BGU Physics Department

Colloquium, Dec. 16th, 2010

"So, do worms sleep?" and other questions that may have never crossed your mind

David Biron, Department of Physics, University of Chicago

Despite much progress in our understanding of C. elegans locomotion and navigation, little is
known about the regulation of the absence of movement. Yet behavioral quiescent states are
universal to the animal world, with the most famous and mysterious of these being sleep. In a
famous example of studying a sleep-like behavior in a phylogenetically ancient model organism,
Seymour Benzer - physicists, biologists and one of the founders of the field of molecular biology
of behavior - studied the cycles of quiescence of the fruit fly Drosophila. He showed that the
period gene was a key regulator of the circadian clock, which was found to have a role in
regulating sleep in mammals. Recently, additional pathways were implicated in regulating sleeplike
behavior in fruit flies and sleep in mice, rabbits and hamsters: Epidermal Growth Factor
(EGF) signaling and cyclic-Adenosine MonoPhosphate (cAMP) signaling.
The roundworm C. elegans is in many ways a simpler model organism than the fruit fly. It
has only 302 neurons (the connections of which have been anatomically mapped), a short life
cycle and an optically transparent body. The worm develops through four larval stages before it
reaches adulthood. At the end of each of these stages it exhibits a quiescent behavior called
lethargus. David Raizen et al. recently demonstrated that lethargus bears behavioral similarities
to sleep, such as reversibility (the worms "wake up"), sensory gating (an elevated threshold for
responding to sensory stimuli) and homeostatic control (following deprivation, lethargus is
resumed faster and "deeper"). Curiously, lethargus is also phase-locked with cycles in the
expression of the worms period homologous gene. Moreover, EGF and cAMP signaling both
appear to have roles in regulating lethargus that resemble their regulation of similar behaviors in
flies and mammals. Taken together, these observations suggest a possible ~6x108 year-old
genetic link between these phenomena.
I will discuss the opportunities, challenges and risks of studying a sleep-like behavior using
C. elegans as a model system, and present preliminary results from our behavioral analysis. Time
permitting, I will discuss some tools and ideas that physics can bring to the study of this
everyday natural phenomenon.