The Experts below are selected from a list of 216 Experts worldwide ranked by ideXlab platform
Stephan M Tanner - One of the best experts on this subject based on the ideXlab platform.
-
PLENARY PAPER The functional cobalamin (vitamin B12)–intrinsic factor receptor is a novel complex of cubilin and Amnionless
2016Co-Authors: John C Fyfe, Stephan M Tanner, Mette Madsen, Albert De La Chapelle, Peter Hojrup, Erik I Christensen, Soren K MoestrupAbstract:Imerslund-Gräsbeck syndrome (I-GS, megaloblastic anemia 1) is an autosomal recessive disorder characterized by intes-tinal cobalamin (vitamin B12) malabsorp-tion and proteinuria. I-GS–causing muta-tions are found in either of 2 genes encoding the epithelial proteins: cubilin and Amnionless (AMN). Cubilin recog-nizes intrinsic factor (IF)–cobalamin and various other proteins to be endocytosed in the intestine and kidney, respectively, whereas the function of AMN is unknown. Here we show that cubilin and AMN colo-calize in the endocytic apparatus of polar-ized epithelial cells and copurify as a tight complex during IF-cobalamin affinity and nondenaturing gel filtration chromatogra-phy. In transfected cells expressing either AMN or a truncated IF-cobalamin–binding cubilin construct, neither protein alone conferred ligand endocytosis. In cubilin transfectants, cubilin accumulated in early biosynthetic compartments. However, in cells cotransfected with AMN and the cubilin construct, cubilin trafficked to the cell surface and endosomes, and the cells exhibited IF-cobalamin endocytosis and lysosomal degradation of IF. These data indicate that cubilin and AMN are sub-units of a novel cubilin/AMN (cubam) com-plex, where AMN binds to the amino-terminal third of cubilin and directs subcellular localization and endocytosis of cubilin with its ligand. Therefore, muta-tions affecting either of the 2 proteins may abrogate function of the cubam com
-
Amnionless amn mutations in imerslund grasbeck syndrome may be associated with disturbed vitamin b12 transport into the cns
Journal of Inherited Metabolic Disease, 2008Co-Authors: A S Luder, Stephan M Tanner, A De La Chapelle, J H WalterAbstract:Familial selective vitamin B12 (cobalamin, Cbl) malabsorption (Imerslund–Grasbeck syndrome, IGS, OMIM 261100) is a group of autosomal recessive disorders characterized by selective malabsorption of Cbl from the terminal ileum in the presence of normal histology. Mutations in the Amnionless (AMN) and cubilin (CUBN) genes are known to be causes of IGS. Their gene products combine to form a receptor complex (cubam), which is instrumental in the binding and transport of Cbl in the gut. As opposed to Cbl transport in the terminal ileum, normal transport of Cbl into the CNS is poorly understood and little is known regarding its molecular basis. Studies in adults with neuropsychiatric disease have suggested the presence of an active transport mechanism into the central nervous system constituting a blood–brain barrier (BBB) for Cbl. A child with IGS, compound heterozygous for a missense and a nonsense mutation in the Amnionless (AMN) protein gene, was noted to have a high daily cobalamin (Cbl) requirement for neuropsychiatric, but not for systemic metabolic and haematological, remission. Measurements of CSF Cbl revealed evidence that the transport of Cbl into the central nervous system was impaired, and a standard Schilling test was consistent with a dose response of cobalamin transport across the terminal ileum. Amnionless protein is known to be expressed in the fetal and postnatal central nervous system, and is known to be involved in Cbl transport in other tissues such as kidney as well as the gut. It is possible that an active Cbl transport mechanism at the BBB exists, and that the Amnionless (AMN) protein may be part of this mechanism, as it is in cobalamin transport in the terminal ileum.
-
Amnionless function is required for cubilin brush border expression and intrinsic factor cobalamin vitamin b12 absorption in vivo
Blood, 2005Co-Authors: Qianchuan He, Adam Kilkenney, Brittany L Gregory, Erik Ilsø Christensen, Alejandro A Schaffer, Henrik Vorum, Ewen F. Kirkness, Mette Madsen, Peter Hojrup, Stephan M TannerAbstract:Amnionless (AMN) and cubilin gene products appear to be essential functional subunits of an endocytic receptor called cubam. Mutation of either gene causes autosomal recessive Imerslund-Grasbeck syndrome (I-GS, OMIM no. 261100) in humans, a disorder characterized by selective intestinal malabsorption of cobalamin (vitamin B12) and urinary loss of several specific low-molecular-weight proteins. Vital insight into the molecular pathology of I-GS has been obtained from studies of dogs with a similar syndrome. In this work, we show that I-GS segregates in a large canine kindred due to an in-frame deletion of 33 nucleotides in exon 10 of AMN. In a second, unrelated I-GS kindred, affected dogs exhibit a homozygous substitution in the AMN translation initiation codon. Studies in vivo demonstrated that both mutations abrogate AMN expression and block cubilin processing and targeting to the apical membrane. The essential features of AMN dysfunction observed in vivo are recapitulated in a heterologous cell-transfection system, thus validating the system for analysis of AMN-cubilin interactions. Characterization of canine AMN mutations that cause I-GS establishes the canine model as an ortholog of the human disorder well suited to studies of AMN function and coevolution with cubilin. (Blood. 2005;106:1447-1453)
-
hereditary juvenile cobalamin deficiency caused by mutations in the intrinsic factor gene
Proceedings of the National Academy of Sciences of the United States of America, 2005Co-Authors: Stephan M Tanner, James D Perko, C Oner, Mualla Cetin, Cigdem Altay, Zekiye Yurtsever, Karen L David, Laurence Faivre, Essam A R Ismail, Ralph GrasbeckAbstract:Hereditary juvenile megaloblastic anemia due to vitamin B12 (cobalamin) deficiency is caused by intestinal malabsorption of cobalamin. In Imerslund–Grasbeck syndrome (IGS), cobalamin absorption is completely abolished and not corrected by the administration of intrinsic factor (IF); if untreated, the disease is fatal. Biallelic mutations either in the cubilin (CUBN) or Amnionless (AMN) gene cause IGS. In a series of families clinically diagnosed with likely IGS, at least six displayed no evidence of mutations in CUBN or AMN. A genome-wide search for linkage followed by mutational analysis of candidate genes was performed in five of these families. A region in chromosome 11 showed evidence of linkage in four families. The gastric IF (GIF) gene located in this region harbored homozygous nonsense and missense mutations in these four families and in three additional families. The disease in these cases therefore should be classified as hereditary IF deficiency. Clinically, these patients resembled those with typical IGS; radiocobalamin absorption tests had been inconclusive regarding the nature of the defect. In the diagnosis of juvenile cobalamin deficiency, mutational analysis of the CUBN, AMN, and GIF genes provides a molecular characterization of the underlying defect and may be the diagnostic method of choice.
-
genetically heterogeneous selective intestinal malabsorption of vitamin b12 founder effects consanguinity and high clinical awareness explain aggregations in scandinavia and the middle east
Human Mutation, 2004Co-Authors: Stephan M Tanner, C Oner, Mualla Cetin, Essam A R Ismail, Ryan Bisson, Ceren Acar, R Oner, Mohamed Abdelaal, Willy Lissens, Ralf KraheAbstract:Selective intestinal malabsorption of vitamin B12 causing juvenile megaloblastic anemia (MGA; MIM# 261100) is a recessively inherited disorder that is believed to be rare except for notable clusters of cases in Finland, Norway, and the Eastern Mediterranean region. The disease can be caused by mutations in either the cubilin (CUBN; MGA1; MIM# 602997) or the Amnionless (AMN; MIM# 605799) gene. To explain the peculiar geographical distribution, we hypothesized that mutations in one of the genes would mainly be responsible for the disease in Scandinavia, and mutations in the other gene in the Mediterranean region. We studied 42 sibships and found all cases in Finland to be due to CUBN (three different mutations) and all cases in Norway to be due to AMN (two different mutations), while in Turkey, Israel, and Saudi Arabia, there were two different AMN mutations and three different CUBN mutations. Haplotype evidence excluded both CUBN and AMN conclusively in five families and tentatively in three families, suggesting the presence of at least one more gene locus that can cause MGA. We conclude that the Scandinavian cases are typical examples of enrichment by founder effects, while in the Mediterranean region high degrees of consanguinity expose rare mutations in both genes. We suggest that in both regions, physician awareness of this disease causes it to be more readily diagnosed than elsewhere; thus, it may well be more common worldwide than previously thought. Hum Mutat 23:327–333, 2004 © 2004 Wiley-Liss, Inc.
Mette Madsen - One of the best experts on this subject based on the ideXlab platform.
-
structural assembly of the megadalton sized receptor for intestinal vitamin b12 uptake and kidney protein reabsorption
Nature Communications, 2018Co-Authors: Casper K Larsen, Mette Madsen, Anders Etzerodt, Karsten Skjødt, Soren K Moestrup, Christian Brix Folsted AndersenAbstract:The endocytic receptor cubam formed by the 460-kDa protein cubilin and the 45-kDa transmembrane protein Amnionless (AMN), is essential for intestinal vitamin B12 (B12) uptake and for protein (e.g. albumin) reabsorption from the kidney filtrate. Loss of function of any of the two components ultimately leads to serious B12 deficiency and urinary protein loss in humans (Imerslund-Grasbeck’s syndrome, IGS). Here, we present the crystal structure of AMN in complex with the amino-terminal region of cubilin, revealing a sophisticated assembly of three cubilin subunits combining into a single intertwined β-helix domain that docks to a corresponding three-faced β-helix domain in AMN. This β-helix-β-helix association thereby anchors three ligand-binding cubilin subunits to the transmembrane AMN. Electron microscopy of full-length cubam reveals a 700–800 A long tree-like structure with the potential of dimerization into an even larger complex. Furthermore, effects of known human mutations causing IGS are explained by the structural information. Cubilin and the transmembrane protein Amnionless (AMN) form the endocytic receptor cubam that is essential for intestinal vitamin B12 uptake. Here the authors present the 2.3 A crystal structure of AMN in complex with the amino-terminal region of cubilin and discuss cubam architecture and disease causing mutations.
-
Structural assembly of the megadalton-sized receptor for intestinal vitamin B12 uptake and kidney protein reabsorption
Nature Publishing Group, 2018Co-Authors: Casper Larsen, Søren Kragh Moestrup, Mette Madsen, Anders Etzerodt, Karsten Skjødt, Christian Brix Folsted AndersenAbstract:Cubilin and the transmembrane protein Amnionless (AMN) form the endocytic receptor cubam that is essential for intestinal vitamin B12 uptake. Here the authors present the 2.3 Å crystal structure of AMN in complex with the amino-terminal region of cubilin and discuss cubam architecture and disease causing mutations
-
PLENARY PAPER The functional cobalamin (vitamin B12)–intrinsic factor receptor is a novel complex of cubilin and Amnionless
2016Co-Authors: John C Fyfe, Stephan M Tanner, Mette Madsen, Albert De La Chapelle, Peter Hojrup, Erik I Christensen, Soren K MoestrupAbstract:Imerslund-Gräsbeck syndrome (I-GS, megaloblastic anemia 1) is an autosomal recessive disorder characterized by intes-tinal cobalamin (vitamin B12) malabsorp-tion and proteinuria. I-GS–causing muta-tions are found in either of 2 genes encoding the epithelial proteins: cubilin and Amnionless (AMN). Cubilin recog-nizes intrinsic factor (IF)–cobalamin and various other proteins to be endocytosed in the intestine and kidney, respectively, whereas the function of AMN is unknown. Here we show that cubilin and AMN colo-calize in the endocytic apparatus of polar-ized epithelial cells and copurify as a tight complex during IF-cobalamin affinity and nondenaturing gel filtration chromatogra-phy. In transfected cells expressing either AMN or a truncated IF-cobalamin–binding cubilin construct, neither protein alone conferred ligand endocytosis. In cubilin transfectants, cubilin accumulated in early biosynthetic compartments. However, in cells cotransfected with AMN and the cubilin construct, cubilin trafficked to the cell surface and endosomes, and the cells exhibited IF-cobalamin endocytosis and lysosomal degradation of IF. These data indicate that cubilin and AMN are sub-units of a novel cubilin/AMN (cubam) com-plex, where AMN binds to the amino-terminal third of cubilin and directs subcellular localization and endocytosis of cubilin with its ligand. Therefore, muta-tions affecting either of the 2 proteins may abrogate function of the cubam com
-
RESEARCH ARTICLE Open Access Detailed investigations of proximal tubular
2016Co-Authors: Tina Storm, Sabine Amsellem, Rikke Nielsen, P Verroust, Mette Madsen, Christina Zeitz, Department Of Biomedicine, Denmarkcharacteristic Low-molecular-weight Proteinuria. Heidi Koldsø, Jens Michael Hertz, Erik I ChristensenAbstract:Background: Imerslund-Gräsbeck Syndrome (IGS) is a rare genetic disorder characterised by juvenile megaloblastic anaemia. IGS is caused by mutations in either of the genes encoding the intestinal intrinsic factor-vitamin B12 receptor complex, cubam. The cubam receptor proteins cubilin and Amnionless are both expressed in the small intestine as well as the proximal tubules of the kidney and exhibit an interdependent relationship for post-translational processing and trafficking. In the proximal tubules cubilin is involved in the reabsorption of several filtered plasma proteins including vitamin carriers and lipoproteins. Consistent with this, low-molecular-weight proteinuria has been observed in most patients with IGS. The aim of this study was to characterise novel disease-causing mutations and correlate novel and previously reported mutations with the presence of low-molecular-weight proteinuria. Methods: Genetic screening was performed by direct sequencing of the CUBN and AMN genes and novel identified mutations were characterised by in silico and/or in vitro investigations. Urinary protein excretion was analysed by immunoblotting and high-resolution gel electrophoresis of collected urines from patients and healthy controls to determine renal phenotype. Results: Genetic characterisation of nine IGS patients identified two novel AMN frameshift mutations alongside a frequently reported AMN splice site mutation and two CUBN missense mutations; one novel and one previousl
-
lack of megalin expression in adult human terminal ileum suggests megalin independent cubilin Amnionless activity during vitamin b12 absorption
Physiological Reports, 2014Co-Authors: Louise L Jensen, Rikke Katrine Andersen, Henrik Hager, Mette MadsenAbstract:Cubilin plays an essential role in terminal ileum and renal proximal tubules during absorption of vitamin B12 and ligands from the glomerular ultrafiltrate. Cubilin is coexpressed with Amnionless, and cubilin and Amnionless are mutually dependent on each other for correct processing to the plasma membrane upon synthesis. Patients with defects in either protein suffer from vitamin B12-malabsorption and in some cases proteinuria. Cubilin lacks a transmembrane region and signals for endocytosis and is dependent on a transmembrane coreceptor during internalization. Amnionless has been shown to be able to mediate internalization of cubilin in a cell-based model system. Cubilin has additionally been suggested to function together with megalin, and a recent study of megalin-deficient patients indicates that uptake of cubilin ligands in the kidney is critically dependent on megalin. To further investigate the potential role of Amnionless and megalin in relation to cubilin function in terminal ileum and vitamin B12 uptake, we initiated a study of CUBN/cubilin, AMN/Amnionless, and LRP2/megalin expression in adult human terminal ileum. Our study is the first to reveal the expression pattern of cubilin, Amnionless, and megalin in adult human terminal ileum, where cubilin and Amnionless localize to the epithelial cells. Surprisingly, we did not detect any megalin protein in adult terminal ileum and consistently, only extremely low amounts of LRP2 mRNA. Our data therefore advocate that cubilin and Amnionless act independently of megalin in adult terminal ileum and that the cubilin-megalin interdependency accordingly should be considered as tissue and ligand specific.
Ralph Grasbeck - One of the best experts on this subject based on the ideXlab platform.
-
imerslund grasbeck syndrome selective vitamin b12 malabsorption with proteinuria
Orphanet Journal of Rare Diseases, 2006Co-Authors: Ralph GrasbeckAbstract:Imerslund-Grasbeck syndrome (IGS) or selective vitamin B12 (cobalamin) malabsorption with proteinuria is a rare autosomal recessive disorder characterized by vitamin B12 deficiency commonly resulting in megaloblastic anemia, which is responsive to parenteral vitamin B12 therapy and appears in childhood. Other manifestations include failure to thrive and grow, infections and neurological damage. Mild proteinuria (with no signs of kidney disease) is present in about half of the patients. Anatomical anomalies in the urinary tract were observed in some Norwegian patients. Vitamin B12 absorption tests show low absorption, not corrected by administration of intrinsic factor. The symptoms appear from 4 months (not immediately after birth as in transcobalamin deficiency) up to several years after birth. The syndrome was first described in Finland and Norway where the prevalence is about 1:200,000. The cause is a defect in the receptor of the vitamin B12-intrinsic factor complex of the ileal enterocyte. In most cases, the molecular basis of the selective malabsorption and proteinuria involves a mutation in one of two genes, cubilin (CUBN) on chromosome 10 or Amnionless (AMN) on chromosome 14. Both proteins are components of the intestinal receptor for the vitamin B12-intrinsic factor complex and the receptor mediating the tubular reabsorption of protein from the primary urine. Management includes life-long vitamin B12 injections, and with this regimen, the patients stay healthy for decades. However, the proteinuria persists. In diagnosing this disease, it is important to be aware that cobalamin deficiency affects enterocyte function; therefore, all tests suggesting general and cobalamin malabsorption should be repeated after abolishment of the deficiency.
-
imerslund grasbeck syndrome selective vitamin b 12 malabsorption with proteinuria
Orphanet Journal of Rare Diseases, 2006Co-Authors: Ralph GrasbeckAbstract:Imerslund-Grasbeck syndrome (IGS) or selective vitamin B12 (cobalamin) malabsorption with proteinuria is a rare autosomal recessive disorder characterized by vitamin B12 deficiency commonly resulting in megaloblastic anemia, which is responsive to parenteral vitamin B12 therapy and appears in childhood. Other manifestations include failure to thrive and grow, infections and neurological damage. Mild proteinuria (with no signs of kidney disease) is present in about half of the patients. Anatomical anomalies in the urinary tract were observed in some Norwegian patients. Vitamin B12 absorption tests show low absorption, not corrected by administration of intrinsic factor. The symptoms appear from 4 months (not immediately after birth as in transcobalamin deficiency) up to several years after birth. The syndrome was first described in Finland and Norway where the prevalence is about 1:200,000. The cause is a defect in the receptor of the vitamin B12-intrinsic factor complex of the ileal enterocyte. In most cases, the molecular basis of the selective malabsorption and proteinuria involves a mutation in one of two genes, cubilin (CUBN) on chromosome 10 or Amnionless (AMN) on chromosome 14. Both proteins are components of the intestinal receptor for the vitamin B12-intrinsic factor complex and the receptor mediating the tubular reabsorption of protein from the primary urine. Management includes life-long vitamin B12 injections, and with this regimen, the patients stay healthy for decades. However, the proteinuria persists. In diagnosing this disease, it is important to be aware that cobalamin deficiency affects enterocyte function; therefore, all tests suggesting general and cobalamin malabsorption should be repeated after abolishment of the deficiency.
-
Orphanet Journal of Rare Diseases BioMed Central Review
2006Co-Authors: Imerslund-gräsbeck Syndrome Vitamin B, Ralph GrasbeckAbstract:which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Imerslund-Gräsbeck syndrome (IGS) or selective vitamin B 12 (cobalamin) malabsorption with proteinuria is a rare autosomal recessive disorder characterized by vitamin B 12 deficiency commonly resulting in megaloblastic anemia, which is responsive to parenteral vitamin B 12 therapy and appears in childhood. Other manifestations include failure to thrive and grow, infections and neurological damage. Mild proteinuria (with no signs of kidney disease) is present in about half of the patients. Anatomical anomalies in the urinary tract were observed in some Norwegian patients. Vitamin B 12 absorption tests show low absorption, not corrected by administration of intrinsic factor. The symptoms appear from 4 months (not immediately after birth as in transcobalamin deficiency) up to several years after birth. The syndrome was first described in Finland and Norway where the prevalence is about 1:200,000. The cause is a defect in the receptor of the vitamin B 12-intrinsic factor complex of the ileal enterocyte. In most cases, the molecular basis of the selective malabsorption and proteinuria involves a mutation in one of two genes, cubilin (CUBN) on chromosome 10 or Amnionless (AMN) on chromosome 14. Both proteins are components of th
-
hereditary juvenile cobalamin deficiency caused by mutations in the intrinsic factor gene
Proceedings of the National Academy of Sciences of the United States of America, 2005Co-Authors: Stephan M Tanner, James D Perko, C Oner, Mualla Cetin, Cigdem Altay, Zekiye Yurtsever, Karen L David, Laurence Faivre, Essam A R Ismail, Ralph GrasbeckAbstract:Hereditary juvenile megaloblastic anemia due to vitamin B12 (cobalamin) deficiency is caused by intestinal malabsorption of cobalamin. In Imerslund–Grasbeck syndrome (IGS), cobalamin absorption is completely abolished and not corrected by the administration of intrinsic factor (IF); if untreated, the disease is fatal. Biallelic mutations either in the cubilin (CUBN) or Amnionless (AMN) gene cause IGS. In a series of families clinically diagnosed with likely IGS, at least six displayed no evidence of mutations in CUBN or AMN. A genome-wide search for linkage followed by mutational analysis of candidate genes was performed in five of these families. A region in chromosome 11 showed evidence of linkage in four families. The gastric IF (GIF) gene located in this region harbored homozygous nonsense and missense mutations in these four families and in three additional families. The disease in these cases therefore should be classified as hereditary IF deficiency. Clinically, these patients resembled those with typical IGS; radiocobalamin absorption tests had been inconclusive regarding the nature of the defect. In the diagnosis of juvenile cobalamin deficiency, mutational analysis of the CUBN, AMN, and GIF genes provides a molecular characterization of the underlying defect and may be the diagnostic method of choice.
Albert De La Chapelle - One of the best experts on this subject based on the ideXlab platform.
-
PLENARY PAPER The functional cobalamin (vitamin B12)–intrinsic factor receptor is a novel complex of cubilin and Amnionless
2016Co-Authors: John C Fyfe, Stephan M Tanner, Mette Madsen, Albert De La Chapelle, Peter Hojrup, Erik I Christensen, Soren K MoestrupAbstract:Imerslund-Gräsbeck syndrome (I-GS, megaloblastic anemia 1) is an autosomal recessive disorder characterized by intes-tinal cobalamin (vitamin B12) malabsorp-tion and proteinuria. I-GS–causing muta-tions are found in either of 2 genes encoding the epithelial proteins: cubilin and Amnionless (AMN). Cubilin recog-nizes intrinsic factor (IF)–cobalamin and various other proteins to be endocytosed in the intestine and kidney, respectively, whereas the function of AMN is unknown. Here we show that cubilin and AMN colo-calize in the endocytic apparatus of polar-ized epithelial cells and copurify as a tight complex during IF-cobalamin affinity and nondenaturing gel filtration chromatogra-phy. In transfected cells expressing either AMN or a truncated IF-cobalamin–binding cubilin construct, neither protein alone conferred ligand endocytosis. In cubilin transfectants, cubilin accumulated in early biosynthetic compartments. However, in cells cotransfected with AMN and the cubilin construct, cubilin trafficked to the cell surface and endosomes, and the cells exhibited IF-cobalamin endocytosis and lysosomal degradation of IF. These data indicate that cubilin and AMN are sub-units of a novel cubilin/AMN (cubam) com-plex, where AMN binds to the amino-terminal third of cubilin and directs subcellular localization and endocytosis of cubilin with its ligand. Therefore, muta-tions affecting either of the 2 proteins may abrogate function of the cubam com
-
the functional cobalamin vitamin b12 intrinsic factor receptor is a novel complex of cubilin and Amnionless
Blood, 2004Co-Authors: John C Fyfe, Quianchuan He, Stephan M Tanner, Erik Ilsø Christensen, Mette Madsen, Albert De La Chapelle, Peter Hojrup, Søren Kragh MoestrupAbstract:Imerslund-Grasbeck syndrome (I-GS, megaloblastic anemia 1) is an autosomal recessive disorder characterized by intestinal cobalamin (vitamin B 12 ) malabsorption and proteinuria. I-GS–causing mutations are found in either of 2 genes encoding the epithelial proteins: cubilin and Amnionless (AMN). Cubilin recognizes intrinsic factor (IF)–cobalamin and various other proteins to be endocytosed in the intestine and kidney, respectively, whereas the function of AMN is unknown. Here we show that cubilin and AMN colocalize in the endocytic apparatus of polarized epithelial cells and copurify as a tight complex during IF-cobalamin affinity and nondenaturing gel filtration chromatography. In transfected cells expressing either AMN or a truncated IF-cobalamin–binding cubilin construct, neither protein alone conferred ligand endocytosis. In cubilin transfectants, cubilin accumulated in early biosynthetic compartments. However, in cells cotransfected with AMN and the cubilin construct, cubilin trafficked to the cell surface and endosomes, and the cells exhibited IF-cobalamin endocytosis and lysosomal degradation of IF. These data indicate that cubilin and AMN are subunits of a novel cubilin/AMN (cubam) complex, where AMN binds to the amino-terminal third of cubilin and directs subcellular localization and endocytosis of cubilin with its ligand. Therefore, mutations affecting either of the 2 proteins may abrogate function of the cubam complex and cause IG-S.
-
Amnionless essential for mouse gastrulation is mutated in recessive hereditary megaloblastic anemia
Nature Genetics, 2003Co-Authors: Stephan M Tanner, Orit Massika, Anne Saarinen, Hanna Mandel, Mervi Kuronen, Maria Aminoff, Sandya Liyanarachchi, Harald Broch, Fred A Wright, Albert De La ChapelleAbstract:Amnionless, essential for mouse gastrulation, is mutated in recessive hereditary megaloblastic anemia
-
Amnionless essential for mouse gastrulation is mutated in recessive hereditary megaloblastic anemia
Nature Genetics, 2003Co-Authors: Stephan M Tanner, Orit Massika, Anne Saarinen, Hanna Mandel, Mervi Kuronen, Maria Aminoff, Sandya Liyanarachchi, Harald Broch, Fred A Wright, Albert De La ChapelleAbstract:The Amnionless gene, Amn, on mouse chromosome 12 encodes a type I transmembrane protein that is expressed in the extraembryonic visceral layer during gastrulation. Mice homozygous with respect to the amn mutation generated by a transgene insertion have no amnion. The embryos are severely compromised, surviving to the tenth day of gestation but seem to lack the mesodermal layers that normally produce the trunk. The Amn protein has one transmembrane domain separating a larger, N-terminal extracellular region and a smaller, C-terminal cytoplasmic region. The extracellular region harbors a cysteine-rich domain resembling those occurring in Chordin, found in Xenopus laevis embryos, and Sog, found in Drosophila melanogaster. As these cysteine-rich domains bind bone morphogenetic proteins (Bmps), it has been speculated that the cysteine-rich domain in Amn also binds Bmps. We show that homozygous mutations affecting exons 1-4 of human AMN lead to selective malabsorption of vitamin B12 (a phenotype associated with megaloblastic anemia 1, MGA1; OMIM 261100; refs. 5,6) in otherwise normal individuals, suggesting that the 5' end of AMN is dispensable for embryonic development but necessary for absorption of vitamin B12. When the 5' end of AMN is truncated by mutations, translation is initiated from alternative downstream start codons.
Richard H Finnell - One of the best experts on this subject based on the ideXlab platform.
-
Microarray analysis of E9.5 reduced folate carrier () knockout embryos reveals altered expression of genes in the cubilin-megalin multiligand endocytic receptor complex-2
2011Co-Authors: Janee Gelineau-van Waes, Justin Wilberding, Linda K Bauer, James D. Eudy, Lynette M Smith, Joyce R Maddox, Michael Van Waes, Richard H FinnellAbstract:consisting of a large extracellular region, a single transmembrane domain, and a C-terminal cytoplasmic tail. The extracellular domain of megalin contains four clusters of lipoprotein receptor ligand-binding repeats (blue), growth factor repeats, an EGF repeat, and YWTD spacer regions. The second cluster of ligand-binding repeats has been identified as a common binding site for several ligands including apolipoprotein E (Apo E), apolipoprotein M (Apo M), retinol binding protein (Rbp), and transthyretin (Ttr). Megalin also binds the soluble form of the folate receptor (Folr1), and the morphogen sonic hedgehog (Shh). The cytoplasmic tail of megalin binds Dab2, a cytosolic adapter protein important for megalin-mediated endocytosis, and Dab2 binds and recruits Myo6 to clathrin-coated vesicles. The receptor-associated protein (Lrpap1; RAP) binds both megalin and cubilin. Cubilin is a peripheral membrane receptor comprised of a short amino terminal, eight EGF type domains, and 27 CUB domains (green). The amino-terminal end of cubilin is attached to the extracellular part of Amnionless (Amn), and Amnionless provides the transmembrane domain necessary for the anchoring and endocytic trafficking of cubilin. Cubilin ligands include transferring (Trf), albumin, hemoglobin, apolipoprotein A1 (ApoA1), and intrinsic factor (IF)-vitamin B.Copyright information:Taken from "Microarray analysis of E9.5 reduced folate carrier () knockout embryos reveals altered expression of genes in the cubilin-megalin multiligand endocytic receptor complex"http://www.biomedcentral.com/1471-2164/9/156BMC Genomics 2008;9():156-156.Published online 9 Apr 2008PMCID:PMC2383917.
-
microarray analysis of e9 5 reduced folate carrier rfc1 slc19a1 knockout embryos reveals altered expression of genes in the cubilin megalin multiligand endocytic receptor complex
BMC Genomics, 2008Co-Authors: Janee Gelineau-van Waes, Justin Wilberding, Linda K Bauer, Michael Van Waes, J Maddox, James D. Eudy, Lynette M Smith, Richard H FinnellAbstract:The reduced folate carrier (RFC1) is an integral membrane protein and facilitative anion exchanger that mediates delivery of 5-methyltetrahydrofolate into mammalian cells. Adequate maternal-fetal transport of folate is necessary for normal embryogenesis. Targeted inactivation of the murine RFC1 gene results in post-implantation embryolethality, but daily folic acid supplementation of pregnant dams prolongs survival of homozygous embryos until mid-gestation. At E10.5 RFC1-/- embryos are developmentally delayed relative to wildtype littermates, have multiple malformations, including neural tube defects, and die due to failure of chorioallantoic fusion. The mesoderm is sparse and disorganized, and there is a marked absence of erythrocytes in yolk sac blood islands. The identification of alterations in gene expression and signaling pathways involved in the observed dysmorphology following inactivation of RFC1-mediated folate transport are the focus of this investigation. Affymetrix microarray analysis of the relative gene expression profiles in whole E9.5 RFC1-/- vs. RFC1+/+ embryos identified 200 known genes that were differentially expressed. Major ontology groups included transcription factors (13.04%), and genes involved in transport functions (ion, lipid, carbohydrate) (11.37%). Genes that code for receptors, ligands and interacting proteins in the cubilin-megalin multiligand endocytic receptor complex accounted for 9.36% of the total, followed closely by several genes involved in hematopoiesis (8.03%). The most highly significant gene network identified by Ingenuity™ Pathway analysis included 12 genes in the cubilin-megalin multiligand endocytic receptor complex. Altered expression of these genes was validated by quantitative RT-PCR, and immunohistochemical analysis demonstrated that megalin protein expression disappeared from the visceral yolk sac of RFC1-/- embryos, while cubilin protein was widely misexpressed. Inactivation of RFC1 impacts the expression of several ligands and interacting proteins in the cubilin-Amnionless-megalin complex that are involved in the maternal-fetal transport of folate and other nutrients, lipids and morphogens such as sonic hedgehog (Shh) and retinoids that play critical roles in normal embryogenesis.
-
Microarray analysis of E9.5 reduced folate carrier (RFC1; Slc19a1) knockout embryos reveals altered expression of genes in the cubilin-megalin multiligand endocytic receptor complex
BMC Genomics, 2008Co-Authors: Janee Gelineau-van Waes, Justin Wilberding, Linda K Bauer, James D. Eudy, Lynette M Smith, Joyce R Maddox, Michael Van Waes, Richard H FinnellAbstract:Background The reduced folate carrier ( RFC1 ) is an integral membrane protein and facilitative anion exchanger that mediates delivery of 5-methyltetrahydrofolate into mammalian cells. Adequate maternal-fetal transport of folate is necessary for normal embryogenesis. Targeted inactivation of the murine RFC1 gene results in post-implantation embryolethality, but daily folic acid supplementation of pregnant dams prolongs survival of homozygous embryos until mid-gestation. At E10.5 RFC1 ^-/- embryos are developmentally delayed relative to wildtype littermates, have multiple malformations, including neural tube defects, and die due to failure of chorioallantoic fusion. The mesoderm is sparse and disorganized, and there is a marked absence of erythrocytes in yolk sac blood islands. The identification of alterations in gene expression and signaling pathways involved in the observed dysmorphology following inactivation of RFC1-mediated folate transport are the focus of this investigation. Results Affymetrix microarray analysis of the relative gene expression profiles in whole E9.5 RFC1 ^-/- vs. RFC1 ^+/+ embryos identified 200 known genes that were differentially expressed. Major ontology groups included transcription factors (13.04%), and genes involved in transport functions (ion, lipid, carbohydrate) (11.37%). Genes that code for receptors, ligands and interacting proteins in the cubilin-megalin multiligand endocytic receptor complex accounted for 9.36% of the total, followed closely by several genes involved in hematopoiesis (8.03%). The most highly significant gene network identified by Ingenuity™ Pathway analysis included 12 genes in the cubilin-megalin multiligand endocytic receptor complex. Altered expression of these genes was validated by quantitative RT-PCR, and immunohistochemical analysis demonstrated that megalin protein expression disappeared from the visceral yolk sac of RFC1 ^-/- embryos, while cubilin protein was widely misexpressed. Conclusion Inactivation of RFC1 impacts the expression of several ligands and interacting proteins in the cubilin-Amnionless-megalin complex that are involved in the maternal-fetal transport of folate and other nutrients, lipids and morphogens such as sonic hedgehog (Shh) and retinoids that play critical roles in normal embryogenesis.