A transient specialization of the microtubule cytoskeleton is required for differentiation of the Drosophila visual system.

Drosophila beta3-tubulin is an essential isoform expressed during differentiation of many cell types in embryos and pupae. We report here that during pupal development transient beta3 expression demarcates a unique subset of neurons in the developing adult visual system. beta3 is coassembled into microtubules with beta1, the sole beta-tubulin isoform in the permanent microtubule cytoskeleton of the adult eye and brain. Examination of beta3 mutant phenotypes showed that beta3 is required for axonal patterning and connectivity and for spatial positioning within the optic lobe. Comparison of the phenotypes of beta3 mutations with those that result from disruption of the Hedgehog signaling pathway shows that beta3 functions early in the establishment of the adult visual system. Our data support the hypothesis that beta3 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. Copyright 2000 Academic Press.