Regulation mechanism of cell cycle by differentiation signals

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The DNA replication-related element-binding factor (DREF) has been suggested to be involved in regulation of DNA replication and proliferation-related genes in Drosophila. Over-expression of DREF induced ectopic DNA synthesis and apoptosis, and inhibited the photoreceptor cell differentiation in eye imaginal discs and adult flies exhibited a severe rough eye phenotype. We used DREF over-expressing fly lines as a tool to screen mutations that modify the rough eye phenotype. We identified 20 lines including eIF4a and skpA gene mutations that suppressed and 6 lines that enhanced the rough eye phenotype when they were heterozygous for the mutations. Since it is reported that eIF4a protein is associated with growth by regulating protein translation, regulation of eIF4a gene expression by DREF would be important for regulation of cell proliferation. SKPa is component of a Drosophila SCF complex that functions in combination with the ubiquitin conjugating enzyme UbcDl. DREF may therefore play … More roles in regulation of protein metabolism at the onset of cell proliferation.A yeast one-hybrid screen using three tandem repeats of DRE in dPCNA promoter as the bait allowed isolation of a cDNA encoding Cut, a Drosophila homologue of mammalian CCAAT-displacement protein (CDP)/Cux. Electrophoretic mobility shift assays showed that Cut bound to both DRE. Measurement of dPCNA promoter activity by.transient luciferase expression assays in Drosophila S2 cells after an RNA interference for Cut or DREF showed DREF activates the dPCNA promoter while Cut functions as a repressor. Chromatin immunoprecipitation assays in the presence or absence of 20-hydroxyecdysone further showed both DREF and Cut proteins to be localized in the genomic region containing the dPCNA promoter in S2 cells, especially in the Cut case upon induction of differentiation. These results indicate that Cut functions as a transcriptional repressor of dPCNA gene by binding to the promoter region in the differentiated state, while DREF binds to DRE to promote expression of dPCNA during cell proliferation. Less