Worm Breeder's Gazette 13(2): 53 (February 1, 1994)
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.
Only two neuron types are known to be essential- the pharyngeal motor neuron M4 ,which worms need for swallowing bacteria (Cell 51: 1071-1078) and the extrapharyngeal pair of CAN neurons (WBG 5(1): 19). I recently found conditions under which some M4 -worms survive and become fertile adults: growth on E coli HB101 ,which produces a liquid lawn that is easy to eat, and depolarization of pharyngeal muscle membranes, either with an eat-6 mutation (see article by Wayne Davis in this WBG) or with the acetylcholine agonist arecoline.
Hall and Hedgecock (Cell 65: 837-847) isolated a probable unc-104 null mutation, rh142 ,by noncomplementation screening. Only 10-20% of dpy-10 ( e128 ) unc-104 ( rh142 )worms became fertile adults, and they could not be used to found a strain. Hall and Hedgecock proposed that 80-90% of the worms were inviable because they lacked most or all functional synapses. Thinking that the inviability of unc-104 mutants might be caused in part by failure of M4 øneuromuscular transmission, I tested if unc-104 worms would have improved viability on HB101 .I separated unc-104 ( rh142 )from dpy-10 ( e128 )and tested unc-104 ( rh142 )homozygotes for growth. The best conditions were related to those for M4 øviability, but not identical:
10 mM serotonin dissolved in agar.
Plates recently seeded with E coli HB101 .
2 ml mineral oil placed on plate.
The mineral oil prevents the plate from drying out during the weeks required for the worms to grow. Serotonin was not necessary, but accelerated growth, presumably because it stimulates pumping. 1 mM arecoline completely prevented growth. This was not entirely surprising, since worms in which all pharyngeal neurons except M4 have been killed are arrested by concentrations of arecoline that have little effect on intact worms. Under the above conditions 20/20 unc-104 ( rh142 )progeny of unc-104 ( rh142 )/ dpy-10 unc-52 mnC1 mothers became fertile adults within 8 days. The plate grew to starvation in 34 days, and was used to found a strain. unc-104 ( rh142 )survival appears to be better than that of M4 øwild-type worms, although I have not made the comparison under identical conditions. Moreover, unc-104 ( rh142 )adults consistently had defecation cycles about 1 min long with coordinated pBoc, Exp, and at least in some cases aBoc phases, although the P-A-X motor program was skipped in occasional cycles. Electropharyngeograms recorded from these adults showed evidence of weak (and not entirely convincing) neuromuscular transmission by the inhibitory motor neuron M3 .Together these results, although not definite, suggest that there is still some synaptic transmission in unc-104 ( rh142 )mutants.