NaCl is essential for homeostasis and physiological functions in many organisms. However, the molecular mechanism of NaCl detection is not well known. In mammals, the epithelial Na+ channel (ENaC) and the transient receptor potential ion channel of the vanilloid type 1 (TRPV1) have been shown to be involved in NaCl detection. Previous studies in C. elegans identified five genes involved in NaCl chemoattraction. These are
tax-2 and
tax-4 (cyclic nucleotide gated (CNG) channel subunits),
tax-6 and
cnb-1 (calcineurin A and B subunits) and
ncs-1 (neuronal calcium sensor). Analysis of these mutants in our assay, in which we exposed the animals to a very steep NaCl gradient, showed reduced chemotaxis to NaCl. However we found that these mutants still showed significant attraction at higher NaCl concentrations. By analyzing the behaviour of double mutants, we found that chemotaxis to NaCl involves two genetic pathways. The first pathway involves two mitogen activated protein (MAP) kinases,
nsy-1 and
sek-1, and three genes that have been previously characterized,
tax-2,
tax-4 and
tax-6. The second pathway involves
tax-2, another CNG channel subunit,
cng-3, the G Your browser may not support display of this image. protein
odr-3, the TRPV channel subunit
osm-9 and the guanylate cyclase
gcy-35. We used cell specific rescue of the mutant genes, laser ablation of specific neurons and neuronal calcium imaging to find out where in the neuronal circuit of C. elegans these genes function. Thus far, the involvement of the main salt sensing neurons, ASE, has been confirmed. In addition, we found that the ADF neurons also play a role. We are currently performing a synthetic genetic screen to identify additional genes that play a role in NaCl chemotaxis. We are using
odr-3 mutants to find mutants that affect the
nsy-1/sek-1/tax-2/tax-4/tax-6 NaCl chemotaxis pathway.