Publications by authors named "Ollmann M"

Small interfering RNAs (siRNAs) have been successfully used as therapeutics to silence disease-causing genes when conjugated to ligands or formulated in lipid nanoparticles to target relevant cell types for efficacy while sparing other cells for safety. To support the development of new methods for delivery of siRNA therapeutics, we developed and characterized a panel of antibodies generated against chemically modified nucleotides used in therapeutic siRNA molecules, identifying a monoclonal antibody that detects a broad range of siRNA representing distinct sequences and modification patterns. By integrating this anti-siRNA antibody with additional reagents, we created a multiplex siRNA immunoassay that simultaneously quantifies siRNA uptake, trafficking, and silencing activity.

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Small interfering RNA (siRNA) therapeutics have developed rapidly in recent years, despite the challenges associated with delivery of large, highly charged nucleic acids. Delivery of siRNA therapeutics to the liver has been established, with conjugation of siRNA to N-acetylgalactosamine (GalNAc) providing durable gene knockdown in hepatocytes following subcutaneous injection. GalNAc binds the asialoglycoprotein receptor (ASGPR) that is highly expressed on hepatocytes and exploits this scavenger receptor to deliver siRNA across the plasma membrane by endocytosis.

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Human genome wide association studies confirm the association of the rs738409 single nucleotide polymorphism (SNP) in the gene encoding protein patatin like phospholipase domain containing 3 () with nonalcoholic fatty liver disease (NAFLD); the presence of the resulting mutant PNPLA3 I148M protein is a driver of nonalcoholic steatohepatitis (NASH). While -deficient mice do not display an adverse phenotype, the safety of knocking down endogenous wild type in humans remains unknown. To expand the scope of a potential targeted NAFLD therapeutic to both homozygous and heterozygous rs738409 populations, we sought to identify a minor allele-specific small interfering RNA (siRNA).

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Article Synopsis
  • In 2008, guidelines were established for researching autophagy, which has since gained significant interest and new technologies, necessitating regular updates to monitoring methods across various organisms.
  • The new guidelines emphasize selecting appropriate techniques to evaluate autophagy while noting that no single method suits all situations; thus, a combination of methods is encouraged.
  • The document highlights that key proteins involved in autophagy also impact other cellular processes, suggesting genetic studies should focus on multiple autophagy-related genes to fully understand these pathways.
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Article Synopsis
  • This study investigates how adeno-associated virus (AAV) enters cells and reaches the nucleus, which is crucial for its use in gene therapy.
  • Researchers conducted genome-wide screens in U-2 OS cells with AAV2 to identify genes that affect AAV transduction efficiency.
  • They identified specific genes that either enhance or inhibit AAV transduction, with one gene, GPR108, playing a key role in the viral trafficking process and showing selectivity for certain AAV serotypes.
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The discovery of brown adipose tissue (BAT) as a key regulator of energy expenditure has sparked interest in identifying novel soluble factors capable of activating inducible BAT (iBAT) to combat obesity. Using a high content cell-based screen, we identified fibroblast growth factor 16 (FGF16) as a potent inducer of several physical and transcriptional characteristics analogous to those of both "classical" BAT and iBAT. Overexpression of Fgf16 in vivo recapitulated several of our in vitro findings, specifically the significant induction of the Ucp1 gene and UCP1 protein expression in inguinal white adipose tissue (iWAT), a common site for emergent active iBAT.

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Autophagy is the primary process for recycling cellular constituents through lysosomal degradation. In addition to nonselective autophagic engulfment of cytoplasm, autophagosomes can recognize specific cargo by interacting with ubiquitin-binding autophagy receptors such as SQSTM1/p62 (sequestosome 1). This selective form of autophagy is important for degrading aggregation-prone proteins prominent in many neurodegenerative diseases.

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The agouti gene codes for agouti signaling protein (ASP), which is temporally expressed in wild-type mouse follicular melanocytes where it induces pheomelanin synthesis. Studies using purified full-length agouti signaling protein has shown that it competes with (&agr;)-melanocyte stimulating hormone for binding to the melanocortin 1 receptor. We have investigated whether ASP binds exclusively to the melanocortin 1 receptor expressed on mouse melanocytes in primary culture, or additionally activates a receptor that has not been identified yet.

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Agouti protein and Agouti-related protein (Agrp) are paracrine signaling molecules that act by antagonizing the effects of melanocortins, and several alternatives have been proposed to explain their mechanisms of action. Genetic crosses in a sensitized background uncover a phenotypic difference between overexpression of Agouti and loss of Mc1r function, demonstrate that a functional Mc1r is required for the pigmentary effects of Agouti, and suggest that Agouti protein can act as an agonist of the Mc1r in a way that differs from alpha-MSH stimulation. In vitro, Agouti protein inhibits melanocortin action by two mechanisms: competitive antagonism that depends on the carboxyterminus of the protein, and downregulation of melanocortin receptor signaling that depends on the aminoterminus.

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The importance of p53 in carcinogenesis stems from its central role in inducing cell cycle arrest or apoptosis in response to cellular stresses. We have identified a Drosophila homolog of p53 ("Dmp53"). Like mammalian p53, Dmp53 binds specifically to human p53 binding sites, and overexpression of Dmp53 induces apoptosis.

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Agouti-related protein (AGRP) is a recently discovered orexigenic neuropeptide that inhibits the binding and action of alpha-melanocyte-stimulating hormone derived from proopiomelanocortin (POMC) at the melanocortin 3 receptor (MC3R) and melanocortin 4 receptor (MC4R) and has been proposed to function primarily as an endogenous melanocortin antagonist. To better understand the interplay between the AGRP and melanocortin signaling systems, we compared their nerve fiber distributions with each other by immunohistochemistry and their perikarya distribution with MC3R and MC4R by double in situ hybridization. Although deriving from distinct cell groups, AGRP and melanocortin terminals project to identical brain areas.

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Defects in signaling by leptin, a hormone produced primarily by adipose tissue that informs the brain of the body's energy reserves, result in obesity in mice and humans. However, the majority of obese humans do not have abnormalities in leptin or its receptor but instead exhibit leptin resistance that could result from defects in downstream mediators of leptin action. Recently, two potential downstream mediators, agouti-related protein (Agrp) and its receptor, the melanocortin-4 receptor (Mc4r), have been identified.

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Agouti protein and Agouti-related protein (Agrp) regulate pigmentation and body weight, respectively, by antagonizing melanocortin receptor signaling. A carboxyl-terminal fragment of Agouti protein, Ser73-Cys131, is sufficient for melanocortin receptor antagonism, but Western blot analysis of skin extracts reveals that the electrophoretic mobility of native Agouti protein corresponds to the mature full-length form, His23-Cys131. To investigate the potential role of the amino-terminal residues, we compared the function of full-length and carboxyl-terminal fragments of Agrp and Agouti protein in a sensitive bioassay based on pigment dispersion in Xenopus melanophores.

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Agouti-related protein (AGRP) is an orexigenic neuropeptide that acts via central melanocortin receptors, and whose messenger RNA (mRNA) levels are elevated in leptin-deficient mice. Fasting associated with a decline in circulating leptin normally causes a 15-fold elevation of hypothalamic Agrp mRNA levels but has no effect in leptin-deficient mice. Chronic hyperleptinemia associated with the tubby and Cpe(fat) mutations has no effect on Agrp mRNA levels, but short term leptin administration causes a 17% reduction of Agrp mRNA levels in nonmutant mice and a 700% reduction in leptin-deficient mice.

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Recent studies have identified several neuropeptide systems in the hypothalamus that are critical in the regulation of body weight. The lateral hypothalamic area (LHA) has long been considered essential in regulating food intake and body weight. Two neuropeptides, melanin-concentrating hormone (MCH) and the orexins (ORX), are localized in the LHA and provide diffuse innervation of the neuraxis, including monosynaptic projections to the cerebral cortex and autonomic preganglionic neurons.

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Agouti protein and Agouti-related protein (Agrp) are paracrine-signaling molecules that normally regulate pigmentation and body weight, respectively. These proteins antagonize the effects of alpha-melanocyte-stimulating hormone (alpha-MSH) and other melanocortins, and several alternatives have been proposed to explain their biochemical mechanisms of action. We have used a sensitive bioassay based on Xenopus melanophores to characterize pharmacologic properties of recombinant Agouti protein, and have directly measured its cell-surface binding to mammalian cells by use of an epitope-tagged form (HA-Agouti) that retains biologic activity.

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Expression of Agouti protein is normally limited to the skin where it affects pigmentation, but ubiquitous expression causes obesity. An expressed sequence tag was identified that encodes Agouti-related protein, whose RNA is normally expressed in the hypothalamus and whose levels were increased eightfold in ob/ob mice. Recombinant Agouti-related protein was a potent, selective antagonist of Mc3r and Mc4r, melanocortin receptor subtypes implicated in weight regulation.

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Molecular and biochemical mechanisms that switch melanocytes between the production of eumelanin or pheomelanin involve the opposing action of two intercellular signaling molecules, alpha-melanocyte-stimulating hormone (MSH) and agouti signal protein (ASP). In this study, we have characterized the physiological effects of ASP on eumelanogenic melanocytes in culture. Following exposure of black melan-a murine melanocytes to purified recombinant ASP in vitro, pigmentation was markedly inhibited and the production of eumelanosomes was decreased significantly.

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In mouse follicular melanocytes, the switch between eumelanin and pheomelanin synthesis is regulated by the extension locus, which encodes the melanocortin-1 receptor (MC1R) and the agouti locus, which encodes a novel paracrine-signaling molecule that inhibits binding of melanocortins to the MC1R. Human melanocytes express the MC1R and respond to melanotropins with increased proliferation and eumelanogenesis, but a potential role for the human homolog of agouti-signaling protein, ASIP, in human pigmentation has not been investigated. Here we report that ASIP blocked the binding of alpha-melanocyte-stimulating hormone (alpha-MSH) to the MC1R and inhibited the effects of alpha-MSH on human melanocytes.

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Mouse agouti protein is a paracrine signaling molecule that has previously been demonstrated to be an antagonist of melanocortin action at several cloned rodent and human melanocortin receptors. In this study we report the effects of agouti-signaling protein (ASIP), the human homolog of mouse agouti, on the action of alpha-MSH or ACTH at the five known human melanocortin receptor subtypes (hMCR 1-5). When stably expressed in L cells (hMC1R, hMC3R, hMC4R, hMC5R) or in the adrenocortical cell line OS3 (hMC1R, hMC2R, hMC4R), purified recombinant ASIP inhibits the generation of cAMP stimulated by alpha-MSH (hMC1R, hMC3R, hMC4R, hMC5R) or by ACTH (hMC2R).

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The pleiotropic effects of the viable yellow mutation (Avy), an allele of the mouse agouti coat-color locus, include increased susceptibility to spontaneous and chemically induced tumors that affect a wide variety of tissues. As a first step toward understanding the molecular basis of this phenomenon, we established permanent fibroblast-like cell lines from newborn Avy/a and control congenic a/a mice and compared their growth characteristics in vitro. From the VY/WffC3Hf/Nctr and YS/WffCH3f/Nctr-Avy inbre strains, each of which carries the Avy allele on a congenic background, 38 clonal Avy/a and 16 clonal a/a lines were established.

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The mouse agouti coat color gene encodes a novel paracrine signaling molecule whose pulsatile expression produces a characteristic pattern of banded pigment in individual hairs. Several spontaneous agouti alleles produce adult-onset obesity and diabetes, and have provided important single-gene animal models for alterations in energy metabolism. Utilizing linkage groups conserved between mice and humans, we have cloned the human homolog of the mouse agouti gene from a human chromosome 20 yeast artificial chromosome known to contain S-adenosyl homocysteine hydrolase (AHCY).

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In a previous survey of endogenous proviruses among inbred mouse strains, the Xmv-10 provirus was found only in strains that carried the non-agouti (a) mutation (Frankel et al. J. Virol.

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The mouse agouti gene controls the deposition of yellow and black pigment in developing hairs. Several dominant alleles, including lethal yellow (Ay), result in the exclusive production of yellow pigment and have pleiotropic effects that include obesity and increased tumor susceptibility. In an interspecific backcross, we established genetic limits for the agouti gene and found that the Ay and the lethal non-agouti (ax) allele were not separated from a previously identified probe at the breakpoint of the Is1GsO chromosomal rearrangement.

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The region surrounding the agouti coat color locus on mouse Chromosome 2 contains several genes required for peri-implantation development, limb morphogenesis, and segmentation of the nervous system. We have applied radiation hybrid mapping, a somatic cell genetic technique for constructing long-range maps of mammalian chromosomes, to eight molecular markers in this region. Using a mathematical model to estimate the frequency of radiation-induced breakage, we have constructed a map that spans approximately 20 recombination units and 475 centirays8000.

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