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Updated: Jul 15, 2026
Osmotic Avoidance in Caenorhabditis elegans: Synaptic Function of Two Genes, Orthologues of Human NRXN1 and NLGN1, as Candidates for Autism
Published on: December 11, 2009
Mechanistic insights and identification of two novel factors in the C. elegans NMD pathway
Dasa Longman1, Ronald H A Plasterk, Iain L Johnstone
1Medical Research Council Human Genetics Unit, Western General Hospital, Edinburgh EH4 2XU, Scotland, United Kingdom.
Abstract:
The nonsense-mediated mRNA decay (NMD) pathway selectively degrades mRNAs harboring premature termination codons (PTCs). Seven genes (smg-1-7, for suppressor with morphological effect on genitalia) that are essential for NMD were originally identified in the nematode Caenorhabditis elegans, and orthologs of these genes have been found in several species. Whereas in humans NMD is linked to splicing, PTC definition occurs independently of exon boundaries in Drosophila. Here, we have conducted an analysis of the cis-acting sequences and trans-acting factors that are required for NMD in C. elegans. We show that a PTC codon is defined independently of introns in C. elegans and, consequently, components of the exon junction complex (EJC) are dispensable for NMD. We also show a distance-dependent effect, whereby PTCs that are closer to the 3' end of the mRNA are less sensitive to NMD. We also provide evidence for the existence of previously unidentified components of the NMD pathway that, unlike known smg genes, are essential for viability in C. elegans. A genome-wide RNA interference (RNAi) screen resulted in the identification of two such novel NMD genes, which are essential for proper embryonic development, and as such represent a new class of essential NMD genes in C. elegans that we have termed smgl (for smg lethal). We show that the encoded proteins are conserved throughout evolution and are required for NMD in C. elegans and also in human cells.
Insights
Nonsense-mediated mRNA decay (NMD) in C. elegans degrades faulty mRNAs. New essential NMD genes, smgl, were discovered, crucial for development and conserved across species.
Area of Science:
- Molecular Biology
- Genetics
- Cell Biology
Background:
- The nonsense-mediated mRNA decay (NMD) pathway is a crucial cellular surveillance mechanism that eliminates aberrant messenger RNAs (mRNAs) containing premature termination codons (PTCs).
- Seven core NMD genes (smg-1-7) were initially identified in *Caenorhabditis elegans*, with orthologs found in diverse species, highlighting conserved NMD functions.
- NMD mechanisms vary across species; in humans, it is linked to splicing, while in *Drosophila*, PTC definition is independent of exon boundaries.
Purpose of the Study:
- To investigate the cis-acting sequences and trans-acting factors governing NMD in *C. elegans*.
- To identify novel components of the NMD pathway essential for *C. elegans* viability and development.
Main Methods:
- Analysis of cis-acting sequences and trans-acting factors involved in NMD in *C. elegans*.
- Genome-wide RNA interference (RNAi) screen to identify novel NMD genes.
- Comparative analysis of identified genes in *C. elegans* and human cells.
Main Results:
- PTC definition in *C. elegans* is independent of introns, rendering exon junction complex (EJC) components unnecessary for NMD.
- A distance-dependent effect on NMD sensitivity was observed, with 3'-proximal PTCs being less susceptible.
- Two novel NMD genes, termed *smgl* (smg lethal), essential for embryonic development and viability, were identified through an RNAi screen.
- The identified *smgl* proteins are evolutionarily conserved and play a role in NMD in both *C. elegans* and human cells.
Conclusions:
- NMD in *C. elegans* operates independently of splicing-associated factors like the EJC.
- Novel *smgl* genes represent a new class of essential NMD factors critical for *C. elegans* development.
- The conserved nature of *smgl* genes suggests fundamental roles in NMD across eukaryotes.
