A Novel ENU-Induced Intronic Mutation of Ank1 Causing Quantitative Defect of Ankyrin-1 Models Hemolytic Hereditary Spherocytosis in Mouse

Abstract 989

The ability of red blood cells (RBCs) to maintain the surface area and deformability is vital for their survival. The maintenance of membrane surface is dependent upon the strong cohesion between the lipid bilayer and the skeletal network, achieved by vertical linkages between transmembrane proteins and spectrin tetramers. Mutations causing functional deficiencies in these proteins have been identified in various hemolytic anemias. Here we reported a mild hereditary spherocytosis (HS) and hemolytic anemia phenotype in mouse, named hema6, induced by N-ethyl-N-nitrosourea (ENU) mutagenesis. Hema6 phenotype is transmitted as a semidominant trait as heterozygous mice are less severely affected than homozygotes. The causal mutation was traced to a single nucleotide transition in the deep intronic region of intron 13 of gene Ank1, encoding the anchorage protein ankyrin-1 in RBC. In vitro minigene assay revealed two abnormally spliced transcripts in addition to wild-type mRNA. The wild-type Ank1 transcript was detected in the homozygous mutant mouse with 30% reduction in expression level compared to that in wild type mouse. The aberrant transcripts presumably encoded a 509 amino acids protein, which lacks beta-spectrin binding domain and C-terminal regulatory region. The truncated protein was not detected by western blotting using currently available antibodies against full-length ankyrin-1 in homozygous hema6 erythrocyte ghosts, whereas the wild-type Ankyrin-1 are present with reduced quantity. Employing biochemical and cell biology assays, we characterized the mechanism by which Ank1^hema6 mutation causes hemolytic hereditary spherocytosis in mouse. Hema6 strain provides a novel tool to study ankyrin-1 and its pathogenesis role in HS.