TAU-BETA-GALACTOSIDASE, AN AXON-TARGETED FUSION PROTEIN

The most commonly used enzymatic reporter molecule, Escherichia coli b eta-galactosidase (beta-gal; beta-D-galactoside galactohydrolase, EC 3 .2.1.23), fails to readily diffuse into axons; consequently, the morph ologies of beta gal-labeled neurons cannot directly be determined. For analysis of neuronal pathfinding and synaptic connectivity, this info rmation is essential. We have constructed an axon-targeted beta-gal re porter by fusing the cDNA encoding the bovine microtubule-binding prot ein, tau, to lacZ, the E. coli gene encoding beta-gal. This reporter l abels cell bodies and axons when expressed by developing and adult Dro sophila neurons. It also reveals the entire cellular extent of nonneur onal cells such as muscle fibers and glia. To generate neuronal marker s for studies of Drosophila neural development, we constructed a tau-b eta-gal enhancer-trap transposon. From 1500 independent lines generate d by mobilization of this transposon, we have isolated a set of useful markers for specific subsets of neurons, glia, and muscles. Since the tau cDNA-lacZ reporter utilizes bovine tau, it may also effectively t arget beta-gal in vertebrate neurons and prove to be a useful reagent for the analysis of vertebrate nervous systems.