The organization of INAD-signaling complexes by a multivalent PDZ domain protein in Drosophila photoreceptor cells ensures sensitivity and speed of signaling

Phototransduction in Drosophila has emerged as an attractive model system f or studying the organization of signaling cascades in vivo. In photorecepto r neurons, the multivalent PDZ protein INAD serves as a scaffold to assembl e different components of the phototransduction pathway, including the effe ctor PLC, the light-activated ion channel TRP, and a protein kinase C invol ved in deactivation of the light response. INAD is required for organizing and maintaining signaling complexes in the rhabdomeres of photoreceptors. T his macromolecular organization endows photoreceptors with many of their si gnaling properties, including high sensitivity, fast activation and deactiv ation kinetics, and exquisite feedback regulation by small localized change s in [Ca2+](i). Assembly of transduction components into signaling complexe s is also an important cellular strategy for ensuring specificity of signal ing while minimizing unwanted cross-talk. In this report, we review INAD's role as a signal transduction scaffold and its role in the assembly and loc alization of photoreceptor complexes. (C) Harcourt Publishers Ltd.