Negative regulation and gain control of sensory neurons by the C. elegans calcineurin TAX-6. 
Animals sense and adapt to variable environments by regulating appropriate sensory signal transduction pathways.  Here, we show that calcineurin plays a key role in regulating the gain of sensory neuron responsiveness across multiple modalities.  C. elegans animals bearing a loss-of-function mutation in TAX-6, a calcineurin A subunit, exhibit pleiotropic abnormalities, including many aberrant sensory behaviors.  The tax-6 mutant defect in thermosensation is consistent with hyperactivation of the AFD thermosensory neurons.  Conversely, constitutive activation of TAX-6 causes a behavioral phenotype consistent with inactivation of AFD neurons.  In olfactory neurons, the impaired olfactory response of tax-6 mutants to an AWC-sensed odorant is caused by hyperadaptation, which is suppressible by a mutation causing defective olfactory adaptation.  Taken together, our results suggest that stimulus-evoked calcium entry activates calcineurin, which in turn negatively regulates multiple aspects of sensory signaling.