RESUMO
Studies of mouse models of anemia have long provided fundamental insights into red blood cell formation and function. Here we show that the semidominant mouse mutation Nan ("neonatal anemia") carries a single amino acid change (E339D) within the second zinc finger of the erythroid Krüppel-like factor (EKLF), a critical erythroid regulatory transcription factor. The mutation alters the DNA-binding specificity of EKLF so that it no longer binds promoters of a subset of its DNA targets. Remarkably, even when mutant Nan and wild-type EKLF alleles are expressed at equivalent levels, the mutant form selectively interferes with expression of EKLF target genes whose promoter elements it no longer binds. This interference yields a distorted genetic output and selective protein deficiencies that differ from those seen in EKLF-heterozygous and EKLF-null red blood cells and presents a unique and unexpected mechanism of inherited disease.
Assuntos
Anemia/genética , Fatores de Transcrição Kruppel-Like/genética , Substituição de Aminoácidos , Anemia/metabolismo , Animais , Sequência de Bases , Sítios de Ligação/genética , Mapeamento Cromossômico , DNA/genética , DNA/metabolismo , Modelos Animais de Doenças , Eritrócitos/metabolismo , Feminino , Expressão Gênica , Genes Reporter , Hemoglobinas/genética , Heterozigoto , Humanos , Células K562 , Fatores de Transcrição Kruppel-Like/química , Fatores de Transcrição Kruppel-Like/metabolismo , Masculino , Camundongos , Camundongos Endogâmicos C3H , Camundongos Mutantes , Modelos Moleculares , Proteínas Mutantes/química , Proteínas Mutantes/genética , Proteínas Mutantes/metabolismo , Mutação de Sentido Incorreto , Fenótipo , Gravidez , Regiões Promotoras Genéticas , Ativação Transcricional , Dedos de Zinco/genéticaRESUMO
Defects in red blood cell (RBC) membrane skeleton components cause hereditary spherocytosis (HS). Clinically, HS varies significantly even among individuals with identical gene defects, illustrating the profound effects of genetic background on disease severity. We exploited a new spontaneous mouse model, wan, which arose on the inbred C3H/HeJ strain, to identify quantitative trait loci (QTL) that modify the HS phenotype. Homozygous wan mice have severe HS due to a complete deficiency of erythroid band 3. A QTL analysis of RBC count, hemoglobin, hematocrit, mean corpuscular volume (MCV), and mean corpuscular hemoglobin content (MCHC) was performed in wan/wan mice from an F2 intercross between C3H/HeJ(+/wan) and CAST/Ei(+/+) F1 hybrids. Hematologic and survival data from C3H, CAST/Ei F2 wan homozygotes support the hypothesis that genetic modifiers significantly influence the band-3 null HS phenotype. Significant QTL were identified for the MCV trait only, suggesting that RBC membrane characteristics are a target for modifier gene action. The most significant quantitative trait locus, Hsm1 (hereditary spherocytosis modifier 1), localizes to mouse Chromosome 12 and is dominant. The peak LOD score was obtained with a marker for Spnb1 encoding erythroid beta-spectrin, an obvious candidate gene.