ABSTRACT Fragile X Mental Retardation Protein (FMRP) is an RNA binding protein that binds to specific mRNAs to control their location and protein translation, thus regulating the expression of important genes in neuronal development, neuronal function and synaptic plasticity. FMRP’s critical role is demonstrated by the neurodevelopmental disorder, Fragile X syndrome (FXS) that is caused by a lack of FMRP due to mutations in the FMR1 gene. Although the function of FMRP has been extensively explored in animal models, how FMRP functions in human neuronal development and how a lack of FMRP causes the devastating characteristics in FXS patients are largely unknown. The experiments in this discovery-based proposal seek to identify mRNA targets of FMRP in human neurons for the first time. Human pluripotent stem cells with the endogenous FMR1 gene FLAG tagged will be differentiated into forebrain excitatory and inhibitory neurons. FMRP targets will be identified by crosslinking immunoprecipitation (CLIP) with an antibody against the FLAG tag, followed by deep sequencing (RNA-seq). We will then investigate whether FMRP targets identified in mouse neurons are also regulated by FMRP in human neurons as well as validate the FMRP bound mRNAs identified in Aim 1 and perform initial functional analyses of these mRNAs. The data will unveil potential mechanisms for FMRP’s role in human neuronal development. The data will enable better understanding of how lack of FMRP in FXS causes intellectual disability and potentially autism.

PROJECT NARRATIVE Fragile X syndrome (FXS) is the most common heritable cause of intellectual disability and autism and is caused by a lack of Fragile X Mental Retardation Protein (FMRP). FMRP binds to specific messenger RNAs (mRNAs) in the brain to control their stability, localization, and expression. This proposal seeks to identify the mRNA targets of FMRP in human neurons. Despite the important function of FMRP and the fact that FXS may serve as a gateway for understanding autism, the function of FMRP in human neuronal development and function is not well understood.