A Role for EK4 in Kinesin Driven Axonal Transport. A. Gassman , O. Klyachko , W. Saxton. Dept. of Biology, Indiana University, Bloomington, IN.

   The microtubule based motor protein Kinesin I is essential for maintaining proper neuronal structure and function. Mutations in the Drosophila Kinesin heavy chain gene (Khc) cause axonal swellings that are filled with vesicles and other organelles in larval segmental nerves. This and a variety of other observations suggest that Kinesin I acts as a motor for the anterograde transport of organelles in axons. To better understand how Kinesin I works in neurons we are identifying mutations that act as dominant enhancers of Khc mutations. The enhancers act as second-site noncomplementers, generating synthetic Khc-like neuronal phenotypes in double heterozygotes (e.g. Khc/+; ek/+). One such enhancer, ek4, also causes Khc-like neuronal phenotypes when homozygous in a wild-type Khc background. Preliminary results suggest that the mutant allele is due to a point mutation in a gene for a Drosophila homolog of Jnk Interacting Proteins 1 and 2 (JIP). Mammalian JIP 1 and 2 are scaffolding proteins for the c-Jun NH ₂-terminal kinase signaling cascade. Mammals also have a scaffolding protein called JIP 3 or JSAP, which shares no sequence similarity with JIP 1 and 2. In Drosophila there are only two JIPs, the JIP1/2 homologue linked to ek4 (DJIP1/2) and a JSAP homolog. The JSAP homolog corresponds to Sunday driver which may interact directly with Drosophila Kinesin light chain to help anchor Kinesin I to membranes (Bowman et al.2000). Indirect immunoflouresence with antibodies generated against a mammalian JIP 1 peptide, (courtesy of Debra Meyer and Ben Margolis), suggest that Drosophila JIP1/2 is concentrated in some synaptic terminals and neuronal cell bodies in larvae. In Khcmutants, the JIP antibody staining is mislocalized in what appear to be axonal swellings along the lengths of a subset of axons in segmental nerves. We are exploring the possibility that DJIP1/2 acts as both a Kinesin I-cargo linker and a Kinesin I regulator in fast axonal transport.