Mice lacking Astn2 have ASD-like behaviors and altered cerebellar circuit properties
Astrotactin 2 (ASTN2) is a transmembrane, neuronal protein that functions in receptor trafficking and modulates cerebellar Purkinje cell (PC) synaptic activity. We recently reported a family with a paternally inherited intragenic ASTN2 duplication, with a range of neurodevelopmental disorders, including autism spectrum disorder (ASD), learning difficulties and speech and language delay. To provide a genetic model for the role of the cerebellum in ASD-related behaviors and study ASTN2 role in cerebellar circuit function, we generated global and Purkinje cell-specific conditional Astn2 knockout (KO and cKO, respectively) mouse lines. Astn2 KO mice exhibit strong ASD-related behavioral phenotypes, including a marked decrease in separation-induced pup ultrasonic vocalization (USV) calls, increased hyperactivity and repetitive behaviors, altered social behaviors, and impaired cerebellar-dependent eyeblink conditioning. Increased hyperactivity and repetitive behaviors were also prominent in Astn2 cKO animals. By Golgi staining,  Astn2 KO PCs have region-specific changes in dendritic spine density and filopodia numbers. Proteomic analysis of Astn2 KO cerebellum reveals a marked upregulation of ASTN2 family member, ASTN1, a neuron-glial adhesion protein. Immunohistochemistry and electron microscopy demonstrates a large increase in Bergmann glia volume in the molecular layer of Astn2 KO animals. Electrophysiological experiments indicate a reduced frequency of spontaneous EPSCs, as well as increased amplitudes of both spontaneous EPSCs and IPSCs in the Astn2 KO animals, suggesting that pre- and post-synaptic components of synaptic transmission are altered. Thus, ASTN2 regulates ASD-like behaviors and cerebellar circuit properties. Overall design: We crossed Astn2 WT and KO mice with Tg(Pcp2-L10a-EGFP) bacTRAP line to analyze Purkinje cell-specific gene expression changes in mice lacking ASTN2. Cerebella from WT and KO littermates were isolated at P21 and translating mRNA was isolated using the TRAP methodology.