A transient specialization of the microtubule cytoskeleton is required fordifferentiation of the Drosophila visual system

Drosophila beta 3-tubulin is an essential isoform expressed during differen tiation of many cell types in embryos and pupae. We report here that during pupal development transient beta 3 expression demarcates a unique subset o f neurons in the developing adult visual system. beta 3 is coassembled into microtubules with beta 1, the sole beta-tubulin isoform in the permanent m icrotubule cytoskeleton of the adult eye and brain. Examination of beta 3 m utant phenotypes showed that beta 3 is required for axonal patterning and c onnectivity and for spatial positioning within the optic lobe. Comparison o f the phenotypes of P3 mutations with those that result from disruption of the Hedgehog signaling pathway shows that beta 3 functions early in the est ablishment of the adult visual system. Our data support the hypothesis that beta 3 confers specialized properties on the microtubules into which it is incorporated. Thus a transient specialization of the microtubule cytoskele ton during differentiation of a specific subset of the neurons has permanen t consequences for later cell function. (C) 2000 Academic Press.