Plug-and-play genetic access to drosophila cell types using exchangeable exon cassettes.

Genetically encoded effectors are important tools for probing cellular function in living animals, but improved methods for directing their expression to specific cell types are required. Here, we introduce a simple, versatile method for achieving cell-type-specific expression of transgenes that leverages the untapped potential of "coding introns" (i.e., introns between coding exons). Our method couples the expression of a transgene to that of a native gene expressed in the cells of interest using intronically inserted "plug-and-play" cassettes (called "Trojan exons") that carry a splice acceptor site followed by the coding sequences of T2A peptide and an effector transgene. We demonstrate the efficacy of this approach in Drosophila using lines containing suitable MiMIC (Minos-mediated integration cassette) transposons and a palette of Trojan exons capable of expressing a range of commonly used transcription factors. We also introduce an exchangeable, MiMIC-like Trojan exon construct that can be targeted to coding introns using the Crispr/Cas system.

This work was supported by the Intramural Research Program of the National Institute of Mental Health (B.H.W.) and by grants from the Whitehall Foundation (C.J.P.), NIH (R01DC013070, C.J.P.), the Wellcome Trust (H.I. and M.L.), and the Sir Isaac Newton Trust, Cambridge (M.L.). J.E. was supported by FONDECYT #1141278 and the CINV, which is supported by the Millennium Scientific Initiative of the Ministerio de Economía, Fomento y Turismo. We thank the Bellen laboratory and the Drosophila Gene Disruption Project at Baylor College of Medicine, the Bloomington Stock Center (NIH P40OD018537), and Julie Simpson for fly lines. Thanks also to Aaron DiAntonio, Aaron Hsueh, and John Reinitz for antibodies and the NINDS Sequencing Core Facility for DNA sequencing. Finally, thanks to Sarah Naylor for technical help and Grace Gray, Herman Dierick, Koen Venken, and Hugo Bellen for comments on the manuscript and productive discussions.

This is the final published version. It first appeared at http://www.ncbi.nlm.nih.gov/pubmed/25732830.