The Identification and Characterization of a New Protein Essential for Drosophila Myotendinous Junction Formation. Zongheng Wang. University of Missouri-Kansas City, Kansas City, MO.

   The myotendinous junction (MTJ) provides the primary site to transmit the force generated during muscle contraction from the interior of the muscle cell, across its membrane and the extracellular matrix (ECM), to the epithelial tendon cell for locomotion. It has been reported that any decrease in MTJ formation and/or stability leads to muscle detachment in diverse organisms, which underlies a series of congenital, progressive myopathies in humans. While it is know that integrins are required to form cohesive attachments with the ECM that lies between the muscle and tendons, the molecular mechanisms that govern formation and maintenance of MTJs in any model system are poorly understood. As an entry point to uncover proteins that contribute to MTJ development and maintenance, we utilized an in vivo proteomics approach. We have identified three new proteins that are required for the stable attachments of muscles to their target tendon cells. One of these evolutionarily conserved candidates, named Clueless (Clu), has been chosen for further study. A series of clu mutant alleles were generated using P-element excision techniques. Immunostaining using an antibody against Myosin heavy chain reveals that the muscles in clu mutant embryos migrate to their target tendon cells. Moreover, the expression and localization of molecular markers that function in muscle migration, such as dGit1 and activated focal attachment kinase, are not affected in the clu mutant embryos. However, upon muscle contraction, the muscles detach from their corresponding tendon cells and round up. The expression of integrin components at the MTJ is reduced in clu mutant embryos, suggesting a failure to form strong interactions between the muscle and the tendon cell. Other data will be presented to determine in what cell type Clu functions in muscle-tendon attachment; and how Clu functions at the molecular level to mediate proper MTJ formation and/or maintenance.