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A genetic screen for modifiers of E2F in Drosophila melanogaster
K Staehling-Hampton1, P J Ciampa, A Brook
1Massachusetts General Hospital Cancer Center, Charlestown, Massachusetts 02129, USA.
Abstract:
The activity of the E2F transcription factor is regulated in part by pRB, the protein product of the retinoblastoma tumor suppressor gene. Studies of tumor cells show that the p16(ink4a)/cdk4/cyclin D/pRB pathway is mutated in most forms of cancer, suggesting that the deregulation of E2F, and hence the cell cycle, is a common event in tumorigenesis. Extragenic mutations that enhance or suppress E2F activity are likely to alter cell-cycle control and may play a role in tumorigenesis. We used an E2F overexpression phenotype in the Drosophila eye to screen for modifiers of E2F activity. Coexpression of dE2F and its heterodimeric partner dDP in the fly eye induces S phases and cell death. We isolated 33 enhancer mutations of this phenotype by EMS and X-ray mutagenesis and by screening a deficiency library collection. The majority of these mutations sorted into six complementation groups, five of which have been identified as alleles of brahma (brm), moira (mor) osa, pointed (pnt), and polycephalon (poc). osa, brm, and mor encode proteins with homology to SWI1, SWI2, and SWI3, respectively, suggesting that the activity of a SWI/SNF chromatin-remodeling complex has an important impact on E2F-dependent phenotypes. Mutations in poc also suppress phenotypes caused by p21(CIP1) expression, indicating an important role for polycephalon in cell-cycle control.
Insights
Modifying E2F activity in Drosophila eyes revealed key regulators of cell-cycle control. Mutations in genes like brahma and polycephalon impact cell proliferation and may influence cancer development.
Area of Science:
- Molecular Biology
- Genetics
- Cancer Research
Background:
- E2F transcription factor activity is regulated by pRB, a tumor suppressor.
- Mutations in the p16(ink4a)/cdk4/cyclin D/pRB pathway are common in cancer, leading to cell-cycle deregulation.
- Extragenic mutations affecting E2F activity may play a role in tumorigenesis.
Purpose of the Study:
- To identify genetic modifiers of E2F activity using a Drosophila eye model.
- To understand the role of these modifiers in cell-cycle control and potential links to cancer.
Main Methods:
- Utilized an E2F overexpression phenotype in the Drosophila eye for genetic screening.
- Induced mutations using EMS and X-ray mutagenesis, and screened a deficiency library.
- Identified and characterized enhancer mutations, classifying them into complementation groups.
Main Results:
- Isolated 33 enhancer mutations affecting E2F activity.
- Identified five genes (brahma, moira, osa, pointed, polycephalon) as key modifiers.
- Discovered that osa, brahma, and moira encode components of a SWI/SNF chromatin-remodeling complex.
- Found that polycephalon mutations suppress p21(CIP1)-induced phenotypes.
Conclusions:
- A SWI/SNF chromatin-remodeling complex significantly impacts E2F-dependent phenotypes.
- Polycephalon plays a crucial role in cell-cycle control.
- These findings provide insights into cell-cycle regulation and potential therapeutic targets in cancer.