Project description:Ribosome profiling has revealed pervasive but largely uncharacterized translation outside of canonical coding sequences (CDSs). Here, we exploit a systematic CRISPR-based screening strategy to identify hundreds of non-canonical CDSs that are essential for cellular growth and whose disruption elicit specific, robust transcriptomic and phenotypic changes in human cells. Functional characterization of the encoded microproteins reveals distinct cellular localizations, specific protein binding partners, and hundreds that are presented by the HLA system. Interestingly, we find multiple microproteins encoded in upstream open reading frames, which form stable complexes with the main, canonical protein encoded on the same mRNA, thus revealing the diverse use of functional bicistronic operons in mammals. Together, our results point to a family of functional human microproteins that play critical and diverse cellular roles.
Project description:We present a genome-wide assessment of small open reading frames (smORF) translation by ribosomal profiling of polysomal fractions in Drosophila S2 cell. In this way, mRNAs bound by multiple ribosomes and hence actively translated can be isolated and distinguished from mRNAs bound by sporadic, putatively non-productive single ribosomes or ribosomal subunits. Ribosomal profiling of large and small polysomal fractions in Drosophila S2 cells to assess translation of smORFs
Project description:We present a genome-wide assessment of small open reading frames (smORF) translation by ribosomal profiling of polysomal fractions in Drosophila S2 cell. In this way, mRNAs bound by multiple ribosomes and hence actively translated can be isolated and distinguished from mRNAs bound by sporadic, putatively non-productive single ribosomes or ribosomal subunits.
Project description:Protein-coding regions of the genome continue to expand beyond canonical annotations and remain incompletely understood. Despite recent reports demonstrating important cellular functions played by micropeptides from unannotated open reading frames (ORFs), there exists no systematic method to fully uncover the prevalence of functional ORFs and their encoded peptides. Here, using ribosome profiling and mass spectrometry based proteomics, we reveal pervasive translation of ORFs previously annotated as non-coding, including those encoded on long non-coding RNAs (lncRNA ORFs) and upstream regions of protein-coding messages (uORFs). Cross-validation of novel ORFs in six different cell lines via HLA peptidomics confirm their allotype-specific MHC receptor presentation and their engagement with the endogenous HLA processing machinery. We further developed systematic CRISPR-based screens to show that hundreds of these ORFs are essential for cellular growth and encode stable, functional peptides that play diverse roles in cells. By tagging with a split-GFP system, we show that many of the peptides have specific cellular localization patterns and form functional protein complexes. We uncovered uORFs encoding stable peptides that interact with the downstream protein encoded on the same mRNA, suggesting possible regulatory or feedback roles from the bicistronic message in addition to the previously assumed role of uORFs in translational repression. Our results uncover functional micropeptides encoded in the human genome with essential roles in diverse biological processes.
Project description:Open reading frames (ORFs) are the genomic DNA sequences that have the potential to be translated. Genome annotation pipelines dismiss translation products of small ORFs (smORFs) of less than 100 codons (<300 nucleotides) as being unlikely to have a biological function. In this study, we systematically characterized smORFs in mouse B and T cells under different conditions and predicted a total of 5744 unique actively translated smORFs. We then extended our analysis to ORFs of 101-200 codons in length and predicted 945 of such longer translation products. Additionally, our results have suggested the existence of candidate secreted micropeptides. Furthermore, verifying their existence and identifying their functions will be essential and potentially lead to useful applications.
Project description:Ribosome profiling analyses showed thousands of translated open reading frames in a cell encoding noncanonical peptides. To examine their functional roles, we stably overexpressed two noncanonical peptides (uSLC35A4 and iPGRMC1) in MCF-7 cells. And then we performed RNA-seq to examine differential gene expression upon gene overexpression.