Genomic non-redundancy of the mir-183/96/182 cluster and its requirement for hair cell maintenance

microRNAs are important regulators of gene expression. In the retina, the mir-183/96/182 cluster is of particular interest due to its robust expression and studies in which loss of the cluster caused photoreceptor degeneration. However, it is unclear which of the three miRNAs in the cluster are ultimately required in photoreceptors, whether each may have independent, contributory roles, or whether a single miRNA from the cluster compensates for the loss of another. These are important questions that will not only help us to understand the role of these particular miRNAs in the retina, but will deepen our understanding of how clustered microRNAs evolve and operate. To that end, we have developed a complete panel of single, double, and triple mir-183/96/182 mutant zebrafish. While the retinas of all mutant animals were normal, the triple mutants exhibited acute hair cell degeneration which corresponded with impaired swimming and death at a young age. By measuring the penetrance of this phenotype in each mutant line, we determine which of the three miRNAs in the cluster are necessary and/or sufficient to ensure normal hair cell development and function.