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Haematologica 2021 Volume 106(2):464-473
Red Cell Biology & its Disorders
Hemoglobin switching in mice carrying the Klf1Nan variant
Anne Korporaal,1 Nynke Gillemans,1 Steven Heshusius,1,2 Ileana Cantú,1 Emile van den Akker,2 Thamar B. van Dijk,1 Marieke von Lindern2
and Sjaak Philipsen1
1Erasmus MC Department of Cell Biology, Rotterdam and 2Sanquin Research Department of Hematopoiesis, Amsterdam and Landsteiner Laboratory, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands
ABSTRACT
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 hemoglo- bin. 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 ane- mia, accompanied by persistently high levels of embryonic and fetal hemo- globin. The mouse Nan strain carries a variant in the orthologous residue, KLF1 p.E339D. Klf1Nan causes dominant hemolytic anemia with many simi- larities to CDA-IV. Here we investigated the impact of Klf1Nan on the developmental expression patterns of the endogenous α-like and β-like glo- bins, 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 Klf1wt/Nan embryos. This is reflected in globin expression patterns measured between embryon- ic day 12.5 (E12.5) and E14.5. Cultured Klf1wt/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 Klf1wt/Nan embryos. After E14.5, expression of the embryonic/fetal globin genes is silenced rapidly. In adult Klf1wt/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, high- lighting the necessity to characterize KLF1 variant-specific phenotypes of patients in detail.
Introduction
KLF1 is an erythroid-specific transcription factor with diverse and essential roles during terminal erythroid differentiation.1 Cloned from mouse erythroleukemia cells it was initially called erythroid Krüppel-like factor (EKLF) in honor of its ery- throid-specific expression and DNA-binding domain.2 This domain is composed of three Cys2-His2 zinc fingers similar to those found in the Drosophila Krüppel tran- scription factor. KLF1 is the founding member of the KLF branch of the 27-strong SP/KLF family.3 Despite the fact that other SP/KLF factors such as SP1, SP3, KLF2, KLF3 and KLF8 are abundantly expressed in erythroid cells,4,5 gene inactivation in mice demonstrated that KLF1 is essential for definitive erythropoiesis.6,7 Specifically, activation of β-globin expression was strongly impaired leading to a severe β-thalassemia phenotype. Restoring globin chain imbalance with a human γ-globin transgene failed to rescue the embryonic lethality of KLF1 deficiency,8 indicating that other KLF1 target genes contribute to the erythroid defects. This was confirmed by genome-wide expression analyses which established that KLF1 is involved in virtually every aspect of terminal erythroid differentiation.9-12 In humans, the first KLF1 variants reported were identified as the molecular basis of the rare blood type In(Lu).13 In all cases one normal KLF1 allele was present show- ing that, similar to Klf1wt/ko mice,6,7 this is sufficient to sustain erythropoiesis. These
Correspondence:
SJAAK PHILIPSEN
j.philipsen@erasmusmc.nl
Received: October 4, 2019. Accepted: January 23, 2020. Pre-published: May 28, 2020.
https://doi.org/10.3324/haematol.2019.239830
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