Regulation of axon outgrowth during mushroom body development by acetylated α-tubulin lysine 394 and tau

Abstract Disruptions in the microtubule cytoskeleton play a role in various neurological diseases that afflict a large fraction of the population. Microtubule function is regulated by post-translational modifications like acetylation, and one consistently identified acetylation site in mammals and Drosophila melanogaster is α-tubulin lysine 394 (K394). Our previous research demonstrated that an acetylation-blocking point mutation—K394R—causes a decrease in microtubule stability in axon terminals at the developing neuromuscular junction. Here, we asked whether K394 acetylation regulates the development of additional neuronal structures. Using the central brain mushroom body as a model, we found that K394R results in β lobe overextension at the midline. The K394R phenotype manifests during metamorphosis and affects β lobe growth in a cell-autonomous manner. Our data suggest that the K394R phenotype may result from changes in Tau, a microtubule-associated protein enriched in the mushroom body and known to play a critical role in regulating neuronal microtubules. Knocking-out tau resulted in defects in midline crossing similar to K394R. However, when the loss of tau was combined with K394R, β lobe extension was normal—indicating that the loss of tau suppresses the K394R phenotype and vice versa. While overexpressing tau also resulted in a midline crossing phenotype, K394R in combination with elevated Tau resulted in a severely malformed mushroom body. Altogether, our work suggests that K394R interacts with tau to regulate axon outgrowth during mushroom body development and raises the potential of manipulating K394 acetylation to ameliorate neurological disease resulting from axonal growth defects and changes in Tau.