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Gene expression data from E14.5 Pogz-WT and Pogz-KO fetal livers.

ABSTRACT: Fetal and adult β-globin gene expression is tightly regulated during human development. Fetal globin genes are transcriptionally silenced during embryogenesis through the process of hemoglobin switching. Efforts to understand the transcriptional mechanism(s) behind fetal globin silencing have led to novel strategies to derepress fetal globin expression in the adult, which could alleviate symptoms in hereditary b-globin disorders including sickle cell disease (SCD) and β-thalassemia. We identified a novel zinc finger protein, pogo transposable element with zinc finger domain (Pogz), expressed in mouse and human hematopoietic stem and progenitor cells, which represses embryonic b-like globin gene expression in mice. Ablation of Pogz expression in adult hematopoietic cells in vivo results in persistence of embryonic b-like globin expression without significantly affecting erythroid development or mouse survival. Elevated embryonic β-like globin expression correlates with reduced expression of Bcl11a, a known repressor of embryonic β-like globin expression, in Pogz-/- fetal liver cells. Pogz binds to the Bcl11a promoter, and, to erythroid specific intragenic regulatory regions. Importantly, Pogz+/- mice develop normally, but show elevated embryonic b-like globin expression in peripheral blood cells, demonstrating that reducing Pogz levels results in persistence of embryonic b-like globin expression. Finally, knockdown of POGZ in primary human CD34+ hematopoietic stem and progenitor cell derived erythroblasts, reduces BCL11A expression and increases fetal hemoglobin expression. These findings are significant since new therapeutic targets and strategies are needed to treat the increasing global burden of b-globin disorders.

ORGANISM(S): Mus musculus

PROVIDER: GSE113503 | GEO | 2018/06/21

REPOSITORIES: GEO

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Project description:Basak A, Munschauer M, Lareau CA, Montbleau KE, Ulirsch JC, Hartigan CR, Schenone M, Lian J, Wang Y, Huang Y, Wu X, Gehrke L, Rice CM, An X, Christou HA, Mohandas N, Carr SA, Orkin SH, Chen JJ, Lander ES, and Sankaran VG. Increased production of the beta-like gamma-globin genes that form fetal hemoglobin can ameliorate the severity of sickle cell disease and beta-thalassemia, the major hemoglobin disorders. BCL11A is a key repressor of the gamma-globin genes and is expressed in a developmental stage-specific manner to regulate the physiologic fetal-to-adult hemoglobin switch. Despite extensive studies, the upstream mechanisms underlying the developmental expression of BCL11A and hemoglobin switching in humans have remained mysterious. Here we show that BCL11A is regulated at the level of mRNA translation during human hematopoietic development. While BCL11A mRNA is comparably expressed at all developmental stages in erythroid cells, robust protein expression only occurs in adult erythroid cells. Importantly, at the earlier stages of development, the observed reduction in protein expression is attributable to decreased synthesis and not increased degradation of BCL11A. While BCL11A protein is not well synthesized at these earlier stages of development, its mRNA curiously continues to be associated with ribosomes. Through unbiased proteomic analyses in erythroid cells, we demonstrate that the RNA-binding protein LIN28B, which is developmentally expressed in a reciprocal pattern to BCL11A, directly interacts with ribosomes. We show that the observed suppression of BCL11A protein translation is mediated by LIN28B through a direct interaction with BCL11A mRNA and independent of its role in let-7 microRNA biogenesis. Finally, we show that BCL11A is the major functional target in LIN28B-mediated fetal hemoglobin induction. Our results reveal a previously unappreciated regulatory mechanism underlying human hemoglobin switching and illuminate opportunities for developing improved treatments for sickle cell disease and beta-thalassemia.

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Gene expression data from E14.5 Pogz-WT and Pogz-KO fetal livers.

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