A wealth of tools to manipulate gene action in vivo has brought a new level of sophistication to studies of the invertebrate model Drosophila, largely through the use of a bipartite transcriptional regulatory system adapted from yeast. In this system, the transcription factor Gal4 binds to specific DNA sequences upstream of target genes to activate their transcription. By introducing these upstream activating sequences (UAS) next to a minimal promoter and any gene of interest, high levels of expression are obtained in the presence of Gal4. Other regulatory components include Gal80, a repressor that binds to Gal4 and limits its activity. By building both temporal and spatial control into the GAl4/UAS system for the fly, any gene can be induced in a given cell or tissue at a given time. This powerful approach has not only enhanced developmental studies and the generation of new disease models, but has provided insights into how neurons mediate complex behaviors in the adult brain. The goal of the proposed work is to expand upon and optimize the versatile Gal4/UAS system for the vertebrate model, the zebrafish. In initial studies, a new vector was produced that integrates throughout the zebrafish genome by transposition, thereby placing the Gal4 gene under the control of adjacent tissue-specific enhancers. Moreover, these gene/enhancer traps could activate other genes under UAS control, including fluorescent reporters of sub-cellular structure and effectors of cell death. Numerous researchers have requested plasmid constructs and the Gal4 driver and UAS reporter transgenic lines produced from this work. While robust, tissue-restricted expression is routinely achieved now in zebrafish, there is no reliable method to control gene expression temporally. Several approaches have been successfully used in Drosophila and will be tested for their efficacy to induce Gal4 activity in transgenic zebrafish. Some recovered transgenic lines show pronounced transcriptional silencing at the level of the UAS. Another aim of this study is to take advantage of these insertions to gain a greater understanding of how UAS regulated genes are silenced, with the goal of designing new transgenic vectors less susceptible to transcriptional repression. In addition, a battery of new tools under UAS control will be produced that will have broad utility in observing cellular morphology real-time, in long-term lineage studies and in mapping neuronal connectivity in the brain. The proposed collection of tools will bring a new and much needed versatility to zebrafish experimentation and, as with our first set of Gal4/UAS transgenic lines, will serve as a valuable resource for the research community.
The ability to manipulate gene expression in time and space using the Gal4/UAS transcriptional activation system of yeast revolutionized experimental approaches in the Drosophila model. Versatile Gal4-based methods allow researchers to visualize subsets of cells or sub-cellular structures with fluorescent markers, to monitor processes that underlie organ formation real-time, to asses protein function in selective tissues or cells, and to discover new genes acting in genetic pathways. The application of this methodology to zebrafish has unlimited potential and is sorely needed to address processes beyond early development, such as adult physiology and behavior. The proposed experiments are aimed at continuing a productive collaborative effort between three research groups to generate new Gal4/UAS transgenic tools for regulated gene expression in the zebrafish. An additional goal is to optimize the Gal4/UAS system by exploring the basis of transcriptional silencing of zebrafish transgenes and devising approaches to overcome it.
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