Kakapo orchestrates a unique microtubule-associated plaque at the muscle-tendon junction site, rich with integrin mRNA. A. Subramanian , T. Volk. Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 76100, Israel.

   Kakapo is a Drosophila intracellular cytoskeletal-associated protein, conserved in vertebrates. It is expressed in ectodermaly derived cells including tendons and neurons and known to play an important role in muscle-tendon junction formation, neuromuscular synapse formation, neuronal extension and wing development. We have analyzed the role of Kakapo following the establishment and maintenance of muscle-tendon junction at third instar larval stage. Co-precipitation analysis reveals that the individual domains in Kakapo show a binding profile with actin and tubulin. Consistent with the co-precipitation experiments; Kakapo is detected in high levels at a unique microtubule-associated plaque formed at the cytoplasmic faces of the muscle-tendon junction. A thin layer of microfilaments which is detected distinctly at the cytoplasmic faces of the muscle-tendon junction overlaps with Kakapo suggesting that Kakapo crosslinks the microtubules and actin layers at the junction. The physical association of Kakapo with microtubule binding proteins including APC, EB1 and PAR1 is currently studied. Insitu hybridization analysis of wild type larvae has revealed the accumulation of PSb-integrin mRNA at the cytoplasmic faces of the muscle-tendon junction, coinciding with the microtubule associated plaque. This plaque is disrupted following specific expression of double stranded kakapo RNA in tendon cells. Our results suggest that Kakapo organizes a unique microtubule based plaque at the muscle-tendon junction site, and cross-links it to the microfilament layer at this region. The possibility that this plaque may serve as a scaffold for the localization of junction specific mRNAs is currently being studied.