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.

The C. elegans Secretory-excretory System

K. Nelson, P. Albert, D. Riddle

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.