The proposed research addresses a critically important question in autism spectrum disorder (ASD) research: how defects in cerebellar circuits contribute to ASD. In particular, it examines the role of the predominantly cerebellar gene ASTN2 in cerebellar circuit function and ASD-related behaviors. Copy number variations (CNVs) in ASTN2 have been identified as a significant risk factor for ASD (Lionel et al, 2014), suggesting that ASTN2 mutations such as those found in patients with ASTN2 CNVs, lead to altered cerebellar synaptic function. In addition, we recently reported a family with a paternally inherited intragenic ASTN2 duplication, which caused a heterozygous loss of function of ASTN2. The family manifested a range of neurodevelopmental disorders, including ASD, learning difficulties and speech and language delay (Behesti et al, 2018). Our cellular and molecular studies on mouse cerebellum show that ASTN2 binds to and regulates the trafficking of multiple synaptic proteins, including Neuroligins, which have been genetically linked to ASDs, and modulates cerebellar Purkinje cell (PC) synaptic activity (Behesti et al, 2018). To provide a genetic model to study cerebellar circuit function, we generated both a global loss of function Astn2 line and a floxed Astn2 line for conditional knockout experiments. New, preliminary evidence indicates that PCs in mice lacking Astn2 have a decrease in evoked excitation relative to inhibition in PCs and reduced PC dendritic spine density, suggesting specific cerebellar circuit defects. In addition, preliminary evidence shows mild motor deficits and defects in USVs and an open field assay, ASD-related behaviors. As other preliminary findings do not indicate major defects in cerebellar development, we hypothesize that the behavioral defects we observed relate to defects in the cerebellar circuitry with underlying changes in receptor trafficking. In the proposed research, we will 1) test how loss of Astn2 alters intrinsic excitability in PCs and the synaptic efficacy of their presynaptic inputs from GCs and molecular layer interneurons, 2) use proteomics to identify changes in the levels of synaptic proteins and live imaging to assess whether such changes relate to changes in the rate of endocytosis, 3) compare changes in PC dendritic branching as well as the regional distribution of PC spines in wild type and mutant animals to provide insight on whether there are changes in the organization of PC inputs during the establishment of the cerebellar circuitry, and 4) analyze changes in social behavior and ultrasonic vocalization in Astn2 wild type, heterozygous and mutant animals. Taken together, the proposed research will provide a new mouse model that allows us to link an ASD-related gene that is predominantly expressed in the cerebellum with specific cerebellar circuit function and molecular pathways.
The proposed research addresses a critically important question in autism spectrum disorder (ASD) research: how defects in cerebellar circuits contribute to ASD. Neurogenetic studies demonstrate that CNVs in the predominantly cerebellar gene ASTN2 are a significant risk factor for ASD. The proposed research will use a novel mouse model lacking Astn2 that we generated to analyze changes in cerebellar circuit function, synaptic proteins, organization of synaptic inputs and ASD-related changes in social behavior and communication.
