A key regulatory gene in definitive erythropoiesis is the erythroid Kruppel-like factor (Eklf or Klf1). Klf1 knockout (KO) mice die in utero due to severe anemia, while residual circulating red blood cells retain their nuclei. Dnase2a is another critical gene in definitive erythropoiesis. Dnase2a KO mice are also affected by severe anemia and die in utero. DNase II-alpha is expressed in the central macrophage of erythroblastic islands (CMEIs) of murine fetal liver. Its main role is to digest the DNA of the extruded nuclei of red blood cells during maturation. Circulating erythrocytes retain their nuclei in Dnase2a KO mice. Here, we show that Klf1 is expressed in CMEIs and that it binds and activates the promoter of Dnase2a. We further show that Dnase2a is severely downregulated in the Klf1 KO fetal liver. We propose that this downregulation of Dnase2a in the CMEI contributes to the Klf1 KO phenotype by a non-cell-autonomous mechanism.

Sickle cell anemia (SCA) and thalassemia are among the most common genetic diseases worldwide. Current approaches to the development of murine models of SCA involve the elimination of functional murine alpha- and beta-globin genes and substitution with human alpha and betas transgenes. Recently, two groups have produced mice that exclusively express human HbS. The transgenic lines used in these studies were produced by coinjection of human alpha-, gamma-, and beta-globin constructs. Thus, all of the transgenes are integrated at a single chromosomal site. Studies in transgenic mice have demonstrated that the normal gene order and spatial organization of the members of the human beta-globin gene family are required for appropriate developmental and stage-restricted expression of the genes. As the cis-acting sequences that participate in activation and silencing of the gamma- and beta-globin genes are not fully defined, murine models that preserve the normal structure of the locus are likely to have significant advantages for validating future therapies for SCA. To produce a model of SCA that recapitulates not only the phenotype, but also the genotype of patients with SCA, we have generated mice that exclusively express HbS after transfer of a 240-kb betas yeast artificial chromosome. These mice have hemolytic anemia, 10% irreversibly sickled cells in their peripheral blood, reticulocytosis, and other phenotypic features of SCA.