The roles of microRNAs in mouse development.

Hundreds of microRNAs (miRNAs) are expressed in distinct spatial and temporal patterns during embryonic and postnatal mouse development. The loss of all miRNAs through the deletion of critical miRNA biogenesis factors results in early lethality. The function of each miRNA stems from their cumulative negative regulation of multiple mRNA targets expressed in a particular cell type. During development, miRNAs often coordinate the timing and direction of cell fate transitions. In adults, miRNAs frequently contribute to organismal fitness through homeostatic roles in physiology. Here, we review how the recent dissection of miRNA-knockout phenotypes in mice as well as advances related to their targets, dosage, and interactions have collectively informed our understanding of the roles of miRNAs in mammalian development and adaptive responses. MicroRNAs (miRNA) exert essential functions in mammalian development and physiology. The authors review recent insights from the phenotypic analysis of miRNA knockouts in mice that emphasize roles for these non-coding RNAs at different developmental stages and in adults, and illustrate the importance of functional miRNA targets, miRNA dosage, miRNA interactions and cellular context.