MicroRNAs in hematopoietic development

MicroRNAs (miRNAs) are short non-coding RNAs involved in the posttranscriptional regulation of a wide range of biological processes. By binding to complementary sequences on target messenger RNAs, they trigger translational repression and degradation of the target, eventually resulting in reduced protein output. MiRNA-dependent regulation of protein translation is a very widespread and evolutionarily conserved mechanism of posttranscriptional control of gene expression. Accordingly, a high proportion of mammalian genes are likely to be regulated by miRNAs. In the hematopoietic system, both transcriptional and posttranscriptional regulation of gene expression ensure proper differentiation and function of stem cells, committed progenitors as well as mature cells. In recent years, miRNA expression profiling of various cell types in the hematopoietic system, as well as gene-targeting approaches to assess the function of individual miRNAs, revealed the importance of this type of regulation in the development of both innate and acquired immunity. We discuss the general role of miRNA biogenesis in the development of hematopoietic cells, as well as specific functions of individual miRNAs in stem cells as well as in mature immune cells.