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.