No abstract

2Protein isoforms generated by alternative splicing contribute to proteome diversity. Due 3 to the lack of effective techniques, isoform-specific functions, expression, localization, 4 and signaling mechanisms of endogenous proteins in vivo are unknown for most genes. 5Here we report a genetic method, termed isoTarget, for blocking the expression of a 6 targeted isoform without affecting the other isoforms and for conditional tagging the 7 targeted isoform for multi-level analyses in select cells. Applying isoTarget to two 8 mutually exclusive isoforms of Drosophila Dscam, Dscam[TM1] and [TM2], we found 9 that endogenous Dscam[TM1] is localized in dendrites while Dscam[TM2] is in both 10 dendrites and axons. We demonstrate that the difference in subcellular localization 11 between Dscam[TM1] and [TM2], rather than any difference in biochemical properties, 12leads to the two isoforms' differential contributions to dendrite and axon development. 13 Moreover, with isoTarget, we discovered that the subcellular enrichment of functional 14 partners results in a DLK/Wallenda-Dscam[TM2]-Dock signaling cascade specifically in 15 axons. isoTarget is an effective technique for studying how alternative splicing 16 enhances proteome complexity.Hing, H., Xiao, J., Harden, N., Lim, L., and Zipursky, S.L. (1999). Pak functions 1 downstream of Dock to regulate photoreceptor axon guidance in Drosophila. Cell 97, 2 853-863.