Title: Prohibitin Homology Domain Proteins in Caenorhabditis elegans
Description: The PHB-d protein family is an evolutionarily ancient family of integral membrane proteins with members in all taxa that are involved in a wide variety of biological process but share several common molecular properties: oligomerization, detergent resistant membrane (DRM) association, and regulation of other proteins. To better understand the biological roles of the PHB-d gene family and provide a starting point for analysis of their individual functions, I determined the expression patterns of all of the uncharacterized PHB-d genes in the nematode C. elegans. All eight of the proteins similar to mammalian stomatin are detectably expressed in neurons. The specificity of expression varies from 34 neuron types that express sto-4 to only one that expresses sto- 3. STO-1 protein is localized to amphid sensory cilia and is needed for optimal chemotaxis to diacetyl. This phenotype is likely to affect chemotaxis mediated by the AWA sensory neurons. Involvement of PHB-d proteins in ! chemosensation may be conserved in mammals.

Two murine PHB-d genes are highly expressed in olfactory sensory neurons, but no olfactory phenotype has been described in mice lacking either gene. C. elegans senses gentle body touch via a mechanosensory channel complex that contains two Degenerin/Epithelial sodium channel (DEG/ENaC) subunits and two prohibitin homology domain (PHB-d) proteins. One of the PHB-d proteins (UNC-24) has a C-terminal sterol carrier protein 2 (SCP-2) domain and only a subtle mechanosensory abnormal (Mec) phenotype. The other PHB-d (MEC-2) is essential for channel function. I show here that unc-24 is needed for proper localization of MEC-2 to the channel complex, but that this function is unlikely to underlie the unc-24 phenotype. This result supports the hypothesis that PHB-d/SCP-2 proteins have a conserved role in localizing other PHB-d proteins and demonstrates that UNC-24 must have a second, unknown, role in mechanosensation. MEC-2 is embedded in the plasma membrane via a non-spanning hydrophobic hook. Mutation of a conserved proline (P134S) in the hydrophobic hook leads to complete touch insensitivity.

Mutation of the equivalent proline in human stomatin converts the hook to a transmembrane domain and expels the PHB-d and C-terminus of the protein. We show here that the P134S mutation has the same effect on MEC-2 topology in HEK293T cells. This result has implications for MEC-2 function because the P134S mutation has previously been shown to affect some but not all MEC-2 biochemical properties. The conserved proline is found in all C. elegans and human stomatins and its mutation in human podocin leads to kidney failure.