Figure 7. Redundancy models for the collective action of multiple neuropeptides which regulate C. elegans stress-induced sleep.

The neurosecretory ALA is required for stress-induced sleep. ALA transcribes multiple genes encoding neuropeptides, and we have shown that three neuropeptides enriched in ALA collectively regulate C. elegans stress-induced sleep. Given the non-overlapping expression pattern of these neuropeptides in other neurons, it is also possible that these neuropeptides act from neurons which have a minor role in regulating stress-induced sleep. In Model 1 each neuropeptide acts on a distinct neuron within a set of neurons that regulates behavior. In Model 2 each neuropeptide acts on the same neuron within a set of neurons that regulates behavior. The principles of Model 1 and 2 also apply at the receptor and behavioral level. For instance, each neuropeptide may act at a distinct receptor, or all the neuropeptides may act on the same receptor. In addition, strong inhibition of one behavior may inhibit all other behaviors and result in sleep, or there may be shut down of multiple behaviors simultaneously. We predict that these neuropeptides regulate C. elegans stress-induced sleep by some combination of Model 1 and 2 at the cellular, receptor, and behavioral level.