Figure 5.

Model for chemosensory receptor regulation. Pheromone suppresses expression of srd-1, str-2, and str-3 in ASI. Sensory activity is required for srd-1 expression. Under standard conditions, ASI expression of srd-1 and str-3 is high, whereas str-2 expression in ASI is suppressed by endogenous pheromone levels. As pheromone concentrations increase, expression of all three receptors decreases, and if harsh conditions persist, dauer development occurs. One consequence of dauer development is the retraction of the ASI cilia from the pore, relieving pheromone repression. Although this derepression is sufficient for str-2 and str-3 to be expressed, the reduction in ASI activity prevents expression of srd-1.