A GFP-based reporter system to monitor nonsense-mediated mRNA decay
Alexandra Paillusson1, Nadine Hirschi, Claudio Vallan
1Institute of Cell Biology, University of Bern CH-3012 Bern, Switzerland.
Abstract:
Aberrant mRNAs whose open reading frame (ORF) is truncated by the presence of a premature translation-termination codon (PTC) are recognized and degraded in eukaryotic cells by a process called nonsense-mediated mRNA decay (NMD). Here, we report the development of a reporter system that allows monitoring of NMD in mammalian cells by measuring the fluorescence of green fluorescent protein (GFP). The NMD reporter gene consists of a T-cell receptor-beta minigene construct, in which the GFP-ORF was inserted such that the stop codon of GFP is recognized as PTC. The reporter mRNA is therefore subjected to NMD, resulting in a low steady-state mRNA level, an accordingly low protein level and hence a very low green fluorescence in normal, NMD-competent cells that express this reporter gene. We show that the inactivation of NMD by RNAi-mediated knockdown of the essential NMD factor hUpf1 or hSmg6 increases the NMD reporter mRNA level, resulting in a proportional increase of the green fluorescence that can be detected by flow cytometry, spectrofluorometry and fluorescence microscopy. With these properties, our GFP-based NMD reporter system could be used for large-scale screenings to identify NMD-inhibiting drugs or NMD-deficient mutant cells.
Insights
Researchers developed a novel reporter system to monitor nonsense-mediated mRNA decay (NMD) in mammalian cells using green fluorescent protein (GFP). This system enables efficient screening for NMD inhibitors and deficient cells.
Area of Science:
- Molecular Biology
- Cell Biology
- Genetics
Background:
- Nonsense-mediated mRNA decay (NMD) is a crucial surveillance pathway in eukaryotic cells.
- NMD degrades aberrant mRNAs containing premature translation-termination codons (PTCs).
- Monitoring NMD activity is essential for understanding gene regulation and disease mechanisms.
Purpose of the Study:
- To develop a novel, quantifiable reporter system for monitoring NMD in mammalian cells.
- To validate the reporter system's responsiveness to NMD modulation.
- To establish a tool for high-throughput screening of NMD-modulating compounds or cell lines.
Main Methods:
- Constructed a reporter gene by inserting green fluorescent protein (GFP) into a T-cell receptor-beta minigene, ensuring GFP's stop codon functions as a PTC.
- Expressed the reporter in mammalian cells and measured GFP fluorescence.
- Inactivated key NMD factors (hUpf1, hSmg6) using RNA interference (RNAi) to modulate NMD activity.
- Quantified reporter mRNA levels and GFP fluorescence using flow cytometry, spectrofluorometry, and fluorescence microscopy.
Main Results:
- The reporter mRNA is efficiently degraded by NMD in NMD-competent cells, leading to low GFP expression.
- Knockdown of hUpf1 or hSmg6 significantly increased reporter mRNA levels and GFP fluorescence.
- The GFP fluorescence signal directly correlated with NMD activity levels.
- The reporter system demonstrated sensitivity and reliability in detecting changes in NMD activity.
Conclusions:
- A robust and sensitive GFP-based reporter system for monitoring NMD in mammalian cells has been successfully developed.
- This reporter system allows for real-time, quantitative assessment of NMD activity.
- The system is suitable for large-scale screening to identify potential NMD-inhibiting drugs or to characterize NMD-deficient cells.
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