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Published on: September 25, 2013
Analysis of dominant-negative mutations of the Caenorhabditis elegans let-60 ras gene
1Howard Hughes Medical Institute, Division of Biology, California Institute of Technology, Pasadena 91125.
Abstract:
The let-60 gene of Caenorhabditis elegans controls the choice between vulval and hypodermal differentiation in response to an inductive signal from the gonad. let-60 encodes a ras protein that acts downstream of the let-23 receptor tyrosine kinase in a signal transduction pathway. Dominant-negative mutations of let-60 [let-60(dn)] cause a reduction of the gene activity in let-60(dn)/+ heterozygotes and a vulva-less mutant phenotype. We have found that nine let-60(dn) mutations cause replacements of conserved residues. Four are in two novel positions; others are in positions known previously to cause dominant-negative mutations in mammalian cells. The locations of these lesions suggest that they disrupt the ability of the ras protein to bind guanine nucleotides. Four let-60(dn) mutant genes were introduced into wild-type animals in the form of extrachromosomal arrays and were found to generate three dominant phenotypes--lethality, vulva-less, or multivulva--depending on gene dose and alleles. The dominant lethality caused by high-dose transgenic let-60(dn) genes suggests a toxic effect of these mutant genes in early development. The dominant-negative effects of these mutations in heterozygotes are likely to be caused by competition between let-60(dn) and let-60(+) protein for a positive regulator. All let-60(dn) mutations interfere with let-60(+) activity, but some alleles have partial constitutive activity, suggesting that the ability to interact with the activator is separable from the ability to exert a physiological effect (stimulation of vulval differentiation). These dn mutations might be useful for interfering with ras-mediated signal transduction pathways in other multicellular organisms.
Insights
Dominant-negative mutations in the let-60 gene, encoding a ras protein, disrupt Caenorhabditis elegans development. These mutations interfere with ras signaling, affecting cell differentiation and causing developmental defects like lethality or altered vulva formation.
Area of Science:
- Developmental Biology
- Molecular Genetics
- Cell Signaling
Background:
- The let-60 gene in C. elegans encodes a ras protein crucial for signal transduction pathways.
- It acts downstream of the let-23 receptor tyrosine kinase, mediating cell fate decisions.
- Dominant-negative let-60 mutations [let-60(dn)] impair gene activity, leading to a vulva-less phenotype.
Purpose of the Study:
- To characterize the molecular basis of dominant-negative let-60 mutations.
- To investigate the effects of let-60(dn) mutations on C. elegans development in a dose-dependent manner.
- To explore the potential utility of these mutations in studying ras-mediated signaling.
Main Methods:
- Analysis of nine let-60(dn) mutations, identifying conserved residue replacements.
- Introduction of four let-60(dn) mutant genes into wild-type animals via extrachromosomal arrays.
- Observation of resulting phenotypes including lethality, vulva-less, and multivulva.
Main Results:
- Nine let-60(dn) mutations identified, with four affecting novel positions and five known dominant-negative positions.
- Mutations likely disrupt guanine nucleotide binding in the ras protein.
- Transgenic expression of let-60(dn) resulted in dose-dependent phenotypes: lethality, vulva-less, or multivulva.
- Dominant-negative effects in heterozygotes are attributed to competition for a positive regulator.
Conclusions:
- Dominant-negative let-60 mutations provide insights into ras protein function and regulation.
- These mutations can cause severe developmental defects, including dominant lethality at high doses.
- The study suggests separable domains for activator interaction and physiological effect in ras proteins.
- let-60(dn) mutations may serve as valuable tools for dissecting ras-mediated signaling in other organisms.
