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

Abstract

E3-ubiquitin ligase Cullin3 (Cul3) is a high confidence risk gene for autism spectrum disorder (ASD) and developmental delay (DD). To investigate how Cul3 mutations impact brain development, we generated a haploinsufficient Cul3 mouse model using CRISPR/Cas9 genome engineering. Cul3 mutant mice exhibited social and cognitive deficits and hyperactive behavior. Brain MRI found decreased volume of cortical regions and changes in many other brain regions of Cul3 mutant mice starting from early postnatal development. Spatiotemporal transcriptomic and proteomic profiling of embryonic, early postnatal and adult brain implicated neurogenesis and cytoskeletal defects as key drivers of Cul3 functional impact. Specifically, dendritic growth, filamentous actin puncta, and spontaneous network activity were reduced in Cul3 mutant mice. Inhibition of small GTPase RhoA, a molecular substrate of Cul3 ligase, rescued dendrite length and network activity phenotypes. Our study identified defects in neuronal cytoskeleton and Rho signaling as the primary targets of Cul3 mutation during brain development.

Cortical organoids model early brain development disrupted by 16p11.2 copy number variants in autism

“…As we have hypothesized previously, 16p11.2 CNV may impact RhoA signaling through the KCTD13-Cul3 complex, because RhoA is a substrate of the Cul3 ubiquitin ligase, and KCTD13 serves as an adapter protein for Cul3 [45]. Dysregulation of RhoA has previously been observed in KCTD13 [71], TAOK2 [72], and recently in Cul3 [73] mouse models, supporting our hypothesis [45]. Thus, RhoA signaling may be one of the pathways contributing to the neuronal migration defects observed in organoids.…”

insomniac links the development and function of a sleep-regulatory circuit

“…Mosaic analysis of inc is required to discern its developmental functions in postmitotic neurons, to compare its phenotypes with Cul3 , and to distinguish cell autonomous and non-cell autonomous mechanisms. In mammals, Cul3 mutations alter neurogenesis, cortical lamination, neuronal migration, synaptic development, and cause behavioral deficits ( Amar et al, 2021 ; Dong et al, 2020 ; Fischer et al, 2020 ; Rapanelli et al, 2021 ). inc and Cul3 are present at synapses in flies and mammals ( Kikuma et al, 2019 ; Li et al, 2017 ) and are required at the Drosophila larval neuromuscular junction for synaptic homeostasis ( Kikuma et al, 2019 ), a process proposed to be a core function of sleep ( Tononi and Cirelli, 2003 ).…”

Ubiquitin ligases: guardians of mammalian development

“…The final structure of developing organs is determined by cell-to-extracellular matrix and cell-to-cell interactions alongside a series of changes in cellular abundance, shape, and position 133 . E3 ligases can drive these changes by regulating cell-cell fusion (e.g., CUL3-KCTD10 in muscle cell fusion 134 ), extracellular matrix degradation (e.g., RNF31-SHARPIN in mammary glands 135 ), cell migration (e.g., CUL3-BACURD1/2 and cortical neuron migration [136][137][138] ), epithelial-mesenchymal transition (e.g., SMURF2 in mammary glands 139 ), cytoskeletal/structural molecule stability (e.g., CUL3 regulating neuronal cytoskeletal dynamics and Rho signaling 140 and CUL3-Kelch proteins in skeletal muscle 141 ), and cell number (e.g., NEDD4 in the craniofacial complex 142 , CUL4 in the heart 143 , APC/C and MDM2 in the brain and lungs 144,145 )(Figure 2, 4, 5).…”