MicroRNAs: Key players of normal and malignant myelopoiesis

Purpose of review: Recent data show that microRNAs play critical roles in the regulation of the developmental process of hematopoietic stem and progenitor cells toward mature myeloid cells. The main focus of the article is the function of some evolutionary conserved microRNAs that are abundantly expressed and tightly regulated during myelopoiesis. Recent findings: Global microRNA depletion studies in hematopoietic stem cells have shown the importance of microRNA-controlled pathways for hematopoiesis. Recent insights from genetic mouse models and overexpression or deletion of microRNAs in developmental cell intermediates demonstrate strong evidence for evolutionary conserved microRNA-regulated pathways involved in tight control of cellular processes such as proliferation, differentiation and apoptosis at different stages of blood cell development. It is becoming evident that the myeloid transcription factor PU.1 regulates the expression of critical microRNAs including miR-17 -1/492 and miR-146a during myelopoiesis. Furthermore, there is evidence for the contribution of aberrant miR-125 activities in hematopoietic disorders including myeloid leukemia. Summary: Despite the large number of articles describing differential microRNA expression during hematopoiesis, microRNA functions and their downstream pathways in myeloid lineage decisions and leukemia are only recently emerging. Here we discuss new findings concerning PU.1-controlled microRNAs and miR-125-regulated networks in normal and malignant myelopoiesis.

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