WNK kinases comprise a small group of unique serine/threonine protein kinases conserved among multicellular organisms. Mutations in human WNK1 and WNK4 cause pseudohypoaldosteronism type II (PHA-II) disease, which is an autosomal-dominant illness featuring salt-dependent hypertension with hyperkalemia in human. Recent findings showed that WNKs phosphorylate and activate SPAK/OSR kinase, which in turn phosphorylates various ion channels such as NKCC, NCC and KCC. However, neither genetic nor physiological evidence of these relationships has been reported. The nematode Caenorhabditis elegans has
wnk-1 and
gck-3 genes, encoding homolog of WNK and SPAK, respectively. Biochemical analysis revealed that WNK-1 interacts with and phosphorylates GCK-3 in vitro. We constructed
wnk-1 deletion mutants and found that
wnk-1 is required for the tubular formation of excretory canals that regulate osmoregulation and waste elimination, analogous to the renal organs of higher animals. In addition,
gck-3 deletion mutants also exhibit abnormal excretory canal morphology similar to
wnk-1 mutants. These results suggest that WNK-1 controls the excretory canal morphogenesis by regulating GCK-3. Furthermore, animals defective in
wnk-1 are arrested at L1 or L2 larval stages, whose phenotype is not observed in
gck-3 mutants. To identify components functioning downstream of
wnk-1, we screened suppressor mutants of the
wnk-1 larval arrest phenotype. We isolated six suppressor mutants, two of them are dominant and others are recessive. One recessive suppressor mutation,
km61, was mapped on the middle region of LGIV. Further results will be presented in this meeting.