The cyclic AMP-response element binding protein CREB plays a central role in long-term memory in Aplysia, Drosophila and mice. C. elegans has a single CREB-homologous gene,
crh-1. We characterized the C. elegans and C. briggsae
crh-1 genes and found that the
crh-1 gene contains four alternative promoters that give rise to four different CRH-1 isoforms. All CRH-1 isoforms contain a C- terminal DNA-binding bZIP domain; two isoforms contain a N-terminal cAMP-dependent kinase site. The bZIP domain and cAMP-dependent kinase site share high similarity with the respective domains in the Aplysia, Drosophila and mammalian CREB family members. CRH-1 can bind to cyclic AMP- response element (CRE) sites and can be phosophorylated by cAMP-dependent protein kinase (PKA) and Calmodulin-dependent protein kinase II (CaMKII) in vitro. Immunohistochemistry with an antibody that recognizes all four CRH-1 isoforms shows that CRH-1 is localized to nuclei and is ubiquitously expressed throughout development. To determine
crh-1 function, we isolated three
crh-1 deletion. Western blot analysis shows that two deletion alleles,
crh-1(
n3450) and
crh-1(
n3451), eliminate the expression of the two CRH-1 isoforms that contain the cAMP-dependent kinase site. A third deletion allele,
crh-1(
n3315), eliminates the expression of all CRH-1 isoforms indicating that
crh-1(
n3315) is a null allele. All
crh-1 mutants are viable and show no obvious abnormalities in brood size, locomotion, mechanosensation, chemotaxis or thermotaxis. However,
crh-1 mutants tend to form clumps of animals and burrow into the agar, reminiscent of wild-type worms after food has been exhausted. In addition, we found that
crh-1 mutants are dauer-constitutive (Daf-c) at 27C but not at 25C. Many mutants that have a similar Daf-c phenotype at 27C, like
unc-3,
unc-31,
unc-64, have a synthetic Daf- c phenotype at 25C in double mutant combinations1. Double mutants between
crh-1 and either
unc-31 or
unc-64, but not
unc-3, show a strongly enhanced Daf-c phenotype at 25C. This observation suggests that
crh-1 and
unc-3 affect similar aspects of dauer formation. The decision to undergo dauer development is made in part by regulating the expression of the transforming growth factor (TGF)-beta homolog DAF-7 in the ASI chemosensory neurons in response to dauer pheromone, food availability, and temperature.
unc-3 encodes a transcription factor that is expressed in the ASI neurons and has been suggested to regulate the expression of
daf-72. The expression of a
daf-7::gfp reporter is strongly reduced in
crh-1 mutants, indicating that
crh-1 is part of a sensory signal transduction cascade that regulates
daf-7 expression. Interestingly,
daf-7::gfp expression is also strongly reduced in
tph-1 mutants which are defective in serotonin biosynthesis3. Serotonin modulates many behaviors of the worm in response to food. Our data suggest that
crh-1 mutants have defects in food sensation, and we hypothesize that
crh-1 functions downstream of serotonin in the long-term assessment of food availability.