Role of FMRP interactions with presynaptic ion channels in Fragile X Syndrome
Chhavi graduated with her B.Sc. in Microbiology from University of Pune, India, followed by a M.S. in Biology from University of Massachusetts, Lowell and a Ph.D. from University of Virginia. During her Ph.D. in the lab of Sarah Siegrist, her research was focused on how Notch signaling controls both the termination of neurogenesis and the ability of neural stem cells to enter quiescent stages during developmental transitions. For her postdoctoral research, Chhavi is interested in studying neurological disease models. Her proposed project will use the Drosophila Fragile X model to examine non-canonical roles for FMRP in presynaptic channel trafficking and synapse accumulation.
Fragile X Syndrome (FXS), a leading genetic cause of autism, causes defective synaptic communication due to silencing of the FMR1 gene by repeat expansion. Two major functions for the FMRP protein include mRNA binding to regulate protein translation and direct interactions with presynaptic Cav2 (voltage-gated Ca2+ channels) and BK (Ca2+-activated K+ channels) channels independent of RNA binding. This later function is proposed to control surface levels of Cav2 and BK, though it is unclear how FMRP binding modulates their abundance at active zones (AZs), where synaptic vesicles release. Although biosynthesis, delivery and recycling cooperate to establish AZ protein abundance, experimentally isolating these distinct regulatory processes is difficult. The Littleton lab has generated new genetic toolkits to determine how the AZ levels of Cacophony (Cac). I will generate similar toolkits for the sole Drosophila BK channel (Slo). Using intravital FRAP and mMaple photoconversion, I propose to measure delivery and turnover of these proteins at individual AZs over a course of time in controls and mutants of the Drosophila FMRP homolog, dFXR. I will combine this analysis with electrophysiology, optical quantal analysis and presynaptic Ca2+ imaging to determine how loss of FMRP alters synaptic communication, and if these defects are secondary to abnormal Cac and Slo abundance or function at AZs. Together, these experiments will reveal how FMRP controls Cac and Slo synaptic delivery and AZ abundance, and how dysregulation of these interactions contributes to synaptic defects in FXS.
Neuronal communication, FMRP, electrophysiology, Calcium imaging