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Abstract

Tropomodulins are proteins widely expressed in all complex animals that help to regulate the shape of cells by modifying the cytoskeletal filament actin. C. elegans worms lacking the tropomodulin TMD-1 show defects in development of the excretory cell, which acts as a kidney for the worm. The excretory cell extends four canals out from the cell body so that the entire cell looks like a great letter H stretching the length of the worm. In tmd-1 mutants, canals extend partially or not at all, and develop a dramatic crinkled appearance. The mechanism for this interference is unknown; however several possibilities are being explored. Excretory canals are often affected by mutations in genes, also needed in neuronal axon guidance. Knocking down one of these guidance proteins, MIG-10, produced a similar phenotype to that of the tmd-1 mutants. However, further experiments did not uncover any neuronal guidance defects in tmd-1 mutants. Instead, it is more likely that TMD-1 is essential for vesicle trafficking within the excretory canal. In this function TMD-1 may facilitate canal extension by providing membrane components to the growing canal tips. Insight into tropomodulin’s role in single-celled tube formation can further our understanding of how these tubes form in many organisms.

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