Hemoglobin switching in mice carrying the Klf1Nan variant

Haploinsufficiency for transcription factor KLF1 causes a variety of human erythroid phenotypes, such as the In(Lu) blood type, increased HbA2 levels, and hereditary persistence of fetal hemoglobin. Severe dominant congenital dyserythropoietic anemia IV (CDA-IV) (OMIM 613673) is associated with the KLF1 p.E325K variant. CDA-IV patients display ineffective erythropoiesis and hemolysis resulting in anemia, accompanied by persistently high levels of embryonic and fetal hemoglobin. The mouse Nan strain carries a variant in the orthologous residue, KLF1 p.E339D. Klf1(Nan) causes dominant hemolytic anemia with many similarities to CDA-IV. Here we investigated the impact of Klf1(Nan) on the developmental expression patterns of the endogenous α-like and β-like globins, and the human β-like globins carried on a HBB locus transgene. We observe that the switch from primitive, yolk sac-derived, erythropoiesis to definitive, fetal liver-derived, erythropoiesis is delayed in Klf1(wt/Nan) embryos. This is reflected in globin expression patterns measured between embryonic day 12.5 (E12.5) and E14.5. Cultured Klf1(wt/Nan) E12.5 fetal liver cells display growth- and differentiation defects. These defects likely contribute to the delayed appearance of definitive erythrocytes in the circulation of Klf1(wt/Nan) embryos. After E14.5, expression of the embryonic/fetal globin genes is silenced rapidly. In adult Klf1(wt/Nan) animals, silencing of the embryonic/fetal globin genes is impeded, but only minute amounts are expressed. Thus, in contrast to human KLF1 p.E325K, mouse KLF1 p.E339D does not lead to persistent high levels of embryonic/fetal globins. Our results support the notion that KLF1 affects gene expression in a variant-specific manner, highlighting the necessity to characterize KLF1 variant-specific phenotypes of patients in detail.