Analysis of 3' End Modifications in microRNAs by High-Throughput Sequencing.

MicroRNAs are ~22 nt small, non-coding RNAs that direct posttranscriptional silencing of gene expression to regulate animal development, physiology, and disease. An emerging mechanism that controls the biogenesis of microRNAs is the addition of non-templated nucleotides, predominantly uridine, to the 3' end of precursor-microRNAs, in a process that is commonly referred to as tailing. Here, we describe methods that enable the systematic characterization of tailing events in mature microRNAs and their precursors. We report protocols for untargeted and targeted cDNA library preparation procedures, as exemplified in the context of the model organism Drosophila melanogaster and focusing on precursor-microRNAs. We also refer to a dedicated computational framework for the subsequent analysis of untemplated nucleotide additions in cDNA libraries. The described methods for the systematic characterization of posttranscriptional modifications in gene regulatory small RNAs and their precursors will be instrumental in clarifying regulatory concepts that control posttranscriptional gene silencing.