Project description:MicroRNAs (miRNAs) play an important role in the regulation of gene expression and are often dysregulated in disease. The recent development of the CRISPR-Cas9 gene-editing system, composed of the Cas9 nuclease in complex with a single guide RNA (sgRNA), allows researchers to direct DNA cleavage at a predetermined site and to conduct genome-scale knockout screens. To determine the functional role of miRNAs in cancer, we designed and constructed a library of 7,382 sgRNAs to target 85% of the 1,881 annotated human miRNA stem-loops. We then examined the role of miRNAs in HeLa cell fitness by monitoring the change in frequency of each sgRNA over time. We identified 44 pro-proliferative miRNAs from two replicate experiments, including miR-31, a known cervical cancer overexpressing miRNA that enhances HeLa cell proliferation. We also examined the role of miRNAs in NCI-N87 gastric cancer cells and identified 10 pro-fitness and 10 anti-fitness miRNAs. In both screens, many of the pro-fitness miRNAs identified are overexpressed in tumors cervical tumors for HeLa or gastric tumors for NCI-N87. In summary, we present a CRISPR miRNA-targeted screen which was able to identify both known and novel fitness-associated miRNAs in the HeLa and NCI-N87 cell lines.
Project description:We have sequenced miRNA libraries from human embryonic, neural and foetal mesenchymal stem cells. We report that the majority of miRNA genes encode mature isomers that vary in size by one or more bases at the 3’ and/or 5’ end of the miRNA. Northern blotting for individual miRNAs showed that the proportions of isomiRs expressed by a single miRNA gene often differ between cell and tissue types. IsomiRs were readily co-immunoprecipitated with Argonaute proteins in vivo and were active in luciferase assays, indicating that they are functional. Bioinformatics analysis predicts substantial differences in targeting between miRNAs with minor 5’ differences and in support of this we report that a 5’ isomiR-9-1 gained the ability to inhibit the expression of DNMT3B and NCAM2 but lost the ability to inhibit CDH1 in vitro. This result was confirmed by the use of isomiR-specific sponges. Our analysis of the miRGator database indicates that a small percentage of human miRNA genes express isomiRs as the dominant transcript in certain cell types and analysis of miRBase shows that 5’ isomiRs have replaced canonical miRNAs many times during evolution. This strongly indicates that isomiRs are of functional importance and have contributed to the evolution of miRNA genes
