Worm Breeder's Gazette 6(1): 25

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.

A Pheremone for Dauer Larva Formation?

J.W. Golden, D.L. Riddle

High population density influences dauer larva formation as 
demonstrated by growth of nematodes to high density either in liquid 
medium, on enriched agar plates or on egg white plates.  Dauer larvae 
are produced under these conditions by wild-type animals prior to 
exhaustion of the food supply.  Our recent work, based on the 
observations of Cassada and Russell (Develop.  Biol.  46:326,175), has 
shown that the medium from such cultures contains a stable, nematode-
produced substance of low molecular weight which both promotes dauer 
larva formation and inhibits exit from the dauer stage.  We have named 
the substance DRIF, for dauer recovery inhibition factor.  DRIF can be 
detected in starved or non-starved liquid culture media, and it can be 
extracted from worms washed off of non-starved NGM plates.
A dauer-recovery bioassay for DRIF has been developed which allows 
its detection at a 1/120 dilution from starved liquid culture media.  
DRIF's effect on both dauer larva formation and recovery is in 
competition with the food supply and can be overridden by an abundance 
of food.  E. coli cells in a concentration greater than 2x10+E9/ml 
overcome inhibition of dauer recovery by DRIF at starved media 
concentration.  Since the bacteria do not degrade DRIF, we conclude 
that bacteria and DRIF provide competitive chemosensory signals.  DRIF 
is produced by C.  elegans var.  Bristol and Bergerac, C.  briggsae, 
and all of the dauer-defective mutants assayed so far.  It cannot be 
found in liquid culture media which has not been inoculated with worms,
nor can it be found in starved liquid cultures of Panagrellus 
redivivus.  (Panagrellus does not make dauers.)
DRIF has a molecular weight of less than 1000 daltons and has a net 
negative charge at pH7.  It is nonvolatile and cannot be extracted 
with ether or chloroform:methanol (2:1).  It is stable to various 
treatments including autoclaving, treatment with acid or base, and 
digestion with protease, DNAase, RNAase, and phosphodiesterase.  We 
are in the process of purifying DRIF so that its structural and 
biological properties may be more thoroughly studied.
Our hypothesis is that DRIF may be the environmental cue which 
triggers dauer formation in crowded cultures.  Our liquid cultures 
reach a density more than 10-fold greater than that reached by 
populations on NGM plates.  As reported by Peg Swanson in the last 
Newsletter, dauer-defective mutant phenotypes suggest that the 
response to starvation is at least partially distinct from the 
response to high population density.  Some mutants, e.g.  CB1377 daf-6,
do not form dauers in liquid or on plates, while other dauer-
defective mutants, e.g.  CB1376 (daf-3), form many dauers when grown 
to starvation in liquid.  Thus, CB1377 is blocked in both responses, 
while CB1376 is blocked in the starvation response, but nearly normal 
in the response to high population density.  It is conceivable that 
different sensory neurons could mediate the responses to different 
Several laboratories have observed independently that large numbers 
of dauers form in cultures grown on egg-white plates.  Interestingly, 
worms grown on such plates 'phenocopy' dauer-constitutive mutants in 
that adults retain eggs, and the dauers formed are large (well-fed).  
Since chicken egg-white itself does not contain DRIF activity, we 
presume that dauer formation on egg plates is due to nematode DRIF 
production, perhaps combined with a declining food supply.  It is 
difficult to determine when an egg white plate is 'starved' because 
the bacterial food is not visible in all that mess.  The worms will 
not grow on sterile egg white plates.