The Lantern Vol. 18, No. 3, Spring 1950

• The Rise and Fall of Mr. Fluff • Thoughts by the Sea • Equality of Men • On Radio Comedians • After Hours • Rain • Morning • Escape from Fear • Book of Red • Poems by a Guy Named Mike • We are the People • Spirit Disrupted • Light • Sonnethttps://digitalcommons.ursinus.edu/lantern/1051/thumbnail.jp

Investigating the cell biological mechanisms regulated by the cellular prion protein

Transmissible spongiform encephalopathies (TSEs) are rare, uniformly fatal neurodegenerative disorders that can affect many mammalian species, including humans. A hallmark of these diseases is the conversion of cellular prion protein (PrPC) into an abnormally folded form. This misfolded PrPC is infectious, since it can provide a template for pathogenic conversion of PrPC in a new host. In addition to any toxicity of the misfolded protein, loss of normal PrPC function could be involved in the neurodegenerative processes. However, the physiological role of PrPC is still poorly understood and this project has aimed to address that lack of knowledge. Out of the many putative functions ascribed to PrPC, the most commonly proposed is that it protects cells from stress. In contrast, I have found that stable transfection of the prion protein gene into SH-SY5Y neuroblastoma cells increases cell death in response to serum removal from the culture medium. Following treatment with several chemical toxins, two out of four stably transfected clones did, generally, display greater viability than untransfected cells that do not express detectable levels of PrPC. However, knockdown of PrPC expression by RNA interference had no effect on this stress resistance, indicating that it may not have been mediated directly by PrPC. Given the lack of robust stress protection afforded by PrPC transfection, proteomic analyses of the cells were carried out to identify alternative processes that were perturbed as a result of PrPC expression. The results obtained suggested roles for PrPC in cytoskeletal organisation and cell cycle regulation. Various proteins involved in cytoskeletal organisation were confirmed by western blotting to be differentially expressed in some or all of the stably transfected clones. Additionally, the expression changes to proteins involved in cell cycle regulation resulted in slower proliferation of the clones compared with untransfected cells, a difference that was reduced following RNA interference-mediated knockdown of PrPC. Taken together, these data suggested that specific growth factor-activated pathways were differentially regulated in the stably transfected clones. One candidate pathway was nerve growth factor (NGF) signalling, which promotes neuronal survival and differentiation as well as regulating various processes outside of the nervous system. PrPC-transfection resulted in altered expression of receptors for NGF, suggesting that the stably transfected clones were, indeed, responding differently to NGF stimulation. However, the molecular mechanism responsible for these expression changes remains to be determined, since co-immunoprecipitation experiments did not identify any physical interactions between PrPC and the NGF receptors. Nonetheless, a role for PrPC in modulating NGF signalling has the potential to explain many of the diverse phenotypic observations in PrPC-null mice and might indicate that loss of PrPC function is an important part of TSE pathogenesis

Semicircular canal morphogenesis in the zebrafish inner ear requires the function of gpr126 (lauscher), an adhesion class G protein-coupled receptor gene.

Morphogenesis of the semicircular canal ducts in the vertebrate inner ear is a dramatic example of epithelial remodelling in the embryo, and failure of normal canal development results in vestibular dysfunction. In zebrafish and Xenopus, semicircular canal ducts develop when projections of epithelium, driven by extracellular matrix production, push into the otic vesicle and fuse to form pillars. We show that in the zebrafish, extracellular matrix gene expression is high during projection outgrowth and then rapidly downregulated after fusion. Enzymatic disruption of hyaluronan in the projections leads to their collapse and a failure to form pillars: as a result, the ears swell. We have cloned a zebrafish mutant, lauscher (lau), identified by its swollen ear phenotype. The primary defect in the ear is abnormal projection outgrowth and a failure of fusion to form the semicircular canal pillars. Otic expression of extracellular matrix components is highly disrupted: several genes fail to become downregulated and remain expressed at abnormally high levels into late larval stages. The lau mutations disrupt gpr126, an adhesion class G protein-coupled receptor gene. Expression of gpr126 is similar to that of sox10, an ear and neural crest marker, and is partially dependent on sox10 activity. Fusion of canal projections and downregulation of otic versican expression in a hypomorphic lau allele can be restored by cAMP agonists. We propose that Gpr126 acts through a cAMP-mediated pathway to control the outgrowth and adhesion of canal projections in the zebrafish ear via the regulation of extracellular matrix gene expression