| Summary: | C. elegans is an excellent model organism for the study of muscle development and maintenance, but we lack a full catalog of genes involved and their specific roles. I have identified and characterized two novel genes, pxl-1 which is essential in C. elegans pharyngeal muscle and cpna-1 which is essential in body wall muscle. PXL-1 is the C. elegans homolog of vertebrate paxillin and contains the four C-terminal LIM domains conserved in paxillin across all species and three of the five LD motifs found in the N- terminal half of most paxillins. PXL-1 antibodies and a full-length GFP translational fusion localize to muscle adhesion sites in the sarcomere, the functional repeat unit in muscle responsible for contraction. In pharyngeal muscle, PXL-1 localizes to ring-shaped structures near the sarcolemma corresponding to podosome-like sites of actin attachment. Loss of paxillin results in lack of pharyngeal contraction, developmental arrest, and lethality. Expression of paxillin solely in the pharynx results in wild type in movement and body wall muscle structure. This demonstrates that in pharyngeal muscle PXL-1 is essential for contraction, whereas in body wall muscle it is dispensable for filament assembly, sarcomere stability, and ultimately movement.
CPNA-1 is a copine domain protein essential for myofilament stability and viability in C. elegans. Worms lacking cpna-1 arrest at the two-fold stage of embryogenesis and have disruption of the myofilament lattice. CPNA-1 contains an N- terminal trans-membrane domain, and a copine domain near its C-terminal. Both a GFP translational fusion and antibody specific to CPNA-1 localize to muscle adhesion sites in body wall muscle. CPNA-1 also binds to components of muscle adhesion sites including UNC-89 (obscurin), and the essential muscle protein PAT-6 (actopaxin), which CPNA-1 requires for localization. The essential MYO-3 (heavy chain myosin) protein is initially localized normally in cpna-1 null animals, but becomes mislocalized as contraction begins indicating CPNA-1 is not required for initial assembly of the sarcomere, but is required to maintain structural stability through development. Together, the characterization of PXL-1 and CPNA-1 provide new insight into the organization of muscle adhesion sites in Caenorhabditis elegans. === Science, Faculty of === Zoology, Department of === Graduate
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