The worm integrates sensory information about its external environment and information regarding its biological disposition to produce a variety of probabilistic exploratory behaviors. In the presence of food, wild-type adult hermaphrodites alternate between two distinct exploratory behaviors known as roaming and dwelling (Fujiwara et al., 2002). During roaming, animals exhibit long bouts of forward locomotion and infrequent reversals, whereas dwelling behavior is characterized by short bouts of forward movements and frequent reversals. Wild-type animals typically spend the majority of their time in the roaming state, extensively exploring the bacterial lawn. We recently isolated a spontaneous mutant with specific defects in the regulation of exploratory behavior, such that adult hermaphrodites exhibit a severely restricted track pattern on a bacterial lawn, absent any apparent deficits in motor coordination or overall activity levels. This phenotype segregates as a single, recessive allele that we have designated
fs9. Notably, similar exploratory behavior phenotypes have been observed in animals with defective sensory cilia, particularly
che-2 (Fujiwara et al., 2002). Animals homozygous for
fs9, however, do not exhibit dye-filling defects or the small body size characteristic of
che-2 animals, suggesting that
fs9 does not disrupt the development or maintenance of cilia. Loss-of-function mutations in the cGMP-dependent protein kinase
egl-4 have been previously shown to completely suppress the
che-2 exploratory behavior phenotype (Fujiwara et al., 2002). Interestingly, the canonical
egl-4 allele
n478 only weakly suppresses the exploratory behavior phenotype of
fs9 animals, further suggesting that the gene defined by
fs9 may act downstream of, or in parallel to,
egl-4 to control exploratory behavior. We are currently attempting to identify the gene affected by
fs9, and have mapped the mutation to a small interval on LG V. Molecular characterization of this gene is likely to yield important insights into the genetic regulation of exploratory behavior in the worm. This work is supported by NIMH grant T32 MH065181: Multidisciplinary Training in Developmental Neuroscience. <sub>1Fujiwara M, Sengupta P, McIntire SL (2002) Regulation of body size and behavioral state of C. elegans by sensory perception and the EGL-4 cGMP-dependent protein kinase. Neuron 36(6):1091-102</sub>.