Regulation of miRNA biogenesis and turnover in the immune system.

MicroRNAs (miRNAs) have emerged as important regulators of gene expression in diverse biological processes ranging from cell proliferation and survival to organ development and immunity. Here, we review mechanisms that regulate the expression of miRNAs themselves in the immune system. Like protein-coding genes, miRNAs can be regulated at the transcriptional level, downstream of signaling pathways and circuits that activate or inhibit transcription factors and chromatin remodeling. The resulting primary miRNAs are processed into active mature miRNAs through a series of biochemical steps, and miRNA abundance can be regulated at each step of this biogenesis pathway. Recent work has uncovered regulation of mature miRNA turnover in the immune system as well. A better understanding of these processes and their regulation by immunogenic stimuli is critical for integrating miRNAs into current models of gene expression networks that determine cell identity and immune function.