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Regulation of a periodic motor program in C. elegans
1University of Washington, Department of Genetics, Seattle 98195.
Summary
The defecation cycle in C. elegans is controlled by an internal clock, likely a neuronal pattern generator, independent of the motor program itself. Feeding behavior modulates this rhythm, with mutations affecting food response altering defecation timing.
Area of Science:
- Neuroscience
- Behavioral Biology
- Genetics
Background:
- The nematode *Caenorhabditis elegans* exhibits a regular defecation rhythm, occurring approximately every 45 seconds in well-fed wild-type individuals.
- This rhythmic behavior is mediated by a three-part motor program, with individual worms maintaining a precise cycle (SD ≈ 3 seconds).
Purpose of the Study:
- To investigate the underlying mechanisms controlling the *C. elegans* defecation rhythm.
- To determine if the defecation cycle is governed by an endogenous clock and its relationship with feeding behavior and motor program execution.
Main Methods:
- Behavioral analysis of wild-type and mutant *C. elegans* under various feeding conditions.
- Neuronal circuit stimulation and laser ablation experiments to assess the role of specific neurons.
- Genetic analysis of mutations affecting defecation, including the *dec-8(sa200)* mutant.
Main Results:
- Evidence suggests the defecation cycle is controlled by an endogenous clock, likely a neuronal pattern generator, capable of being reset by sensory stimuli (e.g., light touch).
- The defecation rhythm persists even when feeding is interrupted, indicating the clock runs independently of motor program expression.
- Mutations affecting the motor program itself did not alter the rhythm, supporting the independence of timing control.
- Food availability strongly modulates the rhythm; absence of food reduces activation, while food dilution lengthens the cycle period.
- The *dec-8(sa200)* mutant activates the motor program without food, and exhibits tandem activations with food, suggesting altered food-response pathways.
Conclusions:
- The *C. elegans* defecation rhythm is primarily regulated by an internal neuronal clock, distinct from the motor execution pathway.
- Feeding acts as a crucial modulator of this rhythm, influencing its precision and frequency.
- The *dec-8* mutation provides insights into the genetic control of integrating feeding cues with the defecation timing mechanism.