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Mutational analysis of the Caenorhabditis elegans cell-death gene ced-3
S Shaham1, P W Reddien, B Davies
1Howard Hughes Medical Institute, Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Abstract:
Mutations in the gene ced-3, which encodes a protease similar to interleukin-1beta converting enzyme and related proteins termed caspases, prevent programmed cell death in the nematode Caenorhabditis elegans. We used site-directed mutagenesis to demonstrate that both the presumptive active-site cysteine of the CED-3 protease and the aspartate residues at sites of processing of the CED-3 proprotein are required for programmed cell death in vivo. We characterized the phenotypes caused by and the molecular lesions of 52 ced-3 alleles. These alleles can be ordered in a graded phenotypic series. Of the 30 amino acid sites altered by ced-3 missense mutations, 29 are conserved with at least one other caspase, suggesting that these residues define sites important for the functions of all caspases. Animals homozygous for the ced-3(n2452) allele, which is deleted for the region of the ced-3 gene that encodes the protease domain, seemed to be incompletely blocked in programmed cell death, suggesting that some programmed cell death can occur independently of CED-3 protease activity.
Insights
Mutations in the ced-3 gene, which encodes a protease essential for programmed cell death in C. elegans, prevent this crucial cellular process. Key residues within the CED-3 protease are vital for its function in apoptosis.
Area of Science:
- Molecular Biology
- Developmental Biology
- Genetics
Background:
- Programmed cell death, or apoptosis, is a fundamental biological process.
- The gene ced-3 in Caenorhabditis elegans encodes a protease homologous to mammalian caspases, key executioners of apoptosis.
- Understanding ced-3 function is critical for deciphering apoptosis pathways.
Purpose of the Study:
- To investigate the essential domains and residues of the CED-3 protease required for programmed cell death in C. elegans.
- To characterize the functional consequences of various ced-3 mutations.
Main Methods:
- Site-directed mutagenesis was employed to alter specific residues within the CED-3 protease.
- Analysis of 52 distinct ced-3 alleles, including missense and deletion mutations.
- Phenotypic characterization of mutant animals and molecular lesion identification.
Main Results:
- Both the active-site cysteine and specific aspartate residues involved in CED-3 proprotein processing are crucial for programmed cell death.
- A graded series of phenotypes was observed across the 52 characterized ced-3 alleles.
- 29 out of 30 altered amino acid sites in missense mutations are conserved across caspases, highlighting their functional importance.
- A deletion mutant (ced-3(n2452)) showed incomplete blockage of cell death, suggesting CED-3-independent pathways.
Conclusions:
- The CED-3 protease activity is essential for the majority of programmed cell death events in C. elegans.
- Conserved residues in CED-3 likely play critical roles in the function of all caspases.
- Evidence suggests that some programmed cell death can occur independently of CED-3 protease activity.