MicroRNAs and hematopoietic cell development.

Hematopoiesis is a dynamic and highly complex developmental process that gives rise to a multitude of the cell types that circulate in the blood of multicellular organisms. These cells provide tissues with oxygen, guard against infection, prevent bleeding by clotting, and mediate inflammatory reactions. Because the hematopoietic system plays such a central role in human diseases such as infections, cancer, autoimmunity, and anemia, it has been intensely studied for more than a century. This scrutiny has helped to shape many of the developmental paradigms that exist today and has identified specific protein factors that serve as master regulators of blood cell lineage specification. Despite this progress, many aspects of blood cell development remain obscure, suggesting that novel layers of regulation must exist. Consequently, the emergence of regulatory noncoding RNAs, such as the microRNAs (miRNAs), is beginning to provide new insights into the molecular control networks underlying hematopoiesis and diseases that stem from aberrations in this process. This review will discuss how miRNAs fit into our current understanding of hematopoietic development in mammals and how breakdowns in these pathways can trigger disease. Copyright Â