IMPACT OF LOSS OF THE AUTISM RISK GENE CHD8 ON EXPRESSION, EPIGENETICS AND CELLULAR FUNCTIONING OF THE DOPAMINERGIC SYSTEM

PROJECT SUMMARY Dr. Rebecca Muhle is a practicing child psychiatrist and an Early Stage Investigator with a strong track record of developing molecular genetic tools to elucidate the mechanism of neurodevelopmental disorders. Her long- term goal is to identify cell types, circuits and regulatory networks affected by loss of Chromodomain Helicase DNA-binding Protein 8 (CHD8), a high confidence autism spectrum disorder (ASD) risk gene. Dr. Muhle initiated her studies of CHD8 during her fellowship with James Noonan, Ph.D. with co-mentorship by Matthew State, M.D., Ph.D. She successfully obtained research funding from the National Institute for Mental Health and the Simons Foundation for Autism Research to determine the impact of CHD8 and its loss on regulatory networks of the developing cortex, and she showed that CHD8 in developing cortex regulates other ASD risk genes. She is extending this research at Columbia University in collaboration with Jeremy Veenstra-VanderWeele, M.D. and Muhammed Osman Chohan, M.D., experts in translational animal models of neurobehavioral disorders and the study of monoaminergic neurotransmission. Together, they have found reduced stereotypy and attenuated hyperlocomotor activity in male, but not female Chd8+/- mice after inhibition of the dopamine transporter, with an intact response to dopamine receptor agonism, suggesting that CHD8 plays a critical role in the development of the dopaminergic circuit between the midbrain and striatum. The overall objective of this R01 proposal is to elucidate the mechanisms whereby CHD8 genetic mutations affect cells and pathways critical for core symptoms of ASD and other neurodevelopmental disorders, by integrating state-of-the-art single nuclear transcriptomics and cell type specific functional genomics with electrophysiologic and behavioral probing of animal models with a loss of CHD8 expression. The following three independent specific aims will address the central hypothesis that CHD8 regulates genes that are critical for the function of the basal ganglia and dopaminergic system, and that loss of CHD8 will dysregulate these genes and other ASD risk genes. This project will 1) identify the cellular, transcriptional, and epigenetic changes in the developing Chd8+/- mouse ventral midbrain and striatum using single nuclear RNA sequencing (snRNAseq) and chromatin accessibility (snATACseq), 2) elucidate how CHD8 loss causes a defect in the molecular transmission of the DA stimulus in the basal ganglia using fiber photometry and in vivo extracellular recordings using constitutive and conditional CHD8 haploinsufficiency mouse models, and 3) localize CHD8 binding activity in specific cell types of the dopaminergic system using chromatin immunoprecipitation and sequencing of a conditionally biotinylated Chd8-tag transgene. By studying CHD8, a key regulatory molecule that targets other ASD risk genes, Dr. Muhle will close a critical knowledge gap in the role of CHD8 in the circuitry implicated in ASD-related behaviors.