Related Experiment Videos
mRNA surveillance mitigates genetic dominance in Caenorhabditis elegans
1Department of Genetics, University of Wisconsin, Madison 53706, USA.
Abstract:
Nonsense mutant mRNAs are unstable in all eucaryotes tested, a phenomenon termed nonsense-mediated mRNA decay (NMD) or mRNA surveillance. Functions of the seven smg genes are required for mRNA surveillance in Caenorhabditis elegans. In Smg(+) genetic backgrounds, nonsense-mutant mRNAs are unstable, while in Smg(-) backgrounds such mRNAs are stable. Previous work has demonstrated that the elevated level of nonsense-mutant mRNAs in Smg(-) animals can influence the phenotypic effects of heterozygous nonsense mutations. Certain nonsense alleles of a muscle myosin heavy chain gene are recessive in Smg(+) backgrounds but strongly dominant in Smg(-) backgrounds. Such alleles probably express disruptive myosin polypeptide fragments whose abundance is elevated in smg mutants due to elevation of mRNA levels. We report here that mutations in a variety of C. elegans genes are strongly dominant in Smg(-), but recessive or only weakly dominant in Smg(+) backgrounds. We isolated 32 dominant visible mutations in a Smg(-) genetic background and tested whether their dominance requires a functional NMD system. The dominance of 21 of these mutations is influenced by NMD. We demonstrate, furthermore, that in the case of myosin, the dominant-negative effects of nonsense alleles are likely to be due to expression of N-terminal nonsense-fragment polypeptides, not to mistranslation of the nonsense codons. mRNA surveillance, therefore, may mitigate potentially deleterious effects of many heterozygous germline and somatic nonsense or frame-shift mutations. We also provide evidence that smg-6, a gene previously identified as being required for NMD, performs essential function(s) in addition to its role in NMD.
Insights
Nonsense-mediated mRNA decay (NMD) normally degrades faulty mRNAs. Disabling NMD in C. elegans stabilizes these mRNAs, revealing hidden dominant mutations and impacting gene function.
Area of Science:
- Molecular Biology
- Genetics
- Cellular Biology
Background:
- Nonsense-mediated mRNA decay (NMD) is a conserved surveillance pathway that degrades aberrant mRNAs containing premature stop codons.
- The seven smg genes are essential for NMD function in the nematode Caenorhabditis elegans.
- Loss of NMD function (Smg(-) backgrounds) leads to the stabilization of nonsense-mutant mRNAs.
Purpose of the Study:
- To investigate how the stabilization of nonsense-mutant mRNAs in Smg(-) backgrounds affects the phenotypic expression of heterozygous mutations.
- To determine if the dominance of newly identified mutations in C. elegans is influenced by a functional NMD system.
- To elucidate the molecular mechanism underlying the dominant-negative effects of nonsense alleles, particularly in the context of mRNA surveillance.
Main Methods:
- Isolation and characterization of 32 dominant visible mutations in a Smg(-) C. elegans genetic background.
- Testing the dominance of these mutations in both Smg(-) and Smg(+) backgrounds to assess NMD dependency.
- Analysis of myosin heavy chain gene alleles to differentiate between polypeptide fragment expression and mistranslation as causes of dominant-negative effects.
Main Results:
- The dominance of 21 out of 32 isolated dominant mutations was found to be influenced by the NMD system.
- Nonsense alleles of the muscle myosin heavy chain gene exhibited strong dominance in Smg(-) backgrounds, but were recessive or weakly dominant in Smg(+) backgrounds.
- Evidence suggests that dominant-negative effects of myosin nonsense alleles are caused by the expression of N-terminal polypeptide fragments, not codon mistranslation.
Conclusions:
- mRNA surveillance (NMD) plays a crucial role in mitigating the potentially deleterious effects of heterozygous nonsense or frameshift mutations.
- The stability of nonsense-mutant mRNAs directly impacts the phenotypic manifestation of genetic mutations.
- The smg-6 gene, previously known for its role in NMD, possesses additional essential functions beyond mRNA surveillance.