Lily Paemka and Joshua Fletcher will Present Their Research on August 8, 2013
Lily Paemka’s Abstract:
PRICKLE1 interaction with SYNAPSIN I reveals a role in Autism Spectrum Disorders
The frequent comorbidity of Autism Spectrum Disorders (ASDs) with epilepsy suggests a shared underlying genetic susceptibility; and several genes, when mutated, can contribute to both disorders. Recently, PRICKLE1 missense mutations were found to segregate with ASD, however the mechanism by which mutations in this gene might contribute to ASD is unknown. To elucidate the role of PRICKLE1 in ASDs, we carried out studies in Prickle1+/- mice and Drosophila, yeast, and neuronal cell lines. We show that mice with Prickle1 mutations exhibit ASD-like behaviors. To find proteins that interact with PRICKLE1 in the central nervous system, we performed a yeast two-hybrid screen with a human brain cDNA library and isolated a peptide with homology to SYNAPSIN I (SYN1), a protein involved in synaptogenesis, synaptic vesicle formation, and regulation of neurotransmitter release. Endogenous Prickle1 and Syn1 co-localize in neurons and physically interact via theSYN1 region mutated in ASD and epilepsy. Finally, a mutation in PRICKLE1 disrupts its ability to increase the size of dense-core vesicles in PC12 cells. Taken together, these findings suggest PRICKLE1 mutations contribute to ASD by disrupting the interaction with SYN1 and regulation of synaptic vesicles.
Joshua Fletcher’s Abstract:
Identification of the candidate virulence gene virK in Francisella tularensis
Francisella tularensis is a highly virulent bacterial pathogen that parasitizes the cytosol of an infected cell. Potentially fatal infections can result from inhalation of as few as 10 organisms, leading the CDC to classify Francisella tularensis as a Tier 1 Select Agent. The bacterium escapes the host cell phagosome by an unknown mechanism dependent on a genomic region known as the Francisella Pathogenicity Island (FPI) and replicates in the nutrient-rich cytosol. Data from a recent transposon mutagenesis screen performed by our lab was combined with protein homology modeling strategies to identify candidate virulence genes in the fully virulent Francisella tularensis Schu S4 strain. One such candidate is encoded by FTT0613c, which we have shown is homologous to virK from various plant pathogens and commensals, as well as the human pathogens Burkholderia and Legionella. A ΔvirK mutant in the Schu S4 strain is attenuated approximately 1,000-fold in murine intranasal infections with an LD50 of 1.15×104 CFU. Vaccination with ΔvirK provided limited protection against 280 CFU of wild type Schu S4 (~30x LD50), increasing time to death by numerous days. Infection of two relevant cell types in vitro (murine bone marrow-derived macrophages and human small airway epithelial cells) indicates that ΔvirK does not proliferate in host cells. Additionally, preliminary data from protein-protein interaction experiments suggest that VirK may interact with host cell proteins. These data support the hypothesis that VirK is a non-FPI virulence factor that may have access to host proteins in the phagosome or cytosol. Furthermore, double and triple mutants in the ΔvirK background may prove useful for the generation of a vaccine strain.