ABSTRACT
KLF1 regulates definitive erythropoiesis of red blood cells by facilitating transcription through high affinity binding to CACCC elements within its erythroid specific target genes including those encoding erythrocyte membrane skeleton (EMS) proteins. Deficiencies of EMS proteins in humans lead to the hemolytic anemia Hereditary Spherocytosis (HS) which includes a subpopulation with no known genetic defect. Here we report that a mutation, E339D, in the second zinc finger domain of KLF1 is responsible for HS in the mouse model Nan. The causative nature of this mutation was verified with an allelic test cross between Nan/+ and heterozygous Klf1(+/-) knockout mice. Homology modeling predicted Nan KLF1 binds CACCC elements more tightly, suggesting that Nan KLF1 is a competitive inhibitor of wild-type KLF1. This is the first association of a KLF1 mutation with a disease state in adult mammals and also presents the possibility of being another causative gene for HS in humans.
Subject(s)
Anemia, Hemolytic/pathology , Disease Models, Animal , Kruppel-Like Transcription Factors/genetics , Mutation/genetics , Spherocytosis, Hereditary/genetics , Anemia, Hemolytic/genetics , Animals , Humans , Mice , Mice, Inbred C57BL , Mice, Knockout , Zinc Fingers/geneticsABSTRACT
One of the most commonly inherited anemias in man is Hereditary Spherocytosis (HS) with an incidence of 1 in 2000 for persons of Northern European descent. Mouse models of HS include spontaneous inherited hemolytic anemias and those generated by gene targeting. The Neonatal anemia (Nan) mouse is a novel model of HS generated by N-ethyl-N-nitrosurea mutagenesis and suffers from a severe neonatal anemia. Adult Nan mice have a lifelong hemolytic anemia with decreased red blood cell numbers, hematocrit, and hemoglobin, but elevated zinc protoporphyrin levels. Blood smears taken from Nan mice show a hypochromic anemia characterized by poikilocytosis, anisocytosis and polychromasia. The Nan phenotype can be transferred by bone marrow transplantation indicating that the defect is intrinsic to bone marrow. The hemolytic anemia in adult Nan mice can be identified by osmotic fragility testing. Examination of the erythrocyte membrane skeleton proteins (EMS) reveals a global deficiency of these proteins with protein 4.1a being completely absent. The Nan locus maps to mouse Chromosome 8 and does not co-localize with any known EMS genes. The identification of the Nan gene will likely uncover a novel protein that contributes to the stability of the EMS and may identify a new mutation for HS.
