Global mapping of altered neural circuits in a mouse model of DDX3X mutations

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PROJECT SUMMARY Autism spectrum disorder (ASD) is a prevalent neurodevelopmental disorder with dozens of highly penetrant risk alleles and yet no effective pharmacological treatment. Mutations in the X-linked gene DDX3X are a high-risk factor for ASD. Affected individuals are predominantly females, so studying DDX3X might offer insights into sex differences in brain development and function. DDX3X encodes a DEAD-box RNA helicase critical for mRNA metabolism. DDX3X is broadly expressed, and its functions in the brain are just beginning to emerge: Ddx3x regulates cortical neurogenesis, hindbrain development, and synaptogenesis. However, we do not know the circuit-level determinants of DDX3X mutations. There is a critical need to fill these gaps because, until we do so, deciphering the complexity of ASD and developing effective therapeutics remain out of reach. To address this unmet need, a mouse with construct and face validity for DDX3X mutations was generated in our laboratory (Ddx3x+/- mice). The long-term goal is to understand the cellular and circuitry biology of ASD and identify new targets for therapeutic intervention. The overall objective is to capture the neural mechanisms of mutations in the ASD risk gene DDX3X with multimodal and holistic profiling. The central hypothesis is that Ddx3x regulates the molecular identity, connectivity, and activity of corticofugal circuits subserving complex behaviors. The rationale is that, once we identify reliable neural substrates, mechanism-based therapeutics can be developed and tested pre-clinically. The hypothesis will be tested by pursuing three Specific Aims: 1) Identify the cortical populations and the molecular signatures affected in Ddx3x+/- mice; 2) Map brain-wide neural ensembles with altered connectivity and/or activity in Ddx3x+/- mice; and, 3) Dissect and manipulate corticofugal circuits driving abnormal behavior in Ddx3x+/- mice. Under Aim 1, the major molecular and cellular ensembles affected by Ddx3x mutations will be identified using single-cell transcriptomics and 3D cellular mapping. Under Aim 2, activity-based neural substrates that are disrupted by Ddx3x mutations will be dissected using 3D mapping of immediate-early genes expression after behavior. Under Aim 3, circuits will be manipulated with chemogenetics approaches. The proposal is innovative because it uses cutting-edge methods to map the 3D landscape of defined neuronal populations and whole-brain activity through the entire brain of a novel ASD mouse model. It is also innovative because DDX3X is a high-confidence risk gene for ASD just recently discovered, and its role on shaping brain circuits is still completely unknown. The application is significant because it will advance our understanding of ASD complexity by reaching whole-brain, circuitry-level resolution, while propelling the development of a robust platform to probe convergences across models and developmental stages. These results are expected to have a positive impact because they will pave the way for novel therapeutic interventions for ASD.