The Yin and Yang of microRNAs: leukemia and immunity

Summary Yin and Yang are two complementary forces that together describe the nature of real‐world elements. Yin is the dark side; Yang is the light side. We describe microRNAs having both Yin and Yang characteristics because they can contribute to normal function (Yang) but also to autoimmunity, myeloproliferation, and cancer (Yin). We have been working on a number of microRNAs that have these dual characteristics and here we focus on two, miR‐125b and miR‐146a. We have concentrated on these two RNAs because we have very extensive knowledge of them, much of it from our laboratory, and also because they provide a strong contrast: the effects of overexpression of miR‐125b are rapid, suggesting that it acts directly, whereas the effects of miR‐146a are slow to develop, suggesting that they arise from chronic alterations in cellular behavior.