The Genetics of the Maintenance of Single-Celled Tube Diameter in C. elegans

The maintenance of diameter of biological tubes is essential for the continued functioning of many organismal functions.  The excretory canal cell of the nematode C. elegans provides a model of a long, narrow single-celled tube similar to those of mammalian capillaries and glia.  The canals extend along the entire length of the worm to regulate organismal osmolarity, and are maintained by proteins coded for by exc genes. EXC proteins maintain the diameter of the lumen of the canals, by assisting the trafficking of vesicles from early endosomes to recycling endosomes.  Mutations in the exc-9 gene cause shortened canals swollen into large, fluid-filled cysts.  EXC-9 is an excretory cell protein homologous to human CRIP proteins, which are highly expressed in mammals but whose function is not yet known.  exc-9 shows genetic interactions with the exc-1 and exc-5 genes, and EXC-9 binds to EXC-1 in a yeast two-hybrid assay.  Using canal-specific subcellular fluorescent markers, we are examining the effects of exc-9 mutation on the movement and persistence of endosomes, and their effects on shape and function of the excretory canals.