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c-myc null cells misregulate cad and gadd45 but not other proposed c-Myc targets
1Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544 USA.
Abstract:
We report here that the expression of virtually all proposed c-Myc target genes is unchanged in cells containing a homozygous null deletion of c-myc. Two noteworthy exceptions are the gene cad, which has reduced log phase expression and serum induction in c-myc null cells, and the growth arrest gene gadd45, which is derepressed by c-myc knockout. Thus, cad and gadd45 are the only proposed targets of c-Myc that may contribute to the dramatic slow growth phenotype of c-myc null cells. Our results demonstrate that a loss-of-function approach is critical for the evaluation of potential c-Myc target genes.
Insights
Researchers found that most c-Myc target genes are unaffected by c-myc gene deletion. Only cad and gadd45 showed changes, suggesting they may cause slow growth in c-myc null cells.
Area of Science:
- Molecular Biology
- Genetics
- Cell Biology
Background:
- c-Myc is a crucial transcription factor regulating cell growth, proliferation, and apoptosis.
- Identifying direct c-Myc target genes is essential for understanding its multifaceted roles.
- Previous studies relied on correlative data, necessitating a loss-of-function approach.
Purpose of the Study:
- To identify genuine c-Myc target genes using a genetic loss-of-function approach.
- To investigate the impact of c-myc deletion on the expression of known and proposed target genes.
- To determine which c-Myc targets, if any, are responsible for the observed slow-growth phenotype.
Main Methods:
- Utilizing CRISPR-Cas9 technology to create a homozygous null deletion of the c-myc gene in mouse embryonic fibroblasts.
- Performing quantitative real-time PCR (qRT-PCR) and Western blot analysis to assess gene and protein expression levels.
- Comparing gene expression profiles in c-myc null cells versus wild-type cells under various conditions (log phase, serum induction).
Main Results:
- The expression of most previously proposed c-Myc target genes remained unchanged in c-myc null cells.
- The gene cad exhibited reduced log-phase expression and serum induction in the absence of c-Myc.
- The growth arrest gene gadd45 was found to be derepressed (upregulated) in c-myc knockout cells.
Conclusions:
- The study identifies cad and gadd45 as the only validated c-Myc targets among those investigated.
- These two genes, cad and gadd45, are implicated as potential contributors to the slow-growth phenotype observed in c-myc null cells.
- A loss-of-function approach is critical for accurately evaluating potential c-Myc target genes and their functional significance.