Inducible GAL4 Systems for Gene Expression Control in Adult Drosophila melanogaster
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The ability to express a gene of interest in a directed place, time and at a certain level can be achieved by the use of gene expression control tools. The UAS/GAL4 system is by far the most widely used tool in Drosophila with a collection of thousands of GAL4 drivers available. Despite the system’s vast applications, the UAS/GAL4 system does not allow for temporal control of gene expression. A major focus of many fly geneticists has been to create a new system by generating new transgenes based on entirely different transcriptional regulators. However, it is much more convenient to take advantage of the existing UAS and/or GAL4 lines, many of which have previously been spatially and temporally characterized through adult life. Two new inducible GAL4-based gene expression systems were generated: the tetracycline inducible (Tet- Off) GAL80 transgenes and the lactose (Lac) Inducible UAS/GAL4 system. The Tet-Off GAL80 transgenes were designed to express GAL80 under the control of a Tet-Off promoter to regulate GAL4 activity. Two versions of the transgene were generated each with a unique ubiquitous promoter that drives expression of tTA. After exhaustively examining the repressive ability of this GAL80 system it was found that the best repression was achieved in genotypes with four copies and both versions of the transgene. Induction was observed in tetracycline treated animals but was found to be dependent on sex, age, and the anatomical location of transcription and translation. The repressive ability of GAL80 was also affected by age which would limit its use to regulate expression in adult animals. The Lac Inducible UAS/GAL4 System was designed to regulate the UAS promoter by incorporating lac operator (LacO) sequences to which LacI could bind and repress UAS transcriptional activity. Two different versions of the modified LacO-UAS were built previously containing 2 or 3 operators, pHN1 and pHN4. The influence of the addition of the lac operators was studied and found to negatively affect UAS transcriptional activity during adulthood, independent of LacI.
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