in the ovary and throughout early embryonic development. In addition to oocyte expression, ASIP was detected in granulosa, cumulus, and theca cells isolated from antral follicles. Both gene expression data and immunofluorescent staining indicated ASIP declines with oocyte maturation which may indicate a potential role for ASIP in the attainment of oocyte competence. Microinjection of zygotes using small interfering RNA targeting ASIP led to a 16 % reduction in the rate of development to the blastocyst stage. Additionally, we examined potential ASIP signaling mechanisms through which ASIP may function to establish oocyte developmental competence. The expression of melanocortin receptor 3 and 4 and the coreceptor attractin was detected in the oocyte and follicular cells. The addition of cortisol during in vitro maturation was found to increase significantly oocyte ASIP levels. In conclusion, these results suggest a functional role for ASIP in promoting oocyte maturation and subsequent embryonic development, potentially through signaling mechanisms involving cortisol.

Aberrant expression of agouti signaling protein (ASIP) as a cause of monogenic severe childhood obesity

Here we report a heterozygous tandem duplication at the ASIP (agouti signaling protein) gene locus causing ubiquitous, ectopic ASIP expression in a female patient with extreme childhood obesity. The mutation places ASIP under control of the ubiquitously active itchy E3 ubiquitin protein ligase promoter, driving the generation of ASIP in patient-derived native and induced pluripotent stem cells for all germ layers and hypothalamic-like neurons. The patient's phenotype of early-onset obesity, overgrowth, red hair and hyperinsulinemia is concordant with that of mutant mice ubiquitously expressing the homolog nonagouti. ASIP represses melanocyte-stimulating hormone-mediated activation as a melanocortin receptor antagonist, which might affect eating behavior, energy expenditure, adipocyte differentiation and pigmentation, as observed in the index patient. As the type of mutation escapes standard genetic screening algorithms, we rescreened the Leipzig Childhood Obesity cohort of 1,745 patients and identified four additional patients with the identical mutation, ectopic ASIP expression and a similar phenotype. Taken together, our data indicate that ubiquitous ectopic ASIP expression is likely a monogenic cause of human obesity.

Regulation of the central melanocortin system on energy balance in mammals and birds

Agouti-related protein/neuropeptide Y (AgRP/NPY) neurons promote feeding, while proopiomelanocortin/cocaine- and amphetamine-regulated transcript (POMC/CART) neurons and melanocortin receptor neurons inhibit feeding; these three types of neurons play vital roles in regulating feeding. The central melanocortin system composed of these neurons is critical for the regulation of food intake and energy metabolism. It regulates energy intake and consumption by activating or inhibiting the activities of AgRP/NPY neurons and POMC/CART neurons and then affects the feeding behaviour of animals to maintain the energy balance. Meanwhile, organisms can also positively or negatively regulate energy homeostasis through the negative feedback of the neuron system. With further studies, understanding of the process and factors involved in the energy balance regulation of mammals and birds can be improved, which will provide a favourable scientific basis to reduce costs and improve meat production in production and breeding.

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.

Molecular determinants of ACTH receptor for ligand selectivity

The adrenocorticotropic hormone (ACTH) receptor, known as the melanocortin-2 receptor (MC2R), plays a key role in regulating adrenocortical function. ACTH receptor is a subtype of the melanocortin receptor family which is a member of the G-protein coupled receptor (GPCR) superfamily. ACTH receptor has unique characteristics among MCRs. α-MSH, β-MSH, γ-MSH and ACTH are agonists for MCRs but only ACTH is the agonist for ACTH receptor. In addition, the melanocortin receptor accessory protein (MRAP) is required for ACTH receptor expression at cell surface and function. In this review, we summarized the information available on the relationship between ACTH and ACTH receptor and provide the latest understanding of the molecular basis of the ACTH receptor responsible for ligand selectivity and function.

MC1R: Front and Center in the Bright Side of Dark Eumelanin and DNA Repair

Melanin, the pigment produced by specialized cells, melanocytes, is responsible for skin and hair color. Skin pigmentation is an important protective mechanism against the DNA damaging and mutagenic effects of solar ultraviolet radiation (UV). It is acknowledged that exposure to UV is the main etiological environmental factor for all forms of skin cancer, including melanoma. DNA repair capacity is another major factor that determines the risk for skin cancer. Human melanocytes synthesize eumelanin, the dark brown form of melanin, as well as pheomelanin, which is reddish-yellow in color. The relative rates of eumelanin and pheomelanin synthesis by melanocytes determine skin color and the sensitivity of skin to the drastic effects of solar UV. Understanding the complex regulation of melanocyte function and how it responds to solar UV has a huge impact on developing novel photoprotective strategies to prevent skin cancer, particularly melanoma, the most fatal form, which originates from melanocytes. This review provides an overview of the known differences in the photoprotective effects of eumelanin versus pheomelanin, how these two forms of melanin are regulated genetically and biochemically, and their impact on the DNA damaging effects of UV exposure. Additionally, this review briefly discusses the role of paracrine factors, focusing on α-melanocortin (α-melanocyte stimulating hormone; α-MSH), in regulating melanogenesis and the response of melanocytes to UV, and describes a chemoprevention strategy based on targeting the melanocortin 1 receptor (MC1R) by analogs of its physiological agonist α-MSH.

BAC Recombineering of the Agouti Loci from Spotted Gar and Zebrafish Reveals the Evolutionary Ancestry of Dorsal-Ventral Pigment Asymmetry in Fish

Dorsoventral pigment patterning, characterized by a light ventrum and a dark dorsum, is one of the most widespread chromatic adaptations in vertebrate body coloration. In mammals, this countershading depends on differential expression of agouti-signaling protein (ASIP), which drives a switch of synthesis of one type of melanin to another within melanocytes. Teleost fish share countershading, but the pattern results from a differential distribution of multiple types of chromatophores, with black-brown melanophores most abundant in the dorsal body and reflective iridophores most abundant in the ventral body. We previously showed that Asip1 (a fish ortholog of mammalian ASIP) plays a role in patterning melanophores. This observation leads to the surprising hypothesis that agouti may control an evolutionarily conserved pigment pattern by regulating different mechanisms in mammals and fish. To test this hypothesis, we compared two ray-finned fishes: the teleost zebrafish and the nonteleost spotted gar (Lepisosteus oculatus). By examining the endogenous pattern of asip1 expression in gar, we demonstrate a dorsoventral-graded distribution of asip1 expression that is highest ventrally, similar to teleosts. Additionally, in the first reported experiments to generate zebrafish transgenic lines carrying a bacterial artificial chromosome (BAC) from spotted gar, we show that both transgenic zebrafish lines embryos replicate the endogenous asip1 expression pattern in adult zebrafish, showing that BAC transgenes from both species contain all of the regulatory elements required for regular asip1 expression within adult ray-finned fishes. These experiments provide evidence that the mechanism leading to an environmentally important pigment pattern was likely in place before the origin of teleosts.

Melanocortin 1 Receptor: Structure, Function, and Regulation

The melanocortin 1 receptor (MC1R) is a melanocytic Gs protein coupled receptor that regulates skin pigmentation, UV responses, and melanoma risk. It is a highly polymorphic gene, and loss of function correlates with a fair, UV-sensitive, and melanoma-prone phenotype due to defective epidermal melanization and sub-optimal DNA repair. MC1R signaling, achieved through adenylyl cyclase activation and generation of the second messenger cAMP, is hormonally controlled by the positive agonist melanocortin, the negative agonist agouti signaling protein, and the neutral antagonist β-defensin 3. Activation of cAMP signaling up-regulates melanin production and deposition in the epidermis which functions to limit UV penetration into the skin and enhances nucleotide excision repair (NER), the genomic stability pathway responsible for clearing UV photolesions from DNA to avoid mutagenesis. Herein we review MC1R structure and function and summarize our laboratory's findings on the molecular mechanisms by which MC1R signaling impacts NER.

Agouti signalling protein (ASIP) gene: molecular cloning, sequence characterisation and tissue distribution in domestic goose

Agouti signalling protein (ASIP) is an endogenous antagonist of melanocortin-1 receptor (MC1R) and is involved in the regulation of pigmentation in mammals. The objective of this study was to identify and characterise the ASIP gene in domestic goose. The goose ASIP cDNA consisted of a 44-nucleotide 5'-terminal untranslated region (UTR), a 390-nucleotide open-reading frame (ORF) and a 45-nucleotide 3'-UTR. The length of goose ASIP genomic DNA was 6176 bp, including three coding exons and two introns. Bioinformatic analysis indicated that the ORF encodes a protein of 130 amino-acid residues with a molecular weight of 14.88 kDa and an isoelectric point of 9.73. Multiple sequence alignments and phylogenetic analysis showed that the amino-acid sequence of ASIP was conserved in vertebrates, especially in the avian species. RT-qPCR showed that the goose ASIP mRNA was differentially expressed in the pigment deposition tissues, including eye, foot, feather follicle, skin of the back, as well as in skin of the abdomen. The expression level of the ASIP gene in skin of the abdomen was higher than that in skin of the back. Those findings will contribute to further understanding the functions of the ASIP gene in geese plumage colouring.

Effects of post-weaning diet on metabolic parameters and DNA methylation status of the cryptic promoter in the A(vy) allele of viable yellow mice

Mice carrying the A(vy) allele are epigenetic mosaics. If the majority of cells have an active (demethylated) intracisternal A particle (IAP), mice have a yellow coat color and develop adult-onset obesity and diabetes, while mice whose mosaicism predominantly reflects an inactive (methylated) IAP are pseudoagouti (brown) and less prone to metabolic disease. Brown and yellow coat color A(vy)/a post-weaning mice were placed on one of three diets [AIN, and two lower-calorie diets National Institutes of Health (NIH) and methyl-supplemented, NIHMe] to determine whether coat color, weight gain, blood glucose and methylation of hepatic IAP became altered. None of the diets altered A(vy)/a mice coat color. NIHMe did not protect against increasing obesity or the usual onset of hyperglycemia in males. Nor did it promote increased methylation of A(vy) IAP in liver tissue. By contrast, AIN, despite its higher content of fat and carbohydrate and ability to promote greater weight gains than the NIH and NIHMe diets, protected males better against hyperglycemia than either the NIH or NIHMe diets. This diet led to a significantly reduced (~50%; P = .003) average methylation state of all CpG sites within the hepatic IAP for the pseudoagouti mice. On AIN, but not on the other diets, extent of hepatic IAP methylation was negatively correlated (R = 0.97, P ≤ .001) with body weight of pseudoagouti mice. The findings indicate that post-weaning diet might influence interpretation of studies with A(vy)/a mice because IAP methylation patterns may be malleable in certain organs and influenced by post-weaning diet.

Melanocortins and the melanocortin 1 receptor, moving translationally towards melanoma prevention

Beginning in the last decade of the twentieth century, the fields of pigment cell research and melanoma have witnessed major breakthroughs in the understanding of the role of melanocortins in human pigmentation and the DNA damage response of human melanocytes to solar ultraviolet radiation (UV). This began with the cloning of the melanocortin 1 receptor (MC1R) gene from human melanocytes and the demonstration that the encoded receptor is functional. Subsequently, population studies found that the MC1R gene is highly polymorphic, and that some of its variants are associated with red hair phenotype, fair skin and poor tanning ability. Using human melanocytes cultured from donors with different MC1R genotypes revealed that the alleles associated with red hair color encode for a non-functional receptor. Epidemiological studies linked the MC1R red hair color variants to increased melanoma risk. Investigating the impact of different MC1R variants on the response of human melanocytes to UV led to the important discovery that the MC1R signaling activates antioxidant, DNA repair and survival pathways, in addition to stimulation of eumelanin synthesis. These effects of MC1R were absent in melanocytes expressing 2 MC1R red hair color variants that result in loss of function of the receptor. The importance of the MC1R in reducing UV-induced genotoxicity in melanocytes led us to design small peptide analogs of the physiological MC1R agonist α-melanocortin (α-melanocyte stimulating hormone; α-MSH) for the goal of utilizing them for melanoma chemoprevention.

Neural melanocortin receptors in obesity and related metabolic disorders

Obesity is a global health issue, as it is associated with increased risk of developing chronic conditions associated with disorders of metabolism such as type 2 diabetes and cardiovascular disease. A better understanding of how excessive fat accumulation develops and causes diseases of the metabolic syndrome is urgently needed. The hypothalamic melanocortin system is an important point of convergence connecting signals of metabolic status with the neural circuitry that governs appetite and the autonomic and neuroendocrine system controling metabolism. This system has a critical role in the defense of body weight and maintenance of homeostasis. Two neural melanocortin receptors, melanocortin 3 and 4 receptors (MC3R and MC4R), play crucial roles in the regulation of energy balance. Mutations in the MC4R gene are the most common cause of monogenic obesity in humans, and a large literature indicates a role in regulating both energy intake through the control of satiety and energy expenditure. In contrast, MC3Rs have a more subtle role in energy homeostasis. Results from our lab indicate an important role for MC3Rs in synchronizing rhythms in foraging behavior with caloric cues and maintaining metabolic homeostasis during periods of nutrient scarcity. However, while deletion of the Mc3r gene in mice alters nutrient partitioning to favor accumulation of fat mass no obvious role for MC3R haploinsufficiency in human obesity has been reported. This article is part of a Special Issue entitled: Modulation of Adipose Tissue in Health and Disease.

The role of humans in facilitating and sustaining coat colour variation in domestic animals

Though the process of domestication results in a wide variety of novel phenotypic and behavioural traits, coat colour variation is one of the few characteristics that distinguishes all domestic animals from their wild progenitors. A number of recent reviews have discussed and synthesised the hundreds of genes known to underlie specific coat colour patterns in a wide range of domestic animals. This review expands upon those studies by asking how what is known about the causative mutations associated with variable coat colours, can be used to address three specific questions related to the appearance of non wild-type coat colours in domestic animals. Firstly, is it possible that coat colour variation resulted as a by-product of an initial selection for tameness during the early phases of domestication? Secondly, how soon after the process began did domestic animals display coat colour variation? Lastly, what evidence is there that intentional human selection, rather than drift, is primarily responsible for the wide range of modern coat colours? By considering the presence and absence of coat colour genes within the context of the different pathways animals travelled from wild to captive populations, we conclude that coat colour variability was probably not a pleiotropic effect of the selection for tameness, that coat colours most likely appeared very soon after the domestication process began, and that humans have been actively selecting for colour novelty and thus allowing for the proliferation of new mutations in coat colour genes.

Maternal exposure to bisphenol A and genistein has minimal effect on A(vy)/a offspring coat color but favors birth of agouti over nonagouti mice

Reports that maternal diet influences coat color in mouse offspring carrying the agouti A(vy) allele have received considerable attention because the range, from pseudoagouti (brown) to yellow, predicts adult health outcomes, especially disposition toward obesity and diabetes, in yellower mice. Bisphenol A (BPA), an endocrine-disrupting compound with estrogenic properties, fed to a/a dams harboring A(vy)/a conceptuses has been reported to induce a significant shift toward yellower mice, whereas consumption of either genistein (G) alone or in combination with BPA led to greater numbers of healthy, brown offspring. Groups of C57/B6 a/a females, which are nonagouti, were fed either a phytoestrogen-free control diet or one of six experimental diets: diets 1-3 contained BPA (50 mg, 5 mg, and 50 μg BPA/kg food, respectively); diet 4 contained G (250 mg/kg food); diet 5 contained G plus BPA (250 and 50 mg/kg food, respectively); and diet 6 contained 0.1 μg of ethinyl estradiol (EE)/kg food. Mice were bred to A(vy)/a males over multiple parities. In all, 2,824 pups from 426 litters were born. None of the diets provided any significant differences in relative numbers of brown, yellow, or intermediate coat color A(vy)/a offspring. However, BPA plus G (P < 0.0001) and EE diets (P = 0.005), but not the four others, decreased the percentage of black (a/a) to A(vy)/a offspring from the expected Mendelian ratio of 1:1. Data suggest that A(vy)/a conceptuses, which may possess a so-called "thrifty genotype," are at a competitive advantage over a/a conceptuses in certain uterine environments.

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.

Biology of obesity: lessons from animal models of obesity

Obesity is an epidemic problem in the world and is associated with several health problems, including diabetes, cardiovascular disease, respiratory failure, muscle weakness, and cancer. The precise molecular mechanisms by which obesity induces these health problems are not yet clear. To better understand the pathomechanisms of human disease, good animal models are essential. In this paper, we will analyze animal models of obesity and their use in the research of obesity-associated human health conditions and diseases such as diabetes, cancer, and obstructive sleep apnea syndrome.

Characterization of the rabbit agouti signaling protein (ASIP) gene: transcripts and phylogenetic analyses and identification of the causative mutation of the nonagouti black coat colour

The agouti locus encodes the agouti signalling protein (ASIP) which is involved in determining the switch from eumelanin to pheomelanin synthesis in melanocytes. In the domestic rabbit (Oryctolagus cuniculus) early studies indicated three alleles at this locus: A, light-bellied agouti (wild type); a(t), black and tan; a, black nonagouti. We characterized the rabbit ASIP gene and identified the causative mutation (an insertion in exon 2) of the black nonagouti allele whose frequency was evaluated in 31 breeds. Phylogenetic analysis of ASIP sequences from Oryctolagus and 9 other species of the family Leporidae placed Oryctolagus as sister species to Pentalagus and Bunolagus. Transcription analysis in wild type agouti rabbits revealed the presence of two major transcripts with different 5'-untranslated regions having ventral or dorsal skin specific expression. ASIP gene transcripts were also detected in all examined rabbit tissues distinguishing the rabbit expression pattern from what was observed in wild type mice.

A gene duplication affecting expression of the ovine ASIP gene is responsible for white and black sheep

Agouti signaling protein (ASIP) functions to regulate pigmentation in mice, while its role in many other animals and in humans has not been fully determined. In this study, we identify a 190-kb tandem duplication encompassing the ovine ASIP and AHCY coding regions and the ITCH promoter region as the genetic cause of white coat color of dominant white/tan (A(Wt)) agouti sheep. The duplication 5' breakpoint is located upstream of the ASIP coding sequence. Ubiquitous expression of a second copy of the ASIP coding sequence regulated by a duplicated copy of the nearby ITCH promoter causes the white sheep phenotype. A single copy ASIP gene with a silenced ASIP promoter occurs in recessive black sheep. In contrast, a single copy functional wild-type (A(+)) ASIP is responsible for the ancient Barbary sheep coat color phenotype. The gene duplication was facilitated by homologous recombination between two non-LTR SINE sequences flanking the duplicated segment. This is the first sheep trait attributable to gene duplication and shows nonallelic homologous recombination and gene conversion events at the ovine ASIP locus could have an important role in the evolution of sheep pigmentation.

Expression and localization of melanocortin-1 receptor in human adipose tissues of severely obese patients

OBJECTIVE

The melanocortin system is a key regulator in the hypothalamus of energy intake and expenditure. It is frequently linked with obesity and apparently modulates sympathetic outflow to white adipose tissues. The role of the melanocortins within adipose tissues, however, is not entirely clear. This study was aimed at determining the quantitative expression of the five melanocortin receptors (MC1-R to MC5-R) in subcutaneous and omental fat of obese patients and non-obese subjects.

RESEARCH METHODS AND PROCEDURES

Expression of MC1-R to MC5-R, proopiomelanocortin, agouti signaling protein, leptin, leptin receptor, and uncoupling protein-1 was investigated in human fat samples by quantitative reverse transcription-polymerase chain reaction. MC1-R expression was also studied in preadipocytes, adipocytes, and monocytic THP-1 cells and by immunohistochemical localization in adipose tissues.

RESULTS

Notable expression was found for MC1-R, whereas no mRNA for MC2-R and MC3-R was detected; MC4-R and MC5-R mRNA was occasionally detectable but at very low levels. MC1-R mRNA in subcutaneous fat was increased in obese patients as compared with controls; omental fat of both groups had slightly higher MC1-R expression than subcutaneous fat and did not differ between patient groups. Immunohistochemical analysis of the MC1-R in adipose tissue sections showed that MC1-R expression was higher in macrophages but also present in adipocytes.

DISCUSSION

The expression of MC1-R and the lack of MC2-R in human adipose tissues indicate that the melanocortins may regulate cell proliferation and/or inflammatory signals rather than lipolysis. Also, the increased expression of MC1-R in subcutaneous fat of obese subjects may reflect one aspect of the pathophysiology of obesity.

Investigation of the role of the agouti signaling protein gene (ASIP) in coat color evolution in primates

We investigated variation in the gene encoding the agouti signaling protein (ASIP) in relation to coat color evolution in primates. We found little evidence that mutations in the coding region of ASIP have been involved in color changes among closely related primate species. Among many closely related species with differing coat color, the coding region of ASIP was identical. In two cases (Sulawesi macaque and black lion tamarin) where species with almost completely black coat color had derived point mutations in exon 4 of the ASIP coding sequence, the same mutations did not alter coloration in other mammals and so probably do not affect ASIP function. Evolutionary reconstructions of two key phenotypes that are typically related to ASIP function--transverse phaeomelanin bands on hairs and pale ventral coloration--showed that these usually evolved concurrently, suggesting that loci acting downstream of ASIP may be involved. Analysis of dN/dS ratios revealed a likely change in functional constraint on ASIP following loss of agouti-banded hairs + pale ventral coloration, particularly in catarrhine primates (humans, apes, and Old World monkeys). Together with previous results on a lack of association of coat color with MC1R variation, these results suggest that other loci probably have an important role in primate coat color evolution.

Design, synthesis, and biological evaluation of a new class of small molecule peptide mimetics targeting the melanocortin receptors

A new bicyclic template has been developed for the synthesis of peptide mimetics. Straightforward synthetic steps, starting from amino acids, allow the facile construction of a wide range of analogs. This system was designed to target the melanocortin receptors (MCRs), with functional group selection based on a known pharmacophore and guidance from molecular modeling to rationally identify positional and stereochemical isomers likely to be active. The functions of hMCRs are critical to myriad biological activities, including pigmentation, steroidogenesis, energy homeostasis, erectile activity, and inflammation. These G-protein-coupled receptors (GPCRs) are targets for drug discovery in a number of areas, including cancer, pain, and obesity therapeutics. All compounds from this series tested to date are antagonists which bind with high affinity. Importantly, many are highly selective for a particular MCR subtype, including some of the first completely hMC5R-selective antagonists reported.

The insertion of a full-length Bos taurus LINE element is responsible for a transcriptional deregulation of the Normande Agouti gene

Mammalian pigmentation is controlled by the concerted action of Tyr, Tyrp1 and Dct producing eumelanin and/or pheomelanin in melanocytes. The ratio of these two pigments is determined by the agonist alpha-melanocyte stimulating hormone and the antagonist Agouti protein acting on the Mc1r. Here we show that the Agouti gene is over-expressed in Normande breed compared with Prim'Holstein breed. The Normande cattle have a characteristic coat color phenotype with a variable presence of black (eumelanin) hair over a red/brown background. We have found a previously undescribed full-length L1-BT element inserted in the 5'-genomic sequence of the Agouti gene in Normande cattle which promotes the over-expression of alternative transcripts. The variable expression of the alternative transcript directed by the long interspersed nuclear element promoter may be the origin of the brindle coat color pattern of the Normande breed. This new bovine Agouti allele isolated in Normande breed has been named Abr. Finally, as ectopic over-expression of Agouti in Ay mice is responsible for the obesity syndrome, we discuss the possible consequences of Abr for meat and milk production in cattle.

Alu-mediated 100-kb deletion in the primate genome: the loss of the agouti signaling protein gene in the lesser apes

Agouti signaling protein (ASIP) is an endogenous antagonist of melanocortin receptors that controls a wide range of physiological functions. Its central role in regulation of the melanocortin system implied that ASIP has been relevant to the evolution of various physiological traits in primates. In this study, we have tried to determine DNA sequences of the ASIP gene (ASIP) of various simian species to find molecular evolutionary aspects of ASIP. Unexpectedly, we found that the whole coding region of ASIP was missing only from the gibbon genome; gibbons constitute a large group of hominoid species in Southeast Asia. Our analyses revealed that unequal homologous recombination mediated by two AluSx elements erased a approximately 100-kb region including ASIP from the gibbon genome. The data provide new evidence for the significant roles of Alu elements in the dynamic evolution of the primate genome.

The mutation causing the black-and-tan pigmentation phenotype of Mangalitza pigs maps to the porcine ASIP locus but does not affect its coding sequence

The gene for agouti signaling protein (ASIP) is centrally involved in the expression of coat color traits in animals. The Mangalitza pig breed is characterized by a black-and-tan phenotype with black dorsal pigmentation and yellow or white ventral pigmentation. We investigated a Mangalitza x Piétrain cross and observed a coat color segregation pattern in the F2 generation that can be explained by virtue of two alleles at the MC1R locus and two alleles at the ASIP locus. Complete linkage of the black-and-tan phenotype to microsatellite alleles at the ASIP locus on SSC 17q21 was observed. Corroborated by the knowledge of similar mouse coat color mutants, it seems therefore conceivable that the black-and-tan pigmentation of Mangalitza pigs is caused by an ASIP allele a(t), which is recessive to the wild-type allele A. Toward positional cloning of the a(t) mutation, a 200-kb genomic BAC/PAC contig of this chromosomal region has been constructed and subsequently sequenced. Full-length ASIP cDNAs obtained by RACE differed in their 5' untranslated regions, whereas they shared a common open reading frame. Comparative sequencing of all ASIP exons and ASIP cDNAs between Mangalitza and Piétrain pigs did not reveal any differences associated with the coat color phenotype. Relative qRT-PCR analyses showed different dorsoventral skin expression intensities of the five ASIP transcripts in black-and-tan Mangalitza. The a(t) mutation is therefore probably a regulatory ASIP mutation that alters its dorsoventral expression pattern.

The Role of Dairy Foods in Weight Management

Dietary calcium appears to play a pivotal role in the regulation of energy metabolism and obesity risk. High calcium diets attenuate body fat accumulation and weight gain during periods of over-consumption of an energy-dense diet and to increase fat breakdown and preserve metabolism during caloric restriction, thereby markedly accelerating weight and fat loss. This effect is mediated primarily by circulating calcitriol, which regulates adipocyte intracellular Ca(2+). Studies of human adipocyte metabolism demonstrate a key role for intracellular Ca(2+) in regulating lipid metabolism and triglyceride storage, with increased intracellular Ca(2+) resulting in stimulation of lipogenic gene expression and lipogenesis and suppression of lipolysis, resulting in adipocyte lipid filling and increased adiposity. Moreover, the increased calcitriol produced in response to low calcium diets stimulates adipocyte Ca(2+) influx and, consequently, promotes adiposity, while higher calcium diets inhibit lipogenesis, promote lipolysis, lipid oxidation and thermogenesis and inhibit diet-induced obesity in mice. Notably, dairy sources of calcium exert markedly greater effects in attenuating weight and fat gain and accelerating fat loss. This augmented effect of dairy products versus supplemental calcium has been localized, in part, to the whey fraction of dairy and is likely due to additional bioactive compounds, such as angiotensin converting enzyme (ACE) inhibitors in dairy, as well as the rich concentration of branched chain amino acids, which act synergistically with calcium to attenuate adiposity; however, these compounds do not fully account for the observed effects, as whey has significantly greater bioactivity than found in these compounds. These concepts are confirmed by epidemiological data as well as recent clinical trials which demonstrate that diets which include at least three daily servings of dairy products result in significant reductions in body fat mass in obese humans in the absence of caloric restriction and markedly accelerates the weight and body fat loss secondary to caloric restriction compared to low dairy diets. These data indicate an important role for dairy products in both the ability to maintain a healthy weight and the management of overweight and obesity.

Gene polymorphisms and their effects in the melanocortin system

In addition to its role in human pigmentation, components of the melanocortin system regulate appetite, energy homeostasis and hormone production. Recent studies have suggested possible roles of this system in immunity, transmission of pain signals, and reproductive potential. A number of polymorphisms have been identified in genes of the melanocortin system and are associated with pigmentation in humans, as well as being causative of disorders of adrenal hormone production and obesity. This review gives an outline of these polymorphisms, their functional significance and possible application to or impact on diagnosis and pharmacotherapy based on melanocortin pathways.

Dose-response effects of ectopic agouti protein on iron overload and age-associated aspects of the Avy/a obese mouse phenome

Isogenic and congenic offspring from matings of inbred black a/a dams by sibling (or non-sibling from another inbred strain) yellow agouti Avy/a sires provide an animal model of obese yellow agouti Avy/a and isogenic lean pseudoagouti Avy/a mice exhibiting two different in vivo concentrations (high, very low) of ectopic agouti protein (ASP) with congenic lean black a/a mice as null controls. This makes it possible to differentiate between the high and very low dose levels of ectopic ASP with respect to interactions with diverse physiological and molecular pathways. Assay of differential responses to 12 or 24 months of carbonyl iron overload assessed the possible suitability of this animal model for the study of hemochromatosis. Agouti A/a B6C3F1 mice were used as non-congenic null controls. The age-related waxing and waning of body weight, food consumption, and caloric efficiency, as well as associated changes in pancreatic islets and islet cells, and formation of liver tumors were assayed. While the hypothesis that these mice might serve as a tool for investigating hemochromatosis was not confirmed, the data did provide evidence that even the very low levels of ASP in pseudoagouti Avy/a mice affect the network of molecular/metabolic/physiological response pathways that comprises the yellow agouti obese phenome. We suggest that the combination of yellow agouti Avy/a, pseudoagouti Avy/a, and black a/a congenic mice provides a practical tool for applying a dose-response systems biology approach to understanding the dysregulatory influence of ectopic ASP on the molecular-physiological matrix of the organism.

Sequence-specific cleavage of hepatitis X RNA in cis and trans by novel monotarget and multitarget hammerhead motif-containing ribozymes

We constructed two monoribozymes and a diribozyme against the conserved region of the X RNA of hepatitis B virus (HBV). All the ribozymes (Rzs) possessed sequence-specific cleavage activities under standard and simulated physiologic conditions. Specific cleavage was also obtained when the same Rzs were placed in cis configuration with respect to X gene in multiple combinations. Rz-expressing cells were able to specifically interfere with the functional expression of X RNA and protein production in a liver-specific cell line HepG2. Potential applications of these novel Rzs are discussed.

Widespread expression of the bovine Agouti gene results from at least three alternative promoters

In wild-type mice, it is well known that Agouti is only expressed in skin where it controls the banded-hair phenotype. As a first step to investigate the physiological role of Agouti in cattle, we isolated the corresponding gene and studied its expression pattern. We found no evidence of coding-region sequence variation within and between eight breeds representing a large panel of coat colour phenotypes. We detected by northern hybridization two Agouti mRNA isoforms in brain, heart, lung, liver, kidney, spleen and a third in skin. We characterized the full-length Agouti transcript in skin and isolated the 5'UTR of two mRNAs expressed in the other tissues. The three mRNAs have the same coding region but differ by their 5' untranslated regions. Upstream regulatory sequences display two alternative promoters involved with the broad expression in tissues other than skin. Interestingly, these sequences are highly homologous to upstream sequences of the orthologous human (76-85% identity) and pig (82-86% identity) ASIP genes. In addition to its potential role in pigmentation (as seen in mice), we suggest that bovine Agouti could be involved in various physiological functions. Furthermore, the significant homology between cattle, pig and human regulatory sequences indicate that these orthologous genes are regulated alike. Lastly, since the 5'UTR of many eukaryotic mRNAs are physiologically relevant, their impact on bovine Agouti mRNA performance is discussed.

Melanin pigmentation in mammalian skin and its hormonal regulation

Cutaneous melanin pigment plays a critical role in camouflage, mimicry, social communication, and protection against harmful effects of solar radiation. Melanogenesis is under complex regulatory control by multiple agents interacting via pathways activated by receptor-dependent and -independent mechanisms, in hormonal, auto-, para-, or intracrine fashion. Because of the multidirectional nature and heterogeneous character of the melanogenesis modifying agents, its controlling factors are not organized into simple linear sequences, but they interphase instead in a multidimensional network, with extensive functional overlapping with connections arranged both in series and in parallel. The most important positive regulator of melanogenesis is the MC1 receptor with its ligands melanocortins and ACTH, whereas among the negative regulators agouti protein stands out, determining intensity of melanogenesis and also the type of melanin synthesized. Within the context of the skin as a stress organ, melanogenic activity serves as a unique molecular sensor and transducer of noxious signals and as regulator of local homeostasis. In keeping with these multiple roles, melanogenesis is controlled by a highly structured system, active since early embryogenesis and capable of superselective functional regulation that may reach down to the cellular level represented by single melanocytes. Indeed, the significance of melanogenesis extends beyond the mere assignment of a color trait.

Mouse models of obesity

Insights into the etiology of human obesity have arisen from the study of animal models. Animal models of obesity are also important for the development of future treatments of obesity. An agouti mouse mutation resulting in obese, yellow mice was described over a century ago and in 1992 agouti was cloned, making it the first obesity gene characterized at the molecular level. The lethal yellow mouse mutation is one of five dominant agouti mutations and is an excellent model for human obesity. The molecular categorization of agouti was responsible for the elucidation of the melanocortin system's involvement in hypothalamic weight regulation. As genetic knowledge increases many transgenic mice have been created with genes either over-expressed or deleted, models which further enhance the understanding of obesity.

Population Differences in the Frequency of the Agouti Signaling Protein g.8818A>G Polymorphism

The role of agouti signaling protein (ASIP) in human pigmentation pathways is not definitively understood although its murine homologue regulates, in part, pheomelanogenesis. We have reported an association of a polymorphism in the 3'-untranslated region of ASIP (g.8818A>G) with dark hair and eye color among a group of European-Americans (Am J Hum Genet 2002 March;70:770). Among 147 healthy control subjects, the frequency of the G-allele was 0.12. We hypothesized that this polymorphism would occur at different frequencies among different population groups. Using PCR-RFLP, we genotyped 25 East Asian, 86 African-American, and 207 West African individuals for the ASIP g.8818A>G polymorphism. The g.8818G-allele was present in the West African sample at a frequency of 0.80, in the African-American sample at a frequency of 0.62, and in the East Asian sample at 0.28. The difference in allele frequency among population groups was statistically significant (P < 0.0001). Although the effect of the g.8818A>G polymorphism upon ASIP function is unknown, the large difference in allele frequency between our West African and European-American sample populations lends support to the notion that this gene may be important in human pigmentation.

The human RAP250 gene: genomic structure and promoter analysis

Ligand-induced gene activation by nuclear receptors involves the recruitment of coactivators to hormone bound receptors. Recent results have shown that RAP250, also termed as ASC-2/PRIP/TRBP/NRC/AIB3, plays a critical role as a coactivator of nuclear receptors. In this study, we have determined the genomic organization of the human RAP250 gene in order to identify the promoter region. By searching the GenBank database for EST sequences, we could identify two previously unknown exons in the 5'-end of the gene. Our results show that the RAP250 gene consists of 15 exons spanning 111 kb. All sequences of the splice donor and acceptor sites fit the GT-AG role for splicing. We also show using linkage analysis that the mouse Rap250 gene is located on chromosome 2 close to the agouti gene. The RAP250 promoter is GC-rich and TATA-less, and contains multiple Sp1 binding sites and a MYC binding site. A reporter plasmid containing the 5' flanking region of the RAP250 gene showed significant activity compared to pGL3-basic and minimal thymidine kinase (TK) reporter plasmids in transfection experiments using luciferase reporter genes. Our data show that the RAP250 has a complex genomic structure with a promoter that is regulated by multiple transcription factors for its basal expression.

Sequences Associated With Human Iris Pigmentation

To determine whether and how common polymorphisms are associated with natural distributions of iris colors, we surveyed 851 individuals of mainly European descent at 335 SNP loci in 13 pigmentation genes and 419 other SNPs distributed throughout the genome and known or thought to be informative for certain elements of population structure. We identified numerous SNPs, haplotypes, and diplotypes (diploid pairs of haplotypes) within the OCA2, MYO5A, TYRP1, AIM, DCT, and TYR genes and the CYP1A2-15q22-ter, CYP1B1-2p21, CYP2C8-10q23, CYP2C9-10q24, and MAOA-Xp11.4 regions as significantly associated with iris colors. Half of the associated SNPs were located on chromosome 15, which corresponds with results that others have previously obtained from linkage analysis. We identified 5 additional genes (ASIP, MC1R, POMC, and SILV) and one additional region (GSTT2-22q11.23) with haplotype and/or diplotypes, but not individual SNP alleles associated with iris colors. For most of the genes, multilocus gene-wise genotype sequences were more strongly associated with iris colors than were haplotypes or SNP alleles. Diplotypes for these genes explain 15% of iris color variation. Apart from representing the first comprehensive candidate gene study for variable iris pigmentation and constituting a first step toward developing a classification model for the inference of iris color from DNA, our results suggest that cryptic population structure might serve as a leverage tool for complex trait gene mapping if genomes are screened with the appropriate ancestry informative markers.

Agouti expression in human adipose tissue: functional consequences and increased expression in type 2 diabetes

It is well recognized that the agouti/melanocortin system is an important regulator of body weight homeostasis. Given that agouti is expressed in human adipose tissue and that the ectopic expression of agouti in adipose tissue results in moderately obese mice, the link between agouti expression in human adipose tissue and obesity/type 2 diabetes was investigated. Although there was no apparent relationship between agouti mRNA levels and BMI, agouti mRNA levels were significantly elevated in subjects with type 2 diabetes. The regulation of agouti in cultured human adipocytes revealed that insulin did not regulate agouti mRNA, whereas dexamethasone treatment potently increased the levels of agouti mRNA. Experiments with cultured human preadipocytes and with cells obtained from transgenic mice that overexpress agouti demonstrated that melanocortin receptor (MCR) signaling in adipose tissue can regulate both preadipocyte proliferation and differentiation. Taken together, these results reveal that agouti can regulate adipogenesis at several levels and suggest that there are functional consequences of elevated agouti levels in human adipose tissue. The influence of MCR signaling on adipogenesis combined with the well-established role of MCR signaling in the hypothalamus suggest that adipogenesis is coordinately regulated with food intake and energy expenditure.

Regulation of PPARgamma and obesity by agouti/melanocortin signaling in adipocytes

To study the potential biological role of agouti/melanocortin signaling in human adipose tissue, we engineered transgenic mice to overexpress agouti in adipose tissue. The aP2-agouti transgenic mice become significantly heavier than littermates. The increased body weight is maintained at approximately 15% above nontransgenic mice through 20 weeks and is caused by increased fat mass. The obesity is increased by a high-fat diet. There is no change in food intake in the aP2-agouti mice suggesting changes in energy utilization. A possible mechanism is that the agouti/melanocortin signaling regulates levels of PPARgamma. PPARgamma functions as a major regulator of adipocyte differentiation and as a receptor for the antidiabetic thiazolidinediones. Agouti increases PPARgamma protein levels in differentiated 3T3-L1 adipocytes, and PPARgamma expression is elevated in the fat pads of the aP2-agouti transgenic mice. The modest weight gain observed in the transgenic mice suggests that hypothalamic pathways regulating food intake are intact and the observed adiposity is within ranges that can be achieved by a paracrine mechanism at the adipocyte level.

Role of dietary calcium and dairy products in modulating adiposity

Dietary calcium plays a pivotal role in the regulation of energy metabolism. High-calcium diets attenuate adipocyte lipid accretion and weight gain during overconsumption of an energy-dense diet and increase lipolysis and preserve thermogenesis during caloric restriction, thereby markedly accelerating weight loss. Our studies of the agouti gene demonstrate a key role for intracellular Ca2+ in regulating adipocyte lipid metabolism and TG storage. Increased intracellular Ca2+ resulting in stimulation of lipogenic gene expression, and lipogenesis and suppression of lipolysis resulting in adipocyte lipid filling and increased adiposity. Moreover, we recently demonstrated that the increased calcitriol produced in response to low-calcium diets stimulates adipocyte Ca2+ influx and, consequently, promotes adiposity. Accordingly, suppressing calcitriol levels by increasing dietary calcium is an attractive target for obesity intervention. In support of this concept, transgenic mice expressing the agouti gene specifically in adipocytes (a human-like pattern) respond to low-calcium diets with accelerated weight gain and fat accretion, whereas high-calcium diets markedly inhibit lipogenesis, accelerate lipolysis, increase thermogenesis, and suppress fat accretion and weight gain in animals maintained at identical caloric intakes. Further, low-calcium diets impede body fat loss, whereas high-calcium diets markedly accelerate fat loss in transgenic mice subjected to caloric restriction. Dairy sources of calcium exert markedly greater effects in attenuating weight and fat gain and accelerating fat loss. This augmented effect of dairy products is likely due to additional bioactive compounds in dairy that act synergistically with calcium to attenuate adiposity. These concepts are confirmed by both epidemiological and clinical data, which demonstrate that increasing dietary calcium results in significant reductions in adipose tissue mass in obese humans in the absence of caloric restriction and markedly accelerates the weight and body fat loss secondary to caloric restriction, whereas dairy products exert significantly greater effects. These data indicate an important role for dairy products in both the prevention and treatment of obesity.

Calcium intake and adiposity

Limited epidemiologic and experimental data support the possibility that dietary calcium intake plays a role in human body weight regulation. The aim of this review was to present the data from human studies that link calcium and dairy intake to body weight, describe the existing evidence for an effect of calcium intake on body weight from animal models of obesity, present evidence of a role for intracellular calcium in the regulation of lipogenesis and lipolysis, elucidate the potential suggested relation between dietary calcium intake and intracellular calcium concentrations, and outline the effects of calcium supplementation on dietary fat absorption. We suggest that these data support the need for large, population based clinical trials to assess the effects of supplemental calcium and other components of dairy products on human body weight.

Agouti signal protein regulation in human melanoma cells

Production of the pigment eumelanin is controlled by alpha-melanocyte stimulating hormone (alpha-MSH) stimulation of melanocortin 1 receptor (Mc1r), whereas production of pheomelanin results from agouti antagonism of alpha-MSH signalling through Mc1r. The role of agouti in mouse pigmentation has been extensively investigated but a role for agouti signalling protein (ASIP) in human pigmentation has not been determined. To determine whether ASIP regulates known melanogenic genes in humans, ASIP was over-expressed in a human melanoma cell line. Levels of mRNA and protein were measured in genes known to be up or down-regulated by agouti in the mouse, namely microphthalmia (Mitf), tyrosinase (Tyr), tyrosinase-related protein 1 (Tyrp1), dopachrome tautomerase (Dct), Mc1r, silver, initiation transcription factor 2 (Itf2) and mini chromosome maintenance protein 6 (Mcm6). These melanogenic genes were not found to be significantly up or down-regulated by ASIP at the transcriptional level in human melanoma cells. However, ASIP down-regulation of tyrp1 was observed at the translational level. To identify novel genes that may be regulated by ASIP in melanoma cells, microarrays were used to determine differences in gene expression between the control and ASIP transfected melanoma cells. The expression level of human RNAs were determined by microarray analysis using a 19,200 cDNA and a 19,200 oligonucleotide array representing 13,000 and 18,864 individual genes, respectively. Genes observed to be modulated by ASIP were confirmed by quantitative real-time polymerase chain reaction. Results identify five genes, namely PPARbeta, eIF-4B, RRM2, MINOR and EVI2B that are down-regulated by ASIP, indicating a likely role for ASIP in human melanogenesis.

Mechanisms of dairy modulation of adiposity

Dietary calcium plays a pivotal role in the regulation of energy metabolism, in that we have found high calcium diets to attenuate adipocyte lipid accretion and weight gain during periods of overconsumption of an energy-dense diet and to increase lipolysis and preserve thermogenesis during caloric restriction, thereby markedly accelerating weight loss. Our studies of the agouti gene in obesity and insulin resistance demonstrate a key role for intracellular Ca(2+) in regulating adipocyte lipid metabolism and triglyceride storage, with increased intracellular Ca(2+), resulting in stimulation of lipogenic gene expression and lipogenesis, and suppression of lipolysis, resulting in adipocyte lipid filling and increased adiposity. Moreover, we have recently demonstrated that the increased calcitriol produced in response to low calcium diets stimulates Ca(2+) influx in human adipocytes and thereby promotes adiposity. Accordingly, suppressing calcitriol levels by increasing dietary calcium is an attractive target for the prevention and management of obesity. In support of this concept, transgenic mice expressing the agouti gene specifically in adipocytes (a humanlike pattern) respond to low calcium diets with accelerated weight gain and fat accretion, whereas high calcium diets markedly inhibit lipogenesis, accelerate lipolysis, increase thermogenesis and suppress fat accretion and weight gain in animals maintained at identical caloric intakes. Further, low calcium diets impede body fat loss, whereas high calcium diets markedly accelerate fat loss in transgenic mice subjected to caloric restriction. Notably, dairy sources of calcium exert markedly greater effects in attenuating weight and fat gain and accelerating fat loss. This augmented effect of dairy vs. supplemental calcium is likely attributable to additional bioactive compounds in dairy that act synergistically with calcium to attenuate adiposity; among these are angiotensin converting enzyme inhibitory peptides, which limit angiotensin II production and thereby limit angiotensin II stimulation of adipocyte lipogenesis. These concepts are confirmed by both epidemiological and clinical data, which similarly demonstrate that dairy products exert a substantially greater effect on both fat loss and fat distribution compared to an equivalent amount of supplemental calcium.

Body mass index-related human adipocyte agouti expression is sex-specific but not depot-specific

OBJECTIVE

To determine if human adipocyte agouti signal protein (ASIP) mRNA expression is associated with obesity and is gender and/or depot specific.

RESEARCH METHODS AND PROCEDURES

Subjects included 8 men (64 +/- 3 years) and 14 women (56 +/- 15 years) undergoing elective abdominal surgery. ASIP mRNA levels in isolated omental and subcutaneous abdominal adipocytes were measured by quantitative reverse transcription polymerase chain reaction.

RESULTS

No significant depot difference was observed between genders; ASIP mRNA levels of omental and subcutaneous abdominal adipocytes were pooled for this analysis. BMI and ASIP gene expression were negatively correlated in men (rho = -0.70; p < 0.05), whereas a positive relationship was observed in women (rho = 0.48; p < 0.05). No significant difference was observed in age, body weight, body mass index (BMI), and waist circumference between groups. Hip circumference was significantly higher in women than in men (p < 0.05). Also, no significant difference in ASIP mRNA expression was observed between men and women, regardless of the fat depot.

DISCUSSION

These results show that men and women of similar age and BMI present similar ASIP mRNA levels in omental and subcutaneous abdominal adipocytes. However, a sexual dimorphism exists in the relationship between ASIP expression and BMI. If ASIP is involved in appetite regulation or energy homeostasis in humans, this observation may contribute to the recognized differences in these parameters between men and women.

A polymorphism in the agouti signaling protein gene is associated with human pigmentation

In mice and humans, binding of alpha-melanocyte--stimulating hormone to the melanocyte-stimulating--hormone receptor (MSHR), the protein product of melanocortin-1 receptor (MC1R) gene, leads to the synthesis of eumelanin. In the mouse, ligation of MSHR by agouti signaling protein (ASP) results in the production of pheomelanin. The role of ASP in humans is unclear. We sought to characterize the agouti signaling protein gene (ASIP) in a group of white subjects, to assess whether ASIP was a determinant of human pigmentation and whether this gene may be associated with increased melanoma risk. We found no evidence of coding-region sequence variation in ASIP, but detected a g.8818A-->G polymorphism in the 3' untranslated region. We genotyped 746 participants in a study of melanoma susceptibility for g.8818A-->G, by means of polymerase chain reaction and restriction fragment--length polymorphism analysis. Among the 147 healthy controls, the frequency of the G allele was.12. Carriage of the G allele was significantly associated with dark hair (odds ratio 1.8; 95% confidence interval [CI] 1.2--2.8) and brown eyes (odds ratio 1.9; 95% CI 1.3--2.8) after adjusting for age, gender, and disease status. ASIP g.8818A-->G was not associated independently with disease status. This is the first report of an association of ASIP with specific human pigmentation characteristics. It remains to be investigated whether the interaction of MC1R and ASIP can enhance prediction of human pigmentation and melanoma risk.

Agouti: from mouse to man, from skin to fat

The agouti protein regulates pigmentation in the mouse hair follicle producing a black hair with a subapical yellow band. Its effect on pigmentation is achieved by antagonizing the binding of alpha-melanocyte stimulating hormone (alpha-MSH) to melanocortin 1 receptor (Mc1r), switching melanin synthesis from eumelanin (black/brown) to phaeomelanin (red/yellow). Dominant mutations in the non-coding region of mouse agouti cause yellow coat colour and ectopic expression also results in obesity, type 11 diabetes, increased somatic growth and tumourigenesis. At least some of these pleiotropic effects can be explained by antagonism of other members of the melanocortin receptor family by agouti protein. The yellow coat colour is the result of agouti chronically antagonizing the binding of alpha-MSH to Mc1r and the obese phenotype results from agouti protein antagonizing the binding of alpha-MSH to Mc3r and/or Mc4r. Despite the existence of a highly homologous agouti protein in humans, agouti signal protein (ASIP), its role has yet to be defined. However it is known that human ASIP is expressed at highest levels in adipose tissue where it may antagonize one of the melanocortin receptors. The conserved nature of the agouti protein combined with the diverse phenotypic effects of agouti mutations in mouse and the different expression patterns of human and mouse agouti, suggest ASIP may play a role in human energy homeostasis and possibly human pigmentation.

Molecular and phenotypic analysis of 25 recessive, homozygous-viable alleles at the mouse agouti locus

Agouti is a paracrine-acting, transient antagonist of melanocortin 1 receptors that specifies the subapical band of yellow on otherwise black hairs of the wild-type coat. To better understand both agouti structure/function and the germline damage caused by chemicals and radiation, an allelic series of 25 recessive, homozygous-viable agouti mutations generated in specific-locus tests were characterized. Visual inspection of fur, augmented by quantifiable chemical analysis of hair melanins, suggested four phenotypic categories (mild, moderate, umbrous-like, severe) for the 18 hypomorphs and a single category for the 7 amorphs (null). Molecular analysis indicated protein-coding alterations in 8 hypomorphs and 6 amorphs, with mild-moderate phenotypes correlating with signal peptide or basic domain mutations, and more devastating phenotypes resulting from C-terminal lesions. Ten hypomorphs and one null demonstrated wild-type coding potential, suggesting that they contain mutations elsewhere in the > or = 125-kb agouti locus that either reduce the level or alter the temporal/spatial distribution of agouti transcripts. Beyond the notable contributions to the field of mouse germ cell mutagenesis, analysis of this allelic series illustrates that complete abrogation of agouti function in vivo occurs most often through protein-coding lesions, whereas partial loss of function occurs slightly more frequently at the level of gene expression control.