A novel ENU-generated truncation mutation lacking the spectrin-binding and C-terminal regulatory domains of Ank1 models severe hemolytic hereditary spherocytosis

Objective Hereditary spherocytosis (HS) is a heterogeneous group of spontaneously arising and inherited red blood cell disorders ranging from very mild subclinical cases to severe and life-threatening cases, with symptoms linked directly to the severity of the mutation at the molecular level. We investigated a novel mouse model in which the heterozygotes present with the diagnostic hallmarks of mild HS and surviving homozygotes phenocopy severe hemolytic HS. Materials and Methods We used N -ethyl- N -nitrosourea mutagenesis to generate random point mutations in the mouse genome and a dominant screen to identify mouse models of human hematopoietic disease. Gene mapping of the HS strain revealed a unique in-frame nonsense mutation arising from a single base transversion in exon 27 of Ank1 (strain designation: Ank1 E924X ). Employing conventional hematopoietic, pathological, biochemical, and cell biology assays, we characterized heterozygous and homozygous Ank1 E924X mice at the biochemical, cellular, and pathophysiological levels. Results Although Ank1 E924X/E924X red blood cell ghosts lack abundant full-length ankyrin-1 isoforms, N-terminal epitope ankyrin-1 antibodies reveal a band consistent with the theoretical size of a truncated mutant ankyrin-1. Using domain-specific antibodies, we further show that this protein lacks both a spectrin-binding domain and a C-terminal regulatory domain. Finally, using antisera that detect C-terminal residues of the products of alternative Ank1 transcripts, we find unique immunoreactive bands not observed in red blood cell ghosts from wild-type or Ank1 E924X heterozygous mice, including a band similar in size to full-length ankyrin-1. Conclusions The Ank1 E924X strain provides a novel tool to study Ank1 and model HS.