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An autism‐associated gene Shank3 encodes multiple splicing isoforms, Shank3a‐f. We have recently reported that Shank3a/b‐knockout mice were more susceptible to kainic acid‐induced seizures than wild‐type mice at 4 weeks of age. Little is known, however, about how the N‐terminal and ankyrin repeat domains (NT‐Ank) of Shank3a/b regulate multiple molecular signals in the developing brain. To explore the functional roles of Shank3a/b, we performed a mass spectrometry‐based proteomic search for proteins interacting with GFP‐tagged NT‐Ank. In this study, NT‐Ank was predicted to form a variety of complexes with a total of 348 proteins, in which RNA‐binding (n = 102), spliceosome (n = 22), and ribosome‐associated molecules (n = 9) were significantly enriched. Among them, an X‐linked intellectual disability‐associated protein, Nono, was identified as a NT‐Ank‐binding protein. Coimmunoprecipitation assays validated the interaction of Shank3 with Nono in the mouse brain. In agreement with these data, the thalamus of Shank3a/b‐knockout mice aberrantly expressed splicing isoforms of autism‐associated genes, Nrxn1 and Eif4G1, before and after seizures with kainic acid treatment. These data indicate that Shank3 interacts with multiple RNA‐binding proteins in the postnatal brain, thereby regulating the homeostatic expression of splicing isoforms for autism‐associated genes after birth. [ABSTRACT FROM AUTHOR]

Proper neurological function in humans requires precise control of levels of the epigenetic regulator methyl CpG-binding protein 2 (MeCP2). MeCP2 protein levels are low in fetal brains, where the predominant MECP2 transcripts have an unusually long 3' untranslated region (UTR). Here, we show that miR-483-5p, an intragenic microRNA of the imprinted IGF2, regulates MeCP2 levels through a human-specific binding site in the MECP2 long 3' UTR. We demonstrate the inverse correlation of miR-483-5p and MeCP2 levels in developing human brains and fibroblasts from Beckwith-Wiedemann syndrome patients. Importantly, expression of miR-483-5p rescues abnormal dendritic spine phenotype of neurons overexpressing human MeCP2. In addition, miR-483-5p modulates the levels of proteins of the MeCP2-interacting corepressor complexes, including HDAC4 and TBL1X. These data provide insight into the role of miR-483-5p in regulating the levels of MeCP2 and interacting proteins during human fetal development.

The cytoplasmic FMR1-interacting protein 2 (CYFIP2) have diverse molecular functions in neurons, including the regulation of actin polymerization, mRNA translation, and mitochondrial morphology and function. Mutations in the CYFIP2 gene are associated with early-onset epilepsy and neurodevelopmental disorders, while decreases in its protein levels are linked to Alzheimer's disease (AD). Notably, previous research has revealed AD-like phenotypes, such as dendritic spine loss, in the hippocampal CA1 pyramidal neurons of 12-month-old Cyfip2 heterozygous mice but not of age-matched CA1 pyramidal neuron-specific Cyfip2 conditional knock-out (cKO) mice. This study aims to investigate whether dendritic spine loss in Cyfip2 cKO mice is merely delayed compared to Cyfip2 heterozygous mice, and to explore further neuronal phenotypes regulated by CYFIP2 in aged mice. We characterized dendrite and dendritic protrusion morphologies, along with excitatory/inhibitory synapse densities in CA1 pyramidal neurons of 17-month-old Cyfip2 cKO mice. Overall dendritic branching was normal, with a reduction in the length of basal, not apical, dendrites in CA1 pyramidal neurons of Cyfip2 cKO mice. Furthermore, while dendritic protrusion density remained normal, alterations were observed in the length of mushroom spines and the head volume of stubby spines in basal, not apical, dendrites of Cyfip2 cKO mice. Although excitatory synapse density remained unchanged, inhibitory synapse density increased in apical, not basal, dendrites of Cyfip2 cKO mice. Consequently, a cell-autonomous reduction of CYFIP2 appears insufficient to induce dendritic spine loss in CA1 pyramidal neurons of aged mice. However, CYFIP2 is required to maintain normal dendritic length, dendritic protrusion morphology, and inhibitory synapse density. [ABSTRACT FROM AUTHOR]

Here, we report the generation and comprehensive characterization of a knockin mouse model for the hotspot p.Arg87Cys variant of the cytoplasmic FMR1‐interacting protein 2 (CYFIP2) gene, which was recently identified in individuals diagnosed with West syndrome, a developmental and epileptic encephalopathy. The Cyfip2+/R87C mice recapitulated many neurological and neurobehavioral phenotypes of the patients, including spasmlike movements, microcephaly, and impaired social communication. Age‐progressive cytoarchitectural disorganization and gliosis were also identified in the hippocampus of Cyfip2+/R87C mice. Beyond identifying a decrease in CYFIP2 protein levels in the Cyfip2+/R87C brains, we demonstrated that the p.Arg87Cys variant enhances ubiquitination and proteasomal degradation of CYFIP2. ANN NEUROL 2023;93:155–163 [ABSTRACT FROM AUTHOR]

An increasing number of neuropsychiatric disorders such as autism spectrum disorder (ASD), intellectual disability, schizophrenia, obsessive-compulsive disorder and bipolar disorder are being classified as 'synaptopathies' (1-4), because the genes mutated [...], Mutations in SHANK3 and large duplications of the region spanning SHANK3 both cause a spectrum of neuropsychiatric disorders, indicating that proper SHANK3 dosage is critical for normal brain function. However, SHANK3 overexpression per se has not been established as a cause of human disorders because 22q13 duplications involve several genes. Here we report that Shank3 transgenic mice modelling a human SHANK3 duplication exhibit manic-like behaviour and seizures consistent with synaptic excitatory/inhibitory imbalance. We also identified two patients with hyperkinetic disorders carrying the smallest SHANK3-spanning duplications reported so far. These findings indicate that SHANK3 overexpression causes a hyperkinetic neuropsychiatric disorder. To probe the mechanism underlying the phenotype, we generated a Shank3 in vivo interactome and found that Shank3 directly interacts with the Arp2/3 complex to increase F-actin levels in Shank3 transgenic mice. The mood-stabilizing drug valproate, but not lithium, rescues the manic-like behaviour of Shank3 transgenic mice raising the possibility that this hyperkinetic disorder has a unique pharmacogenetic profile.