Cdan1 is essential for primitive erythropoiesis

Congenital dyserythropoietic anemia type I (CDA I), is an autosomal recessive disease with macrocytic anemia in which erythroid precursors in the bone marrow exhibit pathognomonic abnormalities including spongy heterochromatin. The disease is mainly caused by mutations in CDAN1. No patients with homozygous LOF mutations have been described, and mouse null mutants die during early embryogenesis prior to the initiation of erythropoiesis. To investigate the role of Codanin-1 in erythropoiesis, we crossed mice carrying Cdan1 floxed allele (Cdanfl/fl) with mice expressing Cre-recombinase under regulation of the erythropoietin receptor promoter (ErGFPcre). The resulting Cdan^ΔEry transgenic embryos died at mid-gestation (E12.5-E13.5) from severe anemia, suggesting that Cdan1 is necessary for primitive erythroblasts survival.

Spongy or "Swiss-cheese" like heterochromatin is considered the pathognomonic feature of CDAI. TEM analysis revealed that Cdan^ΔEry erythroblasts (E9.5) exhibit this heterochromatin abnormality. The morphology of Cdan^ΔEry primitive erythroblasts demonstrated progressive development of dyserythropoiesis. Flow cytometry studies demonstrated that Cdan^ΔEry erythroid progenitors do not undergo the semi-synchronous maturation characteristic of primitive erythroblasts. Gene expression studies aimed to evaluate the effect of Cdan1 depletion on erythropoiesis revealed dysregulated globin expression. We also found increased expression of Gata2, Pu.1, and Runx1, which are known to inhibit terminal erythroid differentiation. Consistent with this data, our zebrafish model showed increased gata2 expression upon cdan1 knockdown.

In summary, we demonstrated for the first time that Cdan1 is required for primitive erythropoiesis, while providing two experimental models for studying the role of Codanin-1 in erythropoiesis and in the pathogenesis of CDA type I.