MicroRNA-22 Promotes Megakaryocyte Differentiation through Repression of its Target, GFI1

Abstract

Precise control of microRNA expression contributes to development and the establishment of tissue identity, including in proper hematopoietic commitment and differentiation, while aberrant expression of various microRNAs has been implicated in malignant transformation. A small number of microRNAs are upregulated in megakaryocytes–among them is microRNA-22, whose dysregulation leads to various hematologic malignancies and disorders, but whose role in hematopoiesis is not yet well established. Here we show that the upregulation of microRNA-22 is a critical step in megakaryocyte differentiation. We have characterized hematopoiesis in microRNA-22 knockout animals and found that megakaryocyte differentiation is reduced. Further, megakaryocytic differentiation is disrupted in CRISPR/cas9-generated microRNA-22 knockout cell lines, while differentiation is promoted upon its overexpression, confirming that microRNA-22 is an essential mediator of this process. RNA sequencing reveals that microRNA-22 loss results in downregulation of megakaryocyte-associated genes. Mechanistically, we identify the repressive transcription factor, GFI1, as the direct target of microRNA-22, whose upregulation in the absence of microRNA-22 inhibits megakaryocyte differentiation. Repression of the Gfi1 transcript is incomplete in the megakaryocyte lineage in microRNA-22 knockout mice and Gfi1 is also aberrantly expressed upon forced megakaryocyte differentiation in explanted bone marrow from microRNA-22 knockout animals, which fail to be differentiated fully ex vivo. Further, knockdown of GFI1 using CRISPR-inhibition (CRISPRi) in the microRNA-22-null background restores megakaryopoiesis. This study identifies a positive role for microRNA22 in hematopoiesis, specifically in promoting megakaryocyte differentiation through repression of GFI1, a target antagonistic to this process.