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Suppression of the rbf null mutants by a de2f1 allele that lacks transactivation domain
W Du1
1Ben May Institute for Cancer Research and Center for Molecular Oncology, The University of Chicago, Chicago, IL, USA. wdu@ben-may. bsd.uchicago.edu
Abstract:
In mammals, a large number of proteins including E2F transcription factors have been shown to interact with the tumor suppressor gene product pRB, but it is not clear to what extend the function of pRB is mediated by E2F. In addition, E2F was shown to mediate both transcription activation and repression; it remains to be tested which function of E2F is critical for normal development. Drosophila homologs of the RB and E2F family of proteins RBF and dE2F1 have been identified. The genetic interactions between rbf and de2f1 were analyzed during Drosophila development, and the results presented here showed that RBF is required at multiple stages of development. Unexpectedly, rbf null mutants can develop until late pupae stage when the activity of dE2F1 is reduced, and can develop into viable adults with normal adult appendages in the presence of a de2f1 mutation that retains the DNA binding domain but lacks the transactivation domain. These results indicate that most, if not all, of the function of RBF during development is mediated through E2F. In turn, the genetic interactions shown here also suggest that dE2F1 functions primarily as a transcription activator rather than a co-repressor of RBF during Drosophila development. Analysis of the expression of an E2F target gene PCNA in eye discs showed that the expression of PCNA is activated by dE2F1 in the second mitotic wave and repressed in the morphogenetic furrow and posterior to the second mitotic wave by RBF. Interestingly, reducing the level of RBF restored the normal pattern of cell proliferation in de2f1 mutant eye discs but not the expression of E2F target genes, suggesting that the coordinated transcription of E2F target genes does not significantly affect the pattern of cell proliferation.
Insights
The tumor suppressor protein RBF
Area of Science:
- * Developmental Biology
- * Molecular Genetics
- * Cell Cycle Regulation
Background:
- * The retinoblastoma protein (pRB) and E2F transcription factors are key regulators of cell proliferation and development in mammals.
- * The precise mechanisms by which pRB influences E2F activity, including transcription activation versus repression, remain incompletely understood.
- * Drosophila melanogaster offers a powerful genetic model to investigate conserved developmental pathways.
Purpose of the Study:
- * To elucidate the functional relationship between RBF (Drosophila pRB homolog) and dE2F1 (Drosophila E2F1 homolog) during development.
- * To determine whether RBF's developmental functions are mediated through dE2F1.
- * To clarify the role of dE2F1 as a transcription activator or repressor in conjunction with RBF.
Main Methods:
- * Genetic interaction analysis between mutations in the rbf and de2f1 genes in Drosophila.
- * Phenotypic analysis of rbf and de2f1 mutant Drosophila during various developmental stages.
- * Examination of PCNA gene expression in Drosophila eye discs using genetic manipulation.
Main Results:
- * RBF null mutants exhibit developmental delays, with rescue observed in the presence of reduced dE2F1 activity or a non-transactivating dE2F1 mutant.
- * These findings strongly suggest that RBF primarily functions through E2F during Drosophila development.
- * dE2F1 acts mainly as a transcription activator, while RBF represses PCNA expression in specific regions of the eye disc.
Conclusions:
- * The majority of RBF's developmental functions in Drosophila are mediated by dE2F1.
- * dE2F1 functions predominantly as a transcriptional activator in this context.
- * While RBF influences cell proliferation patterns, the coordinated transcription of E2F target genes is not essential for this regulation.