title: A novel mutant allele of Ncx1: a single amino acid substitution leads to cardiac dysfunction.
abstract: The biological role and structure-function relationship of the Na(+)Ca(2+) exchanger NCX1 have been the subject of much investigation. Subtle mutagenesis to study the function of a protein seems only feasible in in vitro systems, but genetic forward screens have the potential to provide in vivo models to study single amino acid substitutions. In a genetic screen in mouse, we have isolated a mutant line carrying a novel mutant allele of the mouse Ncx1 gene. In this allele, a point mutation causes the substitution of a highly conserved asparagine residue (N874) with lysine. Accepted models for NCX1 structure propose that the affected amino acid is located in one of the reentrant membrane loops and experiments in vitro have identified N874 as critical for the ion transport function of NCX1. We found severe circulation defects and defective placentation in homozygous Ncx1(N87K4) mutant embryos, making the phenotype essentially indistinguishable from those of previously described null mutants. By ex vivo analysis, we demonstrated intrinsic functional abnormalities of cardiomyocytes. Western blot analysis and immunohistochemistry demonstrated normal levels and subcellular localization of the altered protein, ruling out the possibility that the abnormalities are a mere consequence of a major disturbance of protein structure. This study confirms and extends studies in vitro indicating the significance of amino acid N874 for the function of the NCX1 protein. It provides an in vivo model for this mutation and demonstrates the potential of forward genetic screens in a mammalian system.
authors.affiliation: Hubrecht Institute, KNAW and University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Carolien
authors.initials: C
authors.lastname: Wansleeben
authors.forename: Harma
authors.initials: H
authors.lastname: Feitsma
authors.forename: Leon
authors.initials: L
authors.lastname: Tertoolen
authors.forename: Carla
authors.initials: C
authors.lastname: Kroon
authors.forename: Victor
authors.initials: V
authors.lastname: Guryev
authors.forename: Edwin
authors.initials: E
authors.lastname: Cuppen
authors.forename: Frits
authors.initials: F
authors.lastname: Meijlink
mesh_terms: D000200:Action Potentials; D019943:Amino Acid Substitution; D000818:Animals; D002118:Calcium / Q000097:blood; D004622:Embryo, Mammalian / Q000378:metabolism; D005260:Female; D006330:Heart Defects, Congenital / Q000235:genetics*; D017136:Ion Transport; D051379:Mice; D008822:Mice, Transgenic; D009200:Myocardial Contraction; D032383:Myocytes, Cardiac / Q000473:pathology / Q000502:physiology*; D010641:Phenotype; D010929:Placentation; D011247:Pregnancy; D019831:Sodium-Calcium Exchanger / Q000737:chemistry / Q000235:genetics*; D013329:Structure-Activity Relationship
chemical_list: C499849:NCX1 protein, mouse; D019831:Sodium-Calcium Exchanger; D002118:Calcium