MicroRNAs and haematology: small molecules, big function.

MicroRNAs are a recently discovered class of small ( approximately 22nt) endogenously expressed translational-repressor RNAs that play key roles in many cellular pathways and whose aberrant expression appears to be a common feature of malignancy. MicroRNAs are expressed in specific haematological cell types and play important regulatory roles in early haematopoietic differentiation, erythropoiesis, granulocytosis, megakaryocytosis and lymphoid development. Additionally, there is an emerging body of research to suggest that microRNAs play an important role in the pathology of haematological malignancies. MicroRNAs have been found to act as both tumour suppressor molecules [e.g. MIRN15A (miR-15a), MIRN16-1 (miR-16-1)] in leukaemias and have oncogenic properties [e.g. MIRN155 (miR-155) and MIRN17-92 (miR-17-miR-92) cluster] in lymphomas. This review discusses the rapidly accumulating research that points to the major role microRNAs play in both haematopoiesis and haematological malignancy.