Autism-linked Cullin3 germline haploinsufficiency impacts cytoskeletal dynamics and cortical neurogenesis through RhoA signaling

E3-ubiquitin ligase Cullin3 (Cul3) is a high confidence risk gene for Neurodevelopmental Disorders (NDD) including Autism Spectrum Disorder (ASD) and Developmental Delay (DD). We generated haploinsufficient Cul3 mouse model to investigate brain anatomy, behavior, molecular, cellular, and circuit-level mechanisms dysregulated by Cul3 mutations. Brain MRI of Cul3 mutant animals found profound abnormalities in half of brain regions, including decreased volume of cortical regions and increased volume of subcortical regions. Cul3 mutant mice exhibited social and cognitive deficits, and hyperactive behavior. Spatiotemporal transcriptomic and proteomic profiling of the brain implicated neurogenesis and cytoskeletal defects as key drivers of Cul3 functional impact. Cortical neurons from mutant mice had reduced dendritic length and loss of filamentous actin puncta, along with reduced spontaneous network activity. Inhibition of small GTPase RhoA, a molecular substrate of Cul3 ligase, rescued dendrite length phenotype. This study identified RhoA signaling as a potential mechanism, through which Cul3 mutation impacts early brain development.