Exploring the potential spinal origins of motor phenotypes in ASD mouse models

Autism Spectrum Disorder (ASD) is a neurodevelopmental disease frequently characterized by movement disorders, including stereotyped repetitive hand movements, difficulties with gait, balance, and coordination, and delays in motor learning. Although all motor behaviors rely on the orderly recruitment of neurons within the brainstem and spinal cord, no studies have investigated the potential contributions of spinal neural circuit defects to ASD motor phenotypes. In this pilot project, the investigators will use cell type-restricted genetic manipulations, transcriptomic, circuit, and behavioral assays in mouse models to explore the role of ASD risk genes in the development and function of spinal motor circuits. They will focus on two genes that cause ASD phenotypes or ASD-related motor symptoms when mutated in humans – Chd8 and Mecp2. Both genes encode nuclear proteins that are essential for the regulation of gene expression in mammals and are abundantly expressed in developing spinal neurons. The researchers will assess the function of Chd8 and Mecp2 in establishing the molecular signatures of spinal neuron classes during mouse embryonic development, postnatal stages, and in the mature nervous system. Examination of changes in gene expression and genomic accessibility in mouse models will be explored, using RNA sequencing (RNAseq) and Assay for Transposase-Accessible Chromatin through sequencing (ATACseq). These assays will explore the hypothesis that mutation in ASD-risk genes leads to changes in spinal neuron gene expression and chromatin structure. In parallel, the researchers will investigate the behavioral consequences and changes in the synaptic inputs to spinal motor neurons after deletion of ASD-associated genes in mice. A battery of motor behavioral tests will be performed on early postnatal (e.g. ambulation, surface righting, negative geotaxis, limb suspension, cliff aversion) and in adult animals (e.g. rotarod, grip strength, beam crossing). Quantitative analyses of limb muscle strength during locomotion will also be examined by electromyography (EMG). Circuit-level changes will be investigated by examining the distribution and number of premotor synaptic inputs onto spinal motor neurons. Collectively, these pilot studies seek to provide foundational data to examine the function of ASD-risk genes in the development and function spinal motor circuits.