Embryonic expression of the divergent drosophila beta 3-tubulin isoform isrequired for larval behavior

We have sought to define the developmental and cellular roles played by dif ferential expression of distinct beta -tubulins. Drosophila beta3-tubulin ( beta3) is a structurally divergent isoform transiently expressed during mid embryogenesis. Severe beta3 mutations cause larval lethality resulting from failed gut function and consequent starvation. However, mutant larvae also display behavioral abnormalities consistent with defective sensory percept ion. We identified embryonic beta3 expression in several previously undefin ed sites, including different types of sensory organs. We conclude that abn ormalities in foraging behavior and photoresponsiveness exhibited by prelet hal mutant larvae reflect defective beta3 function in the embryo during dev elopment of chordotonal and other mechanosensory organs and of Bolwig's org an and nerve. We show tl-tat microtubule organization in the cap cells of c hordotonal organs is altered in mutant larvae. Thus transient zygotic beta3 expression has permanent consequences for the architecture of the cap cell microtubule cytoskeleton in the larval sensilla, even when beta3 is no lon ger present. Our data provide a link between the microtubule cytoskeleton i n embryogenesis and the behavioral phenotype manifested as defective propri oreception at the larval stage.