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The C. elegans MDL-1 and MXL-1 proteins can functionally substitute for vertebrate MAD and MAX
J Yuan1, R S Tirabassi, A B Bush
1Department of Molecular Biology, Princeton University, New Jersey 08544-1014, USA.
Abstract:
The genes of the myc/max/mad family play an important role in controlling cell proliferation and differentiation. We have identified the first homologues of the mad and max genes in the nematode C. elegans, which we have named mdl-1 and mxl-1 respectively. Like the vertebrate MAD proteins, MDL-1 binds an E-box DNA sequence (CACGTG) when dimerized with MXL-1. However, unlike vertebrate MAX, MXL-1 can not form homodimers and bind to DNA alone. Promoter fusions to a GFP reporter suggest that these genes are coexpressed in posterior intestinal and post-mitotic neuronal cells during larval development. The coexpression in the posterior intestinal cells occurs before their final division at the end of the L1 stage and persists afterwards, demonstrating that mad and max expression can be correlated directly to the cell cycle state of an individual cell type. These data also show that mxl-1 is an obligate partner for mdl-1 in vivo and in vitro and indicate that these genes may play an important role in post-embryonic development. Finally, MDL-1 can suppress activated c-MYC/RAS-induced focus formation in a rat embryo fibroblast transformation assay. Like the vertebrate MAD protein, MDL-1 activity in suppressing transformation is dependent on a functional SIN3 interaction domain.
Insights
Researchers identified C. elegans mdl-1 and mxl-1 genes, homologs of myc/max/mad family members. These genes are crucial for cell proliferation and differentiation, with MDL-1 suppressing transformation, highlighting their role in development.
Area of Science:
- Molecular Biology
- Developmental Biology
- Genetics
Background:
- The myc/max/mad gene family is critical for regulating cell proliferation and differentiation.
- Understanding these pathways in model organisms aids in deciphering conserved biological processes.
Purpose of the Study:
- Identify and characterize the first C. elegans homologs of mad and max genes.
- Investigate the interaction and function of these genes in C. elegans development.
- Determine the role of MDL-1 in cellular transformation.
Main Methods:
- Gene identification and nomenclature (mdl-1, mxl-1).
- In vitro DNA binding assays to study protein dimerization and DNA interaction.
- Promoter-GFP fusions to analyze gene expression patterns during larval development.
- Rat embryo fibroblast transformation assay to assess MDL-1's tumor suppressor activity.
Main Results:
- MDL-1 and MXL-1 were identified as C. elegans homologs of vertebrate MAD and MAX proteins.
- MDL-1 binds DNA as a heterodimer with MXL-1, but MXL-1 does not form homodimers.
- mdl-1 and mxl-1 are coexpressed in posterior intestinal and neuronal cells, correlating with cell cycle state.
- MDL-1 suppresses activated c-MYC/RAS-induced transformation, dependent on its SIN3 interaction domain.
Conclusions:
- MXL-1 is an essential partner for MDL-1 function in vivo and in vitro.
- mdl-1 and mxl-1 likely play significant roles in C. elegans post-embryonic development.
- MDL-1 exhibits tumor suppressor activity, similar to vertebrate MAD proteins, through its SIN3 interaction domain.