Worm Breeder's Gazette 12(4): 64 (October 1, 1992)
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.
We have been working on the control of the periodic activation of the defecation motor program. What factors determine that the defecation motor program is activated every 45 sec in well-fed adult worms? In part we have taken a genetic approach to answering this question. We have outlined our screen for defecation cycle period mutants (Dec) in recent C. elegans meeting abstracts. The mutants we have identified so far fall into several classes; Dec-s (short) mutants that activate the motor program faster than every 45 sec, Dec-l (long) mutants that have much longer intervals between defecations, Dec-v (variable) mutants that have cycle periods that vary, and finally the Dec-echo mutant which I will discuss in detail.
The" Echo" phenotype was originally described for the strain DR86 carrying daf-19 ( m86 )II, as an additional posterior body contraction following the normal motor program with a delay of about 10 seconds (Thomas, Genetics, 1990). We have recently determined that the echo phenotype does not map to the daf-19 locus but to an independent location in the unc-22 cluster of IV. We have designated this Echo allele sa200 . sa200 is completely recessive and it's phenotype is similar in trans to a deficiency of the locus, indicating that Echo may be the null phenotype.
Wild-type worms on plentiful food activate the motor program about every 45 sec with a standard deviation of less than 3 sec, as shown in the left panel of the figure. In the figure the occurrence of the motor program is indicated by the letters p, a, and x for each of the three steps of the complete motor program, posterior body contraction, anterior body contraction, and expulsion. Each part of the motor program is usually but not necessarily activated for each defecation. Each dot represents one second of elapsed time. The right panel shows the defecation phenotype of the mutant JT200 ( sa200 ).Following the normal motor program is a weaker and more variable version of the motor program that we have termed the Echo. The Echo cycle follows the principal cycle with a latency of 10-15 sec. The Echo cycle is much more likely to be missing a part of the motor program and the contraction of the muscles appears weaker. [See Figure 1]
JT200 animals also have an unusual phenotype in the absence of food. In the absence of food wild-type animals stop pumping their pharynx and cease defecating. After more than one hour off of food animals resume sporadic pumping of their pharynx but defecate very infrequently, on average less than once every 400s (n = 19 animals). In contrast after about 20 minutes off of food, JT200 animals resume defecating. The average cycle period is 145s (n=19 animals) and appears less periodic, but defecation is occurring much more frequently than in wild-type animals. Additionally, echos are seldom observed when JT200 activates the motor program off of food (see below).
We wondered whether food concentration affected the 10-15s delay between the principal cycle and the echo, or whether food concentration determined how often an echo occurred. We made a concentrated suspension of OP50 (A=.60 at OD600 ),which, when spread on agar plates had the consistency of a mature bacterial lawn. This was designated a 1x food preparation. We tested echo and N2 animals on 1 x food to confirm that cycle periodicity was the same as on normally grown food. We then tested animal's defecation behavior on dilutions of the 1x food stock. Based on the data in the Table, we conclude that the probability of an echo occurring is influenced by the food concentration while the delay from principal cycle is not. [See Figure 2]