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Published on: February 13, 2012
mRNA surveillance of expressed pseudogenes in C. elegans
Quinn M Mitrovich1, Philip Anderson
1Department of Genetics, University of Wisconsin, Madison 53706, USA.
Abstract:
Messenger RNAs (mRNAs) that contain premature translation termination codons (PTCs) are targeted for rapid degradation in all eukaryotes tested. The mechanisms of nonsense-mediated mRNA decay (NMD) have been described in considerable detail, but the biological roles of NMD in wild-type organisms are poorly understood. mRNAs of wild-type organisms known to be degraded by NMD ("natural targets" of NMD) include by-products of regulated alternative splicing, out-of-frame mRNAs derived from unproductive gene rearrangements, cytoplasmic pre-mRNAs, endogenous retroviral and transposon RNAs, and mRNAs having upstream open reading frames or other unusual sequence features. NMD may function to eliminate aberrant PTC-containing mRNAs in order to protect cells from expression of potentially deleterious truncated proteins. Pseudogenes are nonfunctional genes or gene fragments that accumulate mutations through genetic drift. Such mutations will often introduce shifts of reading frame and/or PTCs, and mRNAs of expressed pseudogenes may thus be substrates of NMD. We demonstrate that mRNAs expressed from C. elegans pseudogenes are degraded by NMD and discuss possible implications for both mRNA surveillance and protein evolution. We describe an expressed pseudogene that encodes a small nucleolar RNA (snoRNA) within an intron and suggest this represents an evolutionary intermediate between snoRNA-encoding host genes that do or do not encode proteins.
Insights
Nonsense-mediated mRNA decay (NMD) degrades faulty transcripts. This study shows NMD also targets pseudogene messenger RNAs (mRNAs) in C. elegans, impacting gene regulation and evolution.
Area of Science:
- Molecular Biology
- Genetics
- Evolutionary Biology
Background:
- Nonsense-mediated mRNA decay (NMD) is a crucial surveillance pathway that degrades messenger RNAs (mRNAs) containing premature translation termination codons (PTCs).
- While NMD mechanisms are well-studied, its biological roles in normal cellular processes and gene regulation remain largely unclear.
- Pseudogenes, non-functional gene copies, often acquire mutations like PTCs and frameshifts, potentially making their transcripts targets for degradation.
Purpose of the Study:
- To investigate the role of NMD in the degradation of mRNAs transcribed from pseudogenes.
- To explore the implications of NMD activity on pseudogene expression and its potential contribution to protein evolution.
- To identify novel roles for NMD beyond the elimination of aberrant transcripts.
Main Methods:
- Analysis of mRNA decay pathways in C. elegans.
- Identification and characterization of expressed pseudogenes.
- Experimental validation of NMD targeting of pseudogene transcripts.
Main Results:
- Demonstrated that mRNAs expressed from C. elegans pseudogenes are actively degraded by the NMD pathway.
- Identified an expressed pseudogene encoding a small nucleolar RNA (snoRNA) within an intron.
- Provided evidence that pseudogene transcripts are natural substrates of mRNA surveillance.
Conclusions:
- NMD plays a significant role in regulating the expression of pseudogenes, preventing the production of potentially harmful truncated proteins.
- The degradation of pseudogene mRNAs by NMD may contribute to shaping the evolution of gene families and regulatory networks.
- The identified snoRNA-encoding pseudogene may represent an evolutionary intermediate in the development of novel gene functions.
