A Transient Specialization of the Microtubule Cytoskeleton Is Required for Differentiation of the DrosophilaVisual System

Drosophilaβ3-tubulin is an essential isoform expressed during differentiation of many cell types in embryos and pupae. We report here that during pupal development transient β3 expression demarcates a unique subset of neurons in the developing adult visual system. β3 is coassembled into microtubules with β1, the sole β-tubulin isoform in the permanent microtubule cytoskeleton of the adult eye and brain. Examination of β3 mutant phenotypes showed that β3 is required for axonal patterning and connectivity and for spatial positioning within the optic lobe. Comparison of the phenotypes of β3 mutations with those that result from disruption of the Hedgehog signaling pathway shows that β3 functions early in the establishment of the adult visual system. Our data support the hypothesis that β3 confers specialized properties on the microtubules into which it is incorporated. Thus a transient specialization of the microtubule cytoskeleton during differentiation of a specific subset of the neurons has permanent consequences for later cell function.