egl-4 acts through a transforming growth factor-beta/SMAD pathway in Caenorhabditis elegans to regulate multiple neuronal circuits in response to sensory cues

Sensory cues regulate several aspects of behavior and development in Caenor habditis elegans, including entry into and exit from an alternative develop mental stage called the dauer larva. Three parallel pathways, including a T GF-P-like pathway, regulate dauer formation. The mechanisms by which the ac tivities of these pathways are regulated by sensory signals are largely unk nown. The gene egl-4 was initially identified based on its egg-laying defec ts. We show here that egl-4 has many pleiotropies, including defects in che mosensory behavior, body size, synaptic transmission, and dauer formation. Our results are consistent with a role for egl-4 in relaying sensory cues t o multiple behavioral and developmental circuits in C. elegans. By epistasi s analysis, we also place egl-4 in the TGF-P-like branch and show that a SM AD gene functions downstream of egl-4 in multiple egl-4-regulated pathways, including chemosensation.