Advisory Committee Chair
Advisory Committee Members
Date of Award
Degree Name by School
Doctor of Philosophy (PhD) Heersink School of Medicine
Nephronophthisis (NPHP) is a ciliopathy with diverse clinical features likely caused by genetic modifiers. To identify NPHP modifiers, a screen was conducted on nphp-4(tm925) mutant C. elegans to reveal mutations that exacerbate the NPHP ciliary defects. Ten loci were generated, five of which have now been identified. Three are mutations in ciliopathy genes mks-1, mks-2, and mks-5. The fourth allele (yhw66) is a missense mutation (S316F) in OSM-3, a kinesin required for cilia distal segment assembly. As in osm-3 null mutants, nphp-4(tm925);osm-3(yhw66) mutants lack distal segments, are dye-filing defective (Dyf), and have osmotic avoidance defects (OSM). The osm-3(yhw66) mutant alone has no overt cilia phenotype but do have reduced IFT rates. To evaluate the possibility S316F is a phosphorylation site, we compared the localization and function of phospho-null OSM-3(S316F), phospho-mimetic OSM-3(S316D), and wild type OSM-3. OSM-3(S316F) is enriched at the cilia base compared to wild type OSM-3. In contrast, OSM-3(S316D) accumulates in the cilia distal tip. While OSM-3(S316F) rescues all phenotypes in osm-3(mn357) nulls and OSM-3(S316D) restores distal cilia segments, OSM-3(S316D) does not rescue the Dyf phenotype with or without NPHP-4. Thus, there are NPHP-4 dependent and independent phenotypes associated with these OSM-3 mutations. These data reveal that NPHP-4 can exert regulatory influences on trafficking and function of a ciliary kinesin. The fifth allele from the screen was cca-1, a T-type calcium channel. The genetic interaction between cca-1 and nphp-4 is not critical for building the cilia but is necessary to maintain the cilium and affects its localization in an NPHP-4 dependent manner. Without this interaction calcium signaling and adaptation responses in the AWC neuron is impaired. Moreover, the data suggest that the human OSM-3 (Kif17) and CCA-1 (CACNA1I) homologs are candidate modifying locus affecting disease penetrance or expressivity in NPHP patients.
Landis, Dawn, "An nphp-4 enhancer mutagenesis screen for modifiers of cilia phenotypes reveals novel MKS alleles, uncovers, a specific genetic interaction between osm-3 and nphp-4, and a novel ciliary calcium channel." (2015). All ETDs from UAB. 2214.