ANALYSES OF FUNCTIONS OF DNA REPLICATION REGULATORY FACTORS BY THE DROSOPHILA EYE-IMAGINAL DISC SPECIFIC EXPRESSION SYSTEM

点击翻译按钮获取中文摘要

Transgenic Drosophila lines expressing GAL4 specifically in the eye-imaginal discs were established. DREF cDNA and its fragments containing conserved regions 1,2 or 3 (CR1, CR2 or CR3) were ligated to the promoter containing GAL4-binding sites (UAS) in the P-element vector, and transgenic fly lines were established with these plasmid DNAs. These trnsgenic lines were utilized to examine effects of overexpression of DREF and its derivatives on eye development.Overexpression of the wild type DREF in eye imaginal discs caused abnormal eye morphology (rough eye phenotype). The rough eye phenotype is likely caused by the ectopic induction of DNA synthesis and apoptosis in the eye-imaginal disc cells. Since it is reported that overexpression of the transcription factor E2F can induce ectopic DNA synthesis, we have crossed the DREF-overexpressing flies with the E2F mutant flies. Half-reduction of the E2F gene copy number effectively suppressed the rough eye phenotype induced by overexpression of DREF, suggesting that DREF functions upstream of the E2F gene. Furthermore, we have cloned the E2F gene and found the three DRE-related sequences in the promoter region of the E2F gene. DREF specifically binds to these DRE-related sequences of the E2F gene promoter in vitro. Detailed analyses in vitro and in vivo demonstrated that DREF can activate the E2F gene promoter.In addition, overexpression of CRland CR3 of DREF in the eye imaginal discs also caused severe rough eye phenotype, In the eye discs of these flies, cells behind the morphogenetic furrow appeared to be arrested in G1 phase. Probably, CRland CR3 inhibited function of endogenous DREF in a dominant negative fashion to inhibit cells entering S phase.