David M Raizen et al. (2005) International Worm Meeting "Characterization of behavioral quiescence in wild-type and egl-4"

David M Raizen, Meera Sundaram, Allan I Pack, Matthew Maycock

[International Worm Meeting, 2005]

In mammals, periods of quiescence usually correspond to sleep, and are controlled by circadian and homeostatic processes. Behavioral quiescence in Drosophila is also controlled by these two processes and by some of the neurochemicals that function in mammalian sleep, suggesting that the evolution of sleep is ancient. The timing of sleep maintains a constant phase relationship with the timing of expression of the circadian protein PERIOD. The purpose of sleep is unknown. Locomotion of C. elegans has been noted to stop only during the lethargus periods, which precede ecdysis. The timing of lethargus maintains a constant phase relationship with expression of the PERIOD orthologue LIN-42 (Jeon et al '99). We have been measuring the quiescence associated with lethargus by observing single worms from the late L3 until adulthood. Using a digital imaging approach, we define quiescence as a body movement of less than 10 microns in 10 seconds. We found that N2 worms have periods of quiescence only during the lethargus periods. When mechanically stimulated at various times after the onset of lethargus, the animal is able to move normally, indicating that this quiescent state is reversible, and therefore under nervous system regulation. When the animal is kept moving continuously for over 30 minutes during lethargus but not outside of lethargus, it becomes increasingly difficult to arouse, suggesting that the quiescence is important for the animal and cannot be bypassed. We are currently testing for homeostatic regulation of this behavior to address the idea that lethargus is a sleep-like state. The gene defined by eat-7(ad450sd) appears to regulate quiescent behavior. In ad450sd mutants, the intervals between lethargus periods are unchanged but there is an increase in quiescence during lethargus. ad450sd also has periods of quiescence outside lethargus. When mechanically stimulated or when starved, ad450sd mutants move normally, indicating that the increased behavioral quiescence is not explained by an inability to move well. Body size, life span, roaming behaviors, and intestinal darkness are all decreased in ad450sd. We found that ad450sd is a hypermorphic allele of the gene egl-4, which encodes a cGMP-dependent protein kinase. We will describe our characterization of 6 mutants that suppress some or all of the ad450sd phenotypes.