Worm Breeder's Gazette 10(2): 41

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.

Sensory Cells for an Endogenous C. elegans Avoidance Factor

Jim Thomas and Bob Horvitz

When a worm encounters certain noxious conditions with its nose it 
backs up (see WBG 10-1, p.  89 for how we assay this behavior).  In 
the process of testing various chemicals and extracts for activity in 
the avoidance assay, we found that C.  elegans itself makes an 
avoidance factor which produces a response that is very similar to 
osmotic avoidance.  This avoidance response is not due to any of the 
known avoidance chemicals.
We have killed various cells with a laser to define which sensory 
neurons are required for the avoidance factor (Afa) response.  The 
source of avoidance factor for the tests is an ultrafiltered crude 
lysate of C.  elegans.  When the amphid sheath is killed animals 
become Afa nonresponsive, suggesting that the amphid sensillum is 
required for Afa detection.  When the amphid sensory cell ASH is 
killed animals are less sensitive, and when ASH and ADL are killed 
together animals are nonresponsive to Afa.  When ADL is killed alone 
the animals respond normally.  Interestingly, the primary Afa sensor, 
ASH, is the same cell that is the primary osmotic avoidance sensor (
WBG 10-1).  Both ASH and ADL have synaptic wiring (White, et al.  1986.
Phil.  Trans.  Royal Soc.  London 314: 1-340) consistent with being 
avoidance sensory neurons, because they are unique among amphidial 
neurons in having synaptic output to AVA and AVD (the interneurons 
that drive backward movement, Chalfie, et al.  1984.  J.  Neurosci.  
5: 956-964).  One model for Afa avoidance is that ADL and ASH act by 
directly activating AVA and AVD, thus causing the avoidance behavior.  
This model can be tested by killing other cells to which ADL and ASH 
synapse, and by killing AVA and AVD.
The C.  elegans avoidance factor is not yet well characterized.  It 
is not excreted into the medium, but is released upon boiling or 
sonication of worms.  It is made at about normal levels by daf-22(m130)
animals, which make no dauer pheromone.  It is heat stable and passes 
through a filter with a 10,000 dalton exclusion limit.  No avoidance 
factor is found in E.  coli or Drosophila melanogaster larva extracts, 
but a factor that C.  elegans avoids is found in soil nematodes of the 
genera Pelodera and Pellioditis.  A possible function for avoidance 
factor is to signal the presence of a feeding predator of nematodes.  
Most such predators eat nematodes by puncturing their cuticle with a 
stylet or teeth and pumping up the insides.  Other nematodes could 
detect and avoid the active predator by sensing some chemical(s) 
released from broken worms.  A single adult C.  elegans exploded on a 
plate using a glass needle causes a rapid (within one minute) and 
strong (maximum radius about 1 mm from the victim) avoidance responses 
in nearby worms.