Cell-type specific sequencing of microRNAs from complex animal tissues.

MicroRNAs (miRNAs) play an essential role in the post-transcriptional regulation of animal development and physiology. However, in vivo studies aimed at linking miRNA function to the biology of distinct cell types within complex tissues remain challenging, partly because in vivo miRNA-profiling methods lack cellular resolution. We report microRNome by methylation-dependent sequencing (mime-seq), an in vivo enzymatic small-RNA-tagging approach that enables high-throughput sequencing of tissue- and cell-type-specific miRNAs in animals. The method combines cell-type-specific 3'-terminal 2'-O-methylation of animal miRNAs by a genetically encoded, plant-specific methyltransferase (HEN1), with chemoselective small-RNA cloning and high-throughput sequencing. We show that mime-seq uncovers the miRNomes of specific cells within Caenorhabditis elegans and Drosophila at unprecedented specificity and sensitivity, enabling miRNA profiling with single-cell resolution in whole animals. Mime-seq overcomes current challenges in cell-type-specific small-RNA profiling and provides novel entry points for understanding the function of miRNAs in spatially restricted physiological settings.

Neuron type-specific miRNA represses two broadly expressed genes to modulate an avoidance behavior in C. elegans.

Two broad gene classes are distinguished within multicellular organisms: cell type-specific genes, which confer particular cellular properties, and ubiquitous genes that support general cellular functions. However, certain so-called ubiquitous genes show functionally relevant cell type-specific repression. How such repression is achieved is poorly understood. MicroRNAs (miRNAs) are repressors, many of which are expressed with high cell type specificity. Here we show that mir-791, expressed exclusively in the CO2-sensing neurons in Caenorhabditis elegans, represses two otherwise broadly expressed genes. This repression is necessary for normal neuronal function and behavior of the animals toward CO2 miRNA-mediated repression of broadly transcribed genes is a previously unappreciated strategy for cellular specialization.