The Drosophila nuclear factor DREF positively regulates the expression of the mitochondrial transcription termination factor DmTTF
Résumé
The DNA Replication-related Element-binding Factor (DREF), which regulates transcription of a group of cell proliferation-related genes in Drosophila, controls also the expression of three genes involved in mitochondrial DNA (mtDNA) replication and maintenance. In this study, by in silico analysis, we have identified DNA Replication-related Elements (DRE) in the promoter region of a gene participating in mtDNA transcription, the Drosophila mitochondrial Transcription Termination Factor (DmTTF). Transient transfection assays in Drosophila S2 cells, with mutated versions of DmTTF promoter region, showed that DRE elements control DmTTF transcription; moreover, gel-shift and ChIP assays demonstrated that the analysed DRE sites interact with DREF either in vitro and in vivo. Accordingly, DREF knockdown in S2 cells by RNA interference induced a considerable decrease in DmTTF mRNA level. These results clearly demonstrate that DREF positively controls DmTTF expression. On the contrary, mitochondrial RNA polymerase (mtRNApol) lacks DRE elements in its promoter and is not regulated in vivo by DREF. In situ RNA hybridization studies showed that DmTTF was transcribed almost ubiquitously throughout all stages of Drosophila embryogenesis, whereas mtRNApol was efficiently transcribed from stages 11th-12th. Territories where transcription occurred mostly were gut and Malpighi tubes for DmTTF, and gut, mesoderm, pharyngeal muscle and Malpighi tubes for mtRNApol. The partial overlapping in the temporal and spatial mRNA expression patterns confirms that transcription of the two genes is differentially regulated during embryogenesis and suggests that DmTTF might play multiples roles in mtDNA transcription process, for which different levels of the protein with respect to mtRNApol are required.
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