Worm Breeder's Gazette 7(1): 95
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
Although the nuclei of cells associated with the C. elegans excretory system have been identified by Nomarski microscopy (Sulston and Horvitz, Devel. Biol. 56:110, 1977), no one seems to have gotten around to a careful look at the ultrastructure of these cells. Because the excretory gland cell may play some role in the control of molting, or more specifically in dauer larva formation, we decided to have a close look at its anatomy and its relationship to the other cells of the excretory system, in order to lay the groundwork for laser ablation experiments, as well as comparison of normal and mutant ultrastructure. Although several studies of excretory anatomy have been done in parasitic species, little is known about the physiology of these systems or what role associated gland cells may play in development, reproduction or behavior. In some species at least, the excretory system is almost certainly involved in osmoregulation. All C. elegans larval stages, including dauers, engage in excretory pumping (commonly known as tinkling). So far we haven't detected any filamentous muscle-like structures associated with the excretory duct, so pumping may be non-muscular. Instead, the normally collapsed duct may be periodically forced open by internal pressure from the excretory cells. The secretory-excretory system consists of four cells. (1) The terminal half of the cuticle-lined excretory duct is enclosed by a specialized hypodermal cell, the pore cell. (2) The duct cell surrounds the duct from the origin of the duct to the pore cell boundary. The duct cell contains an elaborate lamellar system which may function to increase the cell surface area at the duct for the purpose of resorption or other transport. (3) The large H-shaped excretory cell extends bilateral canals anteriorly and posteriorly nearly the entire length of the worm. The cell body contains an excretory sinus, a system of very small channels which joins the termini of the four excretory canals with the origin of the excretory duct. (4) A binucleate, A-shaped gland cell extends bilaterally symmetrical processes from cell bodies just behind the terminal bulb of the pharynx anteriorly to the nerve ring where the processes join and apparently receive synaptic input. The gland cell processes are also joined by a bridge across the anterior edge of the excretory cell body, where the gland cell, duct cell, and excretory cell are all joined at a desmosome-like dense plaque we call the secretory- excretory junction. A uniquely specialized portion of the gland cell membrane (an assembly of tubules in an electron-dense matrix similar to the porcelain screen on a Buchner funnel) connects the gland cell to the origin of the excretory duct directly adjacent to the point where the excretory sinus empties into the duct. In L2's, L4's and adults, at least, numerous secretory granules of varying electron- density are concentrated in the gland cell around the junction. Similar granules are associated with golgi complexes near the gland cell nuclei. Dauer larvae, however, totally (or almost totally) lack secretory granules. It is as if the secretory system is being completely reprogrammed in the dauer. This is true of starvation- induced dauers and pheromone-induced dauers. Starved L2's seem to have a reduced number of granules but do not share the striking alteration of glandular morphology exhibited by dauer larvae. L4 larvae which have recovered from the dauer stage regain the secretory morphology of well-fed L2's and adults. The portion of the gland cell where secretory granules are most concentrated stains intensely with paraldehyde-fuchsin (PAF). Only dauers and starved worms fail to stain. Thus, PAF staining appears to be correlated with a high concentration of secretory granules. Staining seems not to be correlated with molts. Laser ablation experiments in progress may yield some insights into cellular functions, particularly with regard to dauer larva formation.