Cobalamin (vitamin B 12) is an essential micronutrient for the maintenance of normal metabolism. Humans and other animals have evolved a highly specific mechanism for concentrating dietary cobalamin on the absorptive surface of distal small intestinal enterocytes. Cobalamin endocytosis is mediated by cubilin, a large multiligand receptor of the apical membrane. Imerslund-Grasbeck syndrome (I-GS) is an autosomal recessive trait of selective cobalamin malabsorption and proteinuria due to failure to express functional cubilin in the apical membrane of ileal enterocytes and renal proximal tubule cells. Cubilin mutations cause human I-GS in one population, but other causes remain to be determined. An inherited defect of cubilin trafficking to the apical membrane has been described in a canine I-GS model, but cubilin was excluded as the disease gene, indicating that an unknown accessory activity is essential for polarized cubilin expression in intestinal and renal epithelial cells. Our goal is to take advantage of this unique, naturally-occurring animal model to better understand the cell biology of receptor expression in polarized epithelia. Lacking functional gene candidates, we initiated a comparative positional-candidate gene approach to determine the I-GS disease gene. Significant linkage to a gene marker was found, defining an approximately 9 cM region harboring the disease locus.
The specific aims of this proposal are: 1) to minimize the region of linkage by developing and applying new genetic markers to a large outbred linkage pedigree in order to identify a subset of genes in the homologous region of the human genome as positional candidates; 2) to clone and analyze positional candidates for mutations; and 3) to initiate functional analyses of the disease-causing gene product. Genes will be chosen for new marker development in an interative process from the locality of markers showing close linkage to the disease locus until a gene marker is found which exhibits no recombination with the disease locus. The I-GS gene will be identified by mutation analysis, and antibody will be generated to study intracellular localization and determine binding partners. Results of these efforts are expected to open a window onto a new aspect of nutrient absorption and membrane receptor biology.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Exploratory/Developmental Grants (R21)
Project #
1R21DK064161-01
Application #
6598635
Study Section
Nutrition Study Section (NTN)
Program Officer
May, Michael K
Project Start
2003-05-01
Project End
2005-04-30
Budget Start
2003-05-01
Budget End
2004-04-30
Support Year
1
Fiscal Year
2003
Total Cost
$145,374
Indirect Cost
Name
Michigan State University
Department
Microbiology/Immun/Virology
Type
Schools of Veterinary Medicine
DUNS #
193247145
City
East Lansing
State
MI
Country
United States
Zip Code
48824
Fyfe, John C; Hemker, Shelby L; Frampton, Alycia et al. (2018) Inherited selective cobalamin malabsorption in Komondor dogs associated with a CUBN splice site variant. BMC Vet Res 14:418
He, Qianchuan; Madsen, Mette; Kilkenney, Adam et al. (2005) Amnionless function is required for cubilin brush-border expression and intrinsic factor-cobalamin (vitamin B12) absorption in vivo. Blood 106:1447-53
Fyfe, John C; Madsen, Mette; Hojrup, Peter et al. (2004) The functional cobalamin (vitamin B12)-intrinsic factor receptor is a novel complex of cubilin and amnionless. Blood 103:1573-9
He, Qianchuan; Fyfe, John C; Schaffer, Alejandro A et al. (2003) Canine Imerslund-Grasbeck syndrome maps to a region orthologous to HSA14q. Mamm Genome 14:758-64