All ETDs from UAB

Advisory Committee Chair

Bradley K Yoder

Advisory Committee Members

Scott Wilson

Kai Jiao

John L Hartman

Bradley K Yoder

Michael A Miller

Document Type

Dissertation

Date of Award

2011

Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine

Abstract

Primary cilia are antenna-like organelles that extend from the surface of almost all mammalian cell types. They regulate many signaling pathways and sense physical and chemical changes in the extracellular environment. Defects in primary cilia cause several human disorders of different severity collectively called ciliopathies, including nephronophthisis (NPHP), Joubert syndrome (JBTS), and Meckel-Gruber syndrome (MKS). Numerous MKS, JBTS and NPHP genes have been identified but in most cases of these ciliopathies the genetic defect is unknown. Despite the fact that NPHP, JBTS and MKS patients present with distinct clinical features, they have mutations in identical genes. This can be explained by different nature of mutations in these genes, genetic interactions with mutations in other cilia-associated genes and individual's genetic background influence. This is supported by data in the nematode C. elegans showing that simultaneous mutations in nphp and mks genes cause more severe cilia defects than mutations in only a nphp or mks gene. Here, the C. elegans model system was utilized to study nphp-4 genetic interactions. First, we analyzed the pathogenicity of eight human NPHP4 missense mutations in the worm homolog. We show that the majority of these mutations produce cilia defective phenotypes. Interestingly, despite the recessive inheritance of NPHP, some of the nphp-4 mutations where able to enhance mks phenotypes being while in heterozygous state. Second, we performed a chemical mutagenesis screen to find mutations in novel genes that interact with the nphp-4(tm925) null mutation to produce synthetic cilia defects and isolated nine independent loci. We identified mutations in the mks-5 and osm-3 genes that produced a nphp-4 dependent cilia phenotype. Since the other seven loci from the screen do not map to locations of known MKS/NPHP genes, their subsequent identification will likely provide novel candidates for human cilia related disorders. Overall these data expand our knowledge of genetic interactions in ciliopathies and further establishes C. elegans as a model to study these diseases.

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