Polycystic Kidney Disease is a genetic disorder affecting 1 in 500 people, in which the tubular nephrons swell to large fluid-filled cysts. The most common forms of the disease result from dominant mutations in either of two genes:
pkd1 and
pkd2. We are studying
pkd-2, the C. elegans homologue of human
pkd2. These genes encode novel members of the TRP family of divalent cation channels; the homology from worm to human is especially strong in the 6 transmembrane domains and the presumptive gating region between the first and second transmembrane domains. Our current research will determine whether the nematode protein functions as a calcium channel. PKD-2 regulates neural function in the C. elegans male, such that the mutant male either fails to recognize the hermaphrodite vulva or loses contact while attempting to mate (Barr et al., Curr. Biol. '01). We find that
pkd-2 worms express an additional mutant phenotype: A population of mutant animals disperses rapidly on a lawn compared to wild-type worms. This phenotype may be mediated by frequent loss of
pkd-2 between males and hermaphrodites, and loss of expression of
pkd-2 in the sensory cephalic neurons. We are currently determining whether cloned human
pkd2 cDNA (graciously supplied from the Somlo laboratory) can rescue the mutant C. elegans phenotype. We are also constructing chimeric human-nematode
pkd2 genes to allow us to determine which regions of the protein might be responsible for phenotype rescue. We have cloned nematode
pkd-2 cDNA, and expressed it in various mammalian cell lines. The single-channel electrophysiological properties of this channel in isolated membrane vesicles will be investigated via black lipid membrane techniques. Finally, we have mutagenized
pkd-2 mutant worms in an attempt to discover alternative pathways that suppress the
pkd-2 phenotype. We have isolated several lines that exhibit partial rescue of wild-type dispersal behaviour, and subsequently found that their mating behaviour is also restored. We are using genetic markers, including single nucleotide polymorphisms, to map the putative suppressor genes associated with phenotypic rescue.