C. elegans responds to adverse environmental conditions by arresting development as a dauer larva. A primary signal triggering dauer entry is secreted dauer pheromone. We and others showed that exposure to crude dauer pheromone alters the expression of a subset of putative GPCR genes in the ASI chemosensory neurons (Nolan et al., 2002; Peckol et al., 1999). We have now shown that similar to crude dauer pheromone, three chemically synthesized dauer pheromone components (Jeong et al., 2005 and see abstract by Butcher et al) all reversibly repress expression of the
str-3 chemoreceptor gene in the ASI neurons, but to varying degrees that correspond to their relative potencies in inducing dauer formation. To identify the signaling pathways and genes required for this pheromone-mediated gene regulation, we performed a forward genetic screen as well as a candidate gene search. Mutations in a putative GPCR gene severely compromised the ability of pheromone to repress
str-3 gene expression. Moreover, animals mutant for this GPCR gene also exhibited defects in the ability to form dauers upon pheromone exposure, suggesting that this GPCR may act as a dauer pheromone receptor. This GPCR gene is expressed primarily in the ASK chemosensory neurons, and consistent with its function as a putative pheromone receptor, the protein is localized exclusively to the ciliary endings. Currently we are further confirming the functions of this GPCR using in vivo imaging, heterologous expression systems, and pheromone binding assays. We also identified additional components of the pheromone signaling pathway. The ASK-expressed
gpa-3 G protein gene has previously been implicated in dauer formation (Zwaal et al., 1997). We found that
gpa-3(gof) mutations can suppress the GPCR signaling defects, and that moreover, lof mutations in
gpa-3 also result in a loss in pheromone-mediated signaling. We also identified
cmk-1 (CaMKI) and
ckk-1 (CaMKK) as genes that are required to repress
str-3 expression upon pheromone exposure. In addition, we showed that the
crh-1 CREB transcription factor is required to promote
str-3 expression even in the absence of pheromone. Thus, the CAMK cascade may act to inhibit CRH-1 function upon pheromone exposure. Unexpectedly, CMK-1 and CRH-1 appear to act cell non-autonomously in the ASE and AWC chemosensory neurons to regulate
str-3 expression in the ASI neurons, implicating a complex intracellular signaling network that mediates the effects of pheromone signaling.