Sequence interpretation. Functional annotation of mouse genome sequences.
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Animals↗
Biomedical subjects
G Barsh
Publications and source records attributed to G Barsh.
Functional annotation of a full-length mouse cDNA collection.
The RIKEN Mouse Gene Encyclopaedia Project, a systematic approach to determining the full coding potential of the mouse genome, involves collection and sequencing of full-length complementary DNAs and physical mapping of the corresponding genes to the mouse genome. We organized an international functional annotation meeting (FANTOM) to annotate the first 21,076 cDNAs to be analysed in this project. Here we describe the first RIKEN clone collection, which is one of the largest described for any organism. Analysis of these cDNAs extends known gene families and identifies new ones.
Animals↗
Biochemical and genetic studies of pigment-type switching.
Mutations that affect the balance between the synthesis of eumelanin and pheomelanin provide a powerful set of tools with which to understand general aspects of cell signaling. Previous work from our laboratory has demonstrated that pheomelanin synthesis is triggered by the ability of Agouti protein to inhibit signaling through the Melanocortin 1 receptor (Mc1r). In a bioassay based on the Xenopus Mc1r, Agouti protein has two effects, competitive inhibition of receptor occupancy by alpha-MSH and down-regulation of receptor signaling, which are mediated separately by domains in the amino- and carboxy-terminal regions of Agouti protein, respectively. Recently, we have used the genetics of pigmentation as an in vivo system to screen for and analyze other mutations in the Agouti-melanocortin pathway. The pigmentary effects of Agouti are suppressed by the previously existing coat-color mutations mahogany (mg), mahoganoid (md), and Umbrous (U). Double mutant studies, with animals deficient for the Mc1r or those which carry Ay, indicate that mg and md are genetically upstream of the Mc1r, and can suppress the effects of Ay on both pigmentation and body weight. Positional cloning has recently identified the gene mutated in mahogany as a single transmembrane-spanning protein whose ectodomain is orthologous to human Attractin (Atrn).
Agouti Signaling Protein↗
The melanocortin-1 receptor is a key regulator of human cutaneous pigmentation.
The cloning and characterization of the human melanocortin-1 receptor (MC1R) and the demonstration that normal human melanocytes respond to the melanocortins, alpha-melanocyte stimulating hormone (alpha-MSH) and adrenocorticotrophic hormone (ACTH), with increased proliferation and eumelanogenesis had put an end to a long-standing controversy about the role of melanocortins in regulating human cutaneous pigmentation. We have shown that alpha-MSH and ACTH bind the human MC1R with equal affinity, and are equipotent in their mitogenic and melanogenic effects on human melanocytes. We also showed that the activation of the MC1R is important for the melanogenic response of human melanocytes to ultraviolet radiation (UVR). The MC1R is also the principal mediator of the inhibitory effects of agouti signaling protein (ASP) on melanogenesis. Expression of the MC1R is subject to regulation by its own ligands alpha-MSH and ACTH, as well as by UVR and endothelin-1. Recent studies that we conducted on the expression of MC1R variants by human melanocytes and the implications of these variants on the function of the MC1R revealed the following. Human melanocytes homozygous for Arg160Trp mutation in the MC1R demonstrated a significantly reduced response to alpha-MSH. Also, this culture responded poorly to ASP and exhibited an exaggerated cytotoxic response to UVR. Another culture, which was homozygous for Val92Met mutation in the MC1R, demonstrated a normal response to alpha-MSH. Heterozygous mutations that are frequently expressed in various melanocyte cultures did not disrupt MC1R function. These results begin to elucidate the significance of MC1R variants in the function of the receptor. Our data emphasize the significance of a normally functioning MC1R in the response of melanocytes to melanocortins, ASP, and UVR.
Agouti Signaling Protein↗
Agouti-related protein-like immunoreactivity: characterization of release from hypothalamic tissue and presence in serum.
A novel RIA was used to examine the release of agouti-related protein-like immunoreactivity (AGRP-LI) from perfused rat hypothalamic tissue slices and to characterize AGRP-LI in rat serum. A continuous low level basal AGRP-LI release was observed from hypothalami of rats fed ad libitum before the rats were killed. Basal AGRP-LI release was 3-fold greater in rats fasted 48 h. In fasted animals leptin dose-dependently suppressed basal AGRP-LI release. In fed animals no change in basal AGRP-LI release was detected in response to 10(-6) M alpha-MSH, orexin B, melanin-concentrating hormone, or serotonin. HPLC analysis of AGRP-LI in rat serum identified a single peak that eluted in close proximity to synthetic AGRP (87-132) and mouse [Leu127Pro]AGRP and that was identical to the peak seen in hypothalamic and adrenal tissue extracts. The serum concentration of AGRP-LI in rats fed ad libitum was 0.865+/-0.323 nmol/liter (mean +/- SE). Food deprivation resulted in a slow, but statistically significant rise in serum immunoreactivity at 48 h [1.174+/-0.118 nmol/liter (mean +/- SE)]. Bilateral adrenalectomy did not change serum levels of AGRP-LI. These studies demonstrate that in the rat there are different levels of basal hypothalamic AGRP-LI release in fed and fasted states and that in the fasted rat this release can be profoundly suppressed by leptin. These studies also suggest that AGRP is present in the systemic circulation of rats.
Adrenal Glands↗
Neuroendocrine regulation by the Agouti/Agrp-melanocortin system.
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Agouti Signaling Protein↗
Of ancient tales and hairless tails.
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Animals↗
From Agouti to Pomc--100 years of fat blonde mice.
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Agouti Signaling Protein↗
Participation of the melanocortin-1 receptor in the UV control of pigmentation.
The cloning of the melanocortin-1 receptor (MC1R) gene from human melanocytes and the demonstration that these cells respond to the melanocortins alpha-melanocyte stimulating hormone (alpha-MSH) and adrenocorticotropic hormone (ACTH) with increased proliferation and melanogenesis have renewed the interest in investigation the physiological role of these hormones in regulating human pigmentation. Alpha-melanocyte stimulating hormone and ACTH are both synthesized in the human epidermis, and their synthesis is upregulated by exposure to ultraviolet radiation (UVR). Activation of the MC1R by ligand binding results in stimulation of cAMP formation, which is a principal mechanism for inducing melanogenesis. The increase in cAMP is required for the pigmentary response of human melanocytes to UVR, and for allowing them to overcome the UVR-induced G1 arrest. Treatment of human melanocytes with alpha-MSH increases eumelanin synthesis, an effect that is expected to enhance photoprotection of the skin. Population studies have revealed more than 20 allelic variants of the MC1R gene. Some of these variants are overexpressed in individuals with skin type I or II, red hair, and poor tanning ability. Future studies will aim at further exploration of the role of these variants in MC1R function, and in determining constitutive human pigmentation, the response to sun exposure, and possibly the susceptibility to skin cancer.
Alleles↗
Conserved and distinct roles of kreisler in regulation of the paralogous Hoxa3 and Hoxb3 genes.
During anteroposterior patterning of the developing hindbrain, the anterior expression of 3' Hox genes maps to distinct rhombomeric boundaries and, in many cases, is upregulated in specific segments. Paralogous genes frequently have similar anterior boundaries of expression but it is not known if these are controlled by common mechanisms. The expression of the paralogous Hoxa3 and Hoxb3 genes extends from the posterior spinal cord up to the rhombomere (r) 4/5 boundary and both genes are upregulated specifically in r5. However, in this study, we have found that Hoxa3 expression is also upregulated in r6, showing that there are differences in segmental expression between paralogues. We have used transgenic analysis to investigate the mechanisms underlying the pattern of segmental expression of Hoxa3. We found that the intergenic region between Hoxa3 and Hoxa4 contains several enhancers, which summed together mediate a pattern of expression closely resembling that of the endogenous Hoxa3 gene. One enhancer specifically directs expression in r5 and r6, in a manner that reflects the upregulation of the endogenous gene in these segments. Deletion analysis localized this activity to a 600 bp fragment that was found to contain a single high-affinity binding site for the Maf bZIP protein Krml1, encoded by the kreisler gene. This site is necessary for enhancer activity and when multimerized it is sufficient to direct a kreisler-like pattern in transgenic embryos. Furthermore the r5/r6 enhancer activity is dependent upon endogenous kreisler and is activated by ectopic kreisler expression. This demonstrates that Hoxa3, along with its paralog Hoxb3, is a direct target of kreisler in the mouse hindbrain. Comparisons between the Krml1-binding sites in the Hoxa3 and Hoxb3 enhancers reveal that there are differences in both the number of binding sites and way that kreisler activity is integrated and restricted by these two control regions. Analysis of the individual sites revealed that they have different requirements for mediating r5/r6 and dorsal roof plate expression. Therefore, the restriction of Hoxb3 to r5 and Hoxa3 to r5 and r6, together with expression patterns of Hoxb3 in other vertebrate species suggests that these regulatory elements have a common origin but have later diverged during vertebrate evolution.
Amino Acid Sequence↗
Subtype-specific differences in the intracellular sorting of G protein-coupled receptors.
We have examined the subcellular distribution of three subtypes of adrenergic receptor by immunocytochemical localization of wild-type and epitope-tagged proteins expressed in Cos-7 and K293 cells. Two subtypes (beta 2 and M alpha 2-10H) are localized in the plasma membrane at steady state in untreated cells, while another subtype (M alpha 2-4H) is found both in the plasma membrane and in a population of intracellular vesicles. Within 15 min following the addition of adrenergic agonists, beta 2 and M alpha 2-10H receptors are differentially sorted; beta 2 receptors are selectively internalized to intracellular vesicles, which are distinct from those containing M alpha 2-4H receptors, while M alpha 2-10H receptors remain in the plasma membrane. Subtype-specific sorting suggests a new class of functional properties that may differentiate the signaling and regulation of homologous G protein-coupled receptors.
Amino Acid Sequence↗
Cloning of two mouse genes encoding alpha 2-adrenergic receptor subtypes and identification of a single amino acid in the mouse alpha 2-C10 homolog responsible for an interspecies variation in antagonist binding.
Molecular cloning and ligand binding studies have shown the alpha 2 class of adrenergic receptor (alpha 2-AR) to be a family of at least three related subtypes in humans. These studies have not, however, identified distinct subtype-specific functions for these receptors in vivo. It should be possible to extend the analysis of alpha 2-AR subtype function to the animal level through the use of experimental mammalian embryology in mice. To begin this process, we have isolated two mouse genomic clones encoding alpha 2-AR subtypes and expressed these genes in COS-7 cells for binding studies. Sequence homology and ligand binding data allow the assignment of one clone (M alpha 2-4H) as the mouse homolog of the human alpha 2-C4 subtype. The other clone (M alpha 2-10H) closely resembles the human alpha 2-C10 subtype in sequence but binds with significantly lower affinity to yohimbine and rauwolscine, members of a distinct class of bulky alpha 2-selective antagonists commonly used to evaluate alpha 2-AR function in vivo. To define the domain(s) responsible for this unusual binding property, we constructed a series of M alpha 2-10H/human alpha 2-C10 chimeric receptors. Analysis of these receptors identified a conservative Cys201 to Ser201 change in the fifth transmembrane domain of M alpha 2-10H as being responsible for the low affinity of the mouse receptor for yohimbine.
Adrenergic alpha-Antagonists↗
Sialic acid metabolism in sialuria fibroblasts.
Sialuria is a rare inborn error of metabolism caused by excessive synthesis of sialic acid (N-acetylneuraminic acid, NeuAc). Fibroblasts cultured from the three known cases of sialuria contained 70-200-fold increases in soluble sialic acid, but normal concentrations of bound sialic acid. The sialic acid appeared in the cytosolic fraction of the cells on differential centrifugation, and was susceptible to borohydride reduction, suggesting that accumulated sialic acid was in the form of NeuAc and not CMP-NeuAc. In biochemical studies, CMP-NeuAc (50 microM) inhibited the UDP-N-acetylglucosamine (UDP-GlcNAc) 2-epimerase of normal fibroblasts by 84-100%, but inhibited the epimerase from sialuria cells by only 19-31%. Feeding sialuria cells up to 5 mM D-glucosamine for 72 h increased free sialic acid content 20-60%, but normal cells were unaffected by this treatment. Cytidine feeding (5 mM, 72 h) reduced the NeuAc content of sialuria cells, initially 112, 104, and 266 nmol/mg protein, by 63-71 nmol/mg protein; CMP-NeuAc concentrations, initially 4, 2, and 5 nmol/mg protein, increased by 14-33 nmol/mg protein. Consequently, the total cellular content of soluble sialic acid (NeuAc + CMP-NeuAc) was lowered 14-46% by cytidine feeding. The inheritance pattern of sialuria has not been determined. However, cells from both parents of one sialuria patient contained normal concentrations of free sialic acid, and the parental epimerase activity also responded normally to CMP-NeuAc. We conclude that the basic biochemical defect in all known cases of sialuria is a failure of CMP-NeuAc to feedback-inhibit UDP-GlcNAc 2-epimerase and cytidine feeding can lower the intracellular soluble sialic acid concentration of sialuria cells.
Child, Preschool↗
Pyridoxine-unresponsive homocystinuria with an unusual clinical course.
Progressive premature atherosclerosis and associated thromboembolic complications are the main causes of morbidity and mortality in patients with homocystinuria. However, thrombosis is rarely the predominant or presenting manifestation leading to the diagnosis of homocystinuria. We report on an otherwise asymptomatic teenage boy of normal intelligence who had a superior sagittal sinus thrombosis documented by CT and MRI scans. He presented with pneumothoraces, papilledema, and transient right hemiparesis. He subsequently developed empyema and necrotizing pneumonia as well as deep venous thromboses. The diagnosis of pyridoxine-unresponsive homocystinuria was made on the basis of clinical chemistry analyses, enzyme assay, and clinical trial. He has remained symptom-free under treatment with betaine and methionine restriction. We suggest that there exists a subset of patients with pyridoxine-unresponsive homocystinuria who are at risk for thromboembolism, but who may remain undiagnosed because of an otherwise mild clinical course.
Adolescent↗
Physical linkage of the genes for platelet membrane glycoproteins IIb and IIIa.
The fibrinogen receptor on human platelets is a prototypic member of the integrin family and is composed of subunit glycoproteins IIb (gpIIb) and IIIa (gpIIIa) in a 1:1 stoichiometric ratio. We have isolated cDNA clones for gpIIb and gpIIIa and localized both genes to chromosome 17. In the current study, several approaches were used to localize and map the genes for gpIIb and gpIIIa. A preliminary evaluation of subchromosomal localization was performed by using a panel of mouse-human somatic cell hybrids that contain different amounts of the long arm of human chromosome 17. Southern hybridization to the DNA of these hybrids shows that both genes map near the thymidine kinase gene. In situ hybridization to intact human chromosomes localized both genes to the 17q21-22 region. To better define the physical distance between the two genes, we examined the genomic hybridization pattern of each cDNA probe to high molecular weight restriction fragments separated by pulsed-field gel electrophoresis. Serial hybridizations of the same filter have allowed construction of long-range Mlu I and Sfi I restriction maps spanning more than 500 kilobases. Finally, nonoverlapping portions of the cDNAs for both gpIIb and gpIIIa were used to probe Sfi I digests of genomic DNA separated by field-inversion gels. This confirmed that the genes are physically linked within the same 260-kilobase Sfi I fragment and suggests that the gene for gpIIb is located on the 3' side of the gene for gpIIIa. These results suggest that coordinate expression of gpIIb and gpIIIa may depend on physical proximity.
Animals↗