PROJECT SUMMARY Intellectual disability is a common neurodevelopmental disorder characterized by limited intellectual functioning and impaired adaptive behavior. The clinical heterogeneity of intellectual disability is reflected by extreme genetic complexity, leaving etiology unresolved in over 60% of diagnosed patients. Underscoring this complexity, lesions in more than 700 genes have been linked to intellectual disability. Critically, emerging evidence suggests that this diverse group of these genes converge on a limited set of molecular pathways, principally those critical for brain development and function. This convergence suggests that studies of monogenic, experimentally tractable forms of intellectual disability can provide molecular insight into mechanisms common to all forms of the disease. Interestingly, many of the genes linked to intellectual disability encode RNA binding proteins (RBPs) that play critical roles in post-transcriptional regulation of gene expression. My mentors’ labs co-discovered one such monogenic form of intellectual disability caused by loss of function mutations in the ubiquitously expressed RBP ZC3H14. To discover why mutations in the ZC3H14 gene impair brain function, we have developed an experimentally tractable model of ZC3H14 loss by deleting the ortholog, Nab2, in the fruit fly Drosophila melanogaster. This work has revealed that Nab2 is expressed in all cells but required specifically in neurons within the developing nervous system to support axon guidance, locomotion, and olfactory memory. However, the identity of ZC3H14/Nab2-regulated RNAs as well as mechanisms that elevate ZC3H14/Nab2 function in neurons remain elusive. Recently, my labs have uncovered evidence for a novel role of Nab2 as a regulator of alternative splicing through inhibition of N6-methyladenosine (m6A) deposition on a subset of neuronally enriched mRNAs, representing a critical layer of epitranscriptomic regulation of gene expression during neuronal development. Thus, I will test the hypothesis that Nab2 governs m6A-dependent expression of key neuronal targets by binding their pre-mRNA transcripts and inhibiting m6A hypermethylation to govern proper brain morphology and function here by focusing on one Nab2-regulated transcript, trio, which displays aberrant intron retention upon loss of Nab2. The Trio protein is conserved in vertebrates, the TRIO gene is mutated in a dominant form of human intellectual disability, and Trio plays a key role in axon guidance and neuronal morphology. The Specific Aims of this project are to: 1) define the role of Nab2 as a regulator of m6A-dependent expression of neuronally-enriched transcripts; and 2) examine how Nab2-dependent regulation of Trio expression governs development of axon tracts in the Drosophila mushroom body, an analog of the hippocampus that supports olfactory and gustatory memory. Successful completion of the proposed Aims will provide insights into an apparently conserved pathway linki...