Fragile X Mental Retardation Protein (FMRP) is an RNA-binding translational regulator implicated in several developmental brain disorders including childhood epilepsy, autism spectrum disorder and Fragile X syndrome. Our lab has established that human FMRP function is completely conserved in the Drosophila disease model, and has repeatedly proven direct relevance to mammalian biology60. The loss of the drosophila FMRP homolog, dFMRP1, is characterized by synaptic overgrowth in both the peripheral and central nervous systems, including the mushroom body (MB) learning and memory center11,13,58. As in humans, Drosophila lacking dFMRP1 exhibit pronounced deficits in learning and memory and are unable to induce activity-dependent pruning of synaptic connectivity12,54. Though these behavioral and cellular phenotypes are well established, the neuronal activity underlying these phenotypes is poorly understood. Using the genetic power of the Drosophila model system I seek to determine the requirements of dFMRP1 in determining and modulating the functional properties of the MB learning and memory center. I hypothesize 1.) FMRP regulates sensory representation and memory consolidation in the MB circuit 2.) FMRP functions in activity- dependent MB circuit function by selectively repressing target mRNA transcripts in response to neuronal activity during the early-use period of Drosophila adult neurodevelopment. 3.) FMRP interacts combinatorially with other mRNA-binding translational regulators, Pumilio and Staufen, to control development stage-specific protein expression driving circuit assembly. I will test these hypotheses using a combination of whole-cell patch clamp recording, Ca2+ imaging, and optogenetic manipulations36-41. I will integrate the IR-DIC optic technology used visualize MB Kenyon cells into our existing electrophysiological recording equipment and follow existing procedures for recording odor evoked activity from both KCs and their innervating projection neurons (PN)36,55,56. I will generate the genetic stocks necessary for calcium imaging and optogenetics experiments as well as the trans-heterozygous mutants for both FMRP and known mRNA binding FMRP interactors stau and pum47,48,64. Together these experiments promise significant contributions to understanding the functional correlates of Fragile X associated learning deficits and sensory hypersensitivity, and offer fundamental insights into the nature of sensory signal transduction, representation, and consolidation.
Fragile X Syndrome is the leading form of inherited intellectual disability and is caused by the loss of a single gene product, the Fragile X Mental Retardation Protein (FMRP). Loss of FMRP is associated with impaired learning and memory, circadian dis-rhythmicity, sensory hypersensitivity, and synaptic overgrowth. This research proposal utilizes the powerful Drosophila genetic system to define the functional requirements of FMRP in the mushroom body learning and memory center.
