The cyclic AMP-response element binding protein CREB plays a central role in long-term memory in Aplysia, Drosophila and mice. We characterized the C. elegans and C. briggsae CREB genes (
crb-1) and found that the encoded proteins are 85% identical. The DNA-binding bZIP domain and cAMP-dependent kinase site, as defined in the mammalian and Drosophila CREB family members, are highly conserved in the nematode proteins. The C. elegans
crb-1 gene has two alternatively-spliced isoforms. Our immunohistochemical studies indicate that CRB-1 is ubiquitously expressed throughout development and in adults. CRB-1 can bind to cyclic AMP-response element (CRE) sites and can be phosophorylated by cAMP-dependent protein kinase (PKA) in vitro. To determine the function of
crb-1 in the worm, we isolated three deletion alleles of
crb-1 from a chemical deletion library. Two are predicted to cause early truncations, and the third deletes part of the bZIP domain. No CRB-1 protein is detected by western blot analysis of these three mutant strains, suggesting that all three are null alleles.
crb-1 mutants are viable and show no obvious abnormalities in brood size, locomotion, mechanosensation, chemotaxis or thermotaxis. However,
crb-1 mutants tend to accumulate at the edge of the bacterial lawn (bordering) and form clumps of animals. In addition, mutations in
crb-1 confer a dauer-constitutive phenotype (Daf-c) at 27C but not at 25C. The Daf-c phenotype of
crb-1 animals is suppressed by mutations in
daf-16 and
daf-12 but not by mutations in
daf-5. This finding suggests that
crb-1 acts in the DAF-2 insulin receptor-like signaling pathway. A similar role has been suggested for
unc-31 and
unc-64,1 which are implicated in synaptic vesicle release. Double mutants between
crb-1 and either
unc-31 or
unc-64 show a strongly enhanced Daf-c phenotype at 25C as has been shown for
unc-31;
unc-64 double mutants.1 This synergy suggests that mutations in
crb-1, like mutations in
unc-31 and
unc-64, impair synaptic function. Unlike
unc-31 or
unc-64 mutants,
crb-1 mutants do not have an increased life span. We are further investigating the role of
crb-1 in synaptic transmission, dauer formation, and behavior. 1. Ailion, M., Inoue, T., Weaver, C.I., Holdcraft, R.W. and J.H. Thomas, (1999) PNAS 96: 7394-7397.