Neonatal expression of RNA-binding protein IGF2BP3 regulates the human fetal-adult megakaryocyte transition
Kamaleldin E. Elagib, … , Camelia Iancu-Rubin, Adam N. Goldfarb
Kamaleldin E. Elagib, … , Camelia Iancu-Rubin, Adam N. Goldfarb
Published May 8, 2017
Citation Information: J Clin Invest. 2017;127(6):2365-2377. https://doi.org/10.1172/JCI88936.
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Research Article Hematology

Neonatal expression of RNA-binding protein IGF2BP3 regulates the human fetal-adult megakaryocyte transition

Abstract

Hematopoietic transitions that accompany fetal development, such as erythroid globin chain switching, play important roles in normal physiology and disease development. In the megakaryocyte lineage, human fetal progenitors do not execute the adult morphogenesis program of enlargement, polyploidization, and proplatelet formation. Although these defects decline with gestational stage, they remain sufficiently severe at birth to predispose newborns to thrombocytopenia. These defects may also contribute to inferior platelet recovery after cord blood stem cell transplantation and may underlie inefficient platelet production by megakaryocytes derived from pluripotent stem cells. In this study, comparison of neonatal versus adult human progenitors has identified a blockade in the specialized positive transcription elongation factor b (P-TEFb) activation mechanism that is known to drive adult megakaryocyte morphogenesis. This blockade resulted from neonatal-specific expression of an oncofetal RNA-binding protein, IGF2BP3, which prevented the destabilization of the nuclear RNA 7SK, a process normally associated with adult megakaryocytic P-TEFb activation. Knockdown of IGF2BP3 sufficed to confer both phenotypic and molecular features of adult-type cells on neonatal megakaryocytes. Pharmacologic inhibition of IGF2BP3 expression via bromodomain and extraterminal domain (BET) inhibition also elicited adult features in neonatal megakaryocytes. These results identify IGF2BP3 as a human ontogenic master switch that restricts megakaryocyte development by modulating a lineage-specific P-TEFb activation mechanism, revealing potential strategies toward enhancing platelet production.

Authors

Kamaleldin E. Elagib, Chih-Huan Lu, Goar Mosoyan, Shadi Khalil, Ewelina Zasadzińska, Daniel R. Foltz, Peter Balogh, Alejandro A. Gru, Deborah A. Fuchs, Lisa M. Rimsza, Els Verhoeyen, Miriam Sansó, Robert P. Fisher, Camelia Iancu-Rubin, Adam N. Goldfarb

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Figure 4

Enforced IGF2BP3 expression in vivo perturbs adult murine megakaryopoiesis.

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Enforced IGF2BP3 expression in vivo perturbs adult murine megakaryopoies...
Adult murine marrow transduced with retrovirus expressing GFP ± IGF2BP3 was transplanted into lethally irradiated mice. At 6 weeks after transplant, recipients were treated with murine TPO (2 mg/d IP × 3 days). (A) Analysis of marrow megakaryocyte size (FSC) by flow cytometry, with gating on viable GFP+CD41+ cells. (B) Analysis of splenic megakaryocyte size (FSC) by flow cytometry, with gating on viable GFP+CD41+ cells. Graphs for A and B depict mean FSC ± SEM. n = 6/group. ***P < 0.005, t test. (C) Flow cytometry of marrow for CD41 and TER119 expression, with gating on viable GFP+ cells. Graphs represent mean ± SEM for percentages of CD41+TER119+ double-positive cells and percentages of all CD41+ cells. n = 6/group. *P < 0.05; ***P < 0.005, t test. See also Supplemental Figure 6.