The Axonal Localization of Large Drosophila Ankyrin 2 Protein Isoforms is Important for Neuronal Functionality. M. Hortsch ¹, K.L. Paisley ¹, M.-T. Tian ¹, M. Qian ¹, M. Bouley ¹, R. Chandler ². 1) Dept. Cell & Developmental Biology, Univ. of Michigan, Ann Arbor, MI; 2) Dept. Biology, Union College, Barbourville, KY.

   In polarized cells, such as neurons, ankyrin-type proteins are the principal molecules that link the actin-spectrin-based membrane cytoskeleton to the plasma membrane. In Drosophila the first of the two ankyrin genes is ubiquitously expressed, whereas the second ankyrin gene, Dank2, is exclusively expressed in neuronal cells (Bouley et al., J. Neurosci. 20: 4515-23, 2000). Similar to ankyrin genes in other organisms, the Dank2 gene generates several ankyrin protein isoforms by differential splicing. Here we report that in Drosophila, the short Dank2 protein isoform is restricted to neuronal cell bodies and is excluded from axons, whereas the long Dank2 isoforms are localized specifically to axons. Thus in vivo the composition of the neuronal cortical cytoskeleton is highly polarized. We also show that once polarization is established in all neurons, it persists during later stages of Drosophila development. In addition, we present genetic evidence that the absence of axonal Dank2 protein is lethal in Drosophila. Therefore, axonal Dank2 protein must fullfill some essential function(s) in Drosophila neuronal cells. Most neuronal ankyrin ligands are cell adhesion and axonal pathfinding molecules and the membrane skeleton has been postulated to position and anchor these proteins in the neuronal plasma membrane. In Drosophila neurons the neural cell adhesion molecule Neuroglian is a major membrane protein ligand of Dank2. However, axonal Dank2 is not required for transporting Neuroglian protein to the axonal subcellular compartment of Drosophila neurons. This suggests that the axonal membrane skeleton appears to be involved in the local organization molecules such as Neuroglian, rather than the long-range recruitment of these proteins to specific subcellular compartments.