Mutations in the X-linked cyclin-dependent kinase-like 5 (CDKL5) gene have been identified in neurodevelopmental disorders including atypical Rett syndrome (RTT), autism spectrum disorders (ASDs), and early infantile epileptic encephalopathy. The biological function of CDKL5 and its role in the etiology of these disorders, however, remain unclear. Here we report the development of a unique knockout mouse model of CDKL5-related disorders and demonstrate that mice lacking CDKL5 show autistic-like deficits in social interaction, as well as impairments in motor control and fear memory. Neurophysiological recordings reveal alterations in event-related potentials (ERPs) similar to those observed in RTT and ASDs. Moreover, kinome profiling uncovers disruption of multiple signal transduction pathways, including the AKTmammalian target of rapamycin (mTOR) cascade, upon Cdkl5 loss-of-function. These data demonstrate that CDKL5 regulates signal transduction pathways and mediates autistic-like phenotypes and together establish a causal role for Cdkl5 loss-of-function in neurodevelopmental disorders.C yclin-dependent kinase-like 5 (CDKL5) is an X-linked gene associated with early infantile epileptic encephalopathy 2 (EIEE2) (1), atypical Rett syndrome (RTT) (2), and autism spectrum disorders (ASDs) (3, 4). Patients with CDKL5 mutations display a heterogenous array of clinical phenotypes, the most prominent of which include early-onset seizures, intellectual disability, and autistic features (5).CDKL5 is a serine/threonine (S/T) kinase that is highly expressed in the brain (6). In vitro studies have demonstrated that CDKL5 may mediate the phosphorylation of methyl-CpG binding protein 2 (MeCP2) (7), DNA methyltransferase 1 (DNMT1) (8), and netrin-G1 ligand (NGL-1) (9). RNAi-mediated knockdown studies show that CDKL5 can regulate neuronal outgrowth and synapse stability (9, 10). Despite these proposed functions, the exact role of CDKL5 in the phosphorylation of MeCP2 (7, 11) and in dendritic outgrowth (9, 10) remains unclear, and thus requires further investigation. The limited understanding of CDKL5 function and its associated signal transduction pathways has hindered the development of therapeutics for CDKL5-related disorders. Current treatments focus on managing symptoms and reducing seizure frequency, but have limited effectiveness (12).To investigate the function of CDKL5 in a disease model and identify potential avenues of therapeutic intervention, we developed a Cdkl5 knockout mouse. We found that mice lacking CDKL5 show autistic-like behavioral abnormalities, deficits in neural circuit communication, and alterations in multiple signal transduction pathways. We establish a causal link between Cdkl5 loss-of-function and disease-related phenotypes and identify the AKT-mammalian target of rapamycin (mTOR) pathway as a unique candidate for targeted therapeutic intervention of CDKL5-related disorders. ResultsGeneration of Cdkl5 Knockout Mice. To investigate the pathophysiology underlying CDKL5-related disorders, we generated ...

Mutations in the MECP2 gene cause the autism spectrum disorder Rett Syndrome (RTT). One of the most common mutations associated with RTT occurs at MeCP2 Threonine 158 converting it to Methionine (T158M) or Alanine (T158A). To understand the role of T158 mutation in the pathogenesis of RTT, we generated knockin mice recapitulating MeCP2 T158A mutation. Here we show a causal role for T158A mutation in the development of RTT-like phenotypes including developmental regression, motor dysfunction, and learning and memory deficits. These phenotypes resemble those in Mecp2-null mice and manifest through a reduction in MeCP2 binding to methylated DNA and a decrease in MeCP2 protein stability. Importantly, the age-dependent development of event-related neuronal responses are disrupted by MeCP2 mutation, suggesting that impaired neuronal circuitry underlies the pathogenesis of RTT and that assessment of event-related potentials may serve as a biomarker for RTT and treatment evaluation.

Mutations in MECP2 cause Rett syndrome (RTT), an X-linked neurological disorder characterized by regressive loss of neurodevelopmental milestones and acquired psychomotor deficits. However, the cellular heterogeneity of the brain impedes an understanding of how MECP2 mutations contribute to RTT. Here we developed a Cre-inducible method for cell type-specific biotin tagging of MeCP2 in mice. Combining this approach with an allelic series of knockin mice carrying frequent RTT mutations (T158M and R106W) enabled the selective profiling of RTT-associated nuclear transcriptomes in excitatory and inhibitory cortical neurons. We found that most gene expression changes are largely specific to each RTT mutation and cell type. Lowly expressed cell type-enriched genes are preferentially disrupted by MeCP2 mutations, with upregulated and downregulated genes reflecting distinct functional categories. Subcellular RNA analysis in MeCP2 mutant neurons further reveals reductions in the nascent transcription of long genes and uncovers widespread post-transcriptional compensation at the cellular level. Finally, we overcame X-linked cellular mosaicism in female RTT models and identified distinct gene expression changes between neighboring wild-type and mutant neurons, altogether providing contextual insights into RTT etiology that support personalized therapeutic interventions.

Dysfunction in sensory information processing is a hallmark of many neurological disorders including autism spectrum disorders (ASDs), schizophrenia and Rett syndrome (RTT)1. Using mouse models of RTT, a monogenic disorder caused by mutations in MECP22, we demonstrate that the large scale loss of MeCP2 from forebrain GABAergic interneurons leads to deficits in auditory event-related potentials (ERPs) and seizure manifestation; but the restoration of MeCP2 in specific classes of interneurons ameliorates these deficits.

Rett syndrome (RTT) is a neurodevelopmental disorder characterized by developmental regression beginning 6–18 months after birth, followed by a lifetime of intellectual disability, stereotyped behaviors, and motor deficits. RTT is caused by mutations in the gene encoding MeCP2, a methyl-CpG binding protein believed to modulate gene transcription. Gene expression studies of individual brain regions have reported that Mecp2 loss-of-function leads to both activation or repression of its gene targets in mice. Conditional deletion of MeCP2 from different brain regions has revealed unique insights into the role of these structures in mediating particular RTT-like phenotypes. However, the function of MeCP2 in the striatum, a major brain region involved in motor control and executive cognitive functions, has yet to be studied. Here, we characterized the gene expression changes in the striatum of Mecp2 mutant mice. We found a number of differentially expressed genes in the striatum of both constitutive Mecp2-null mice and mice lacking MeCP2 only from forebrain GABAergic neurons. These changes only occurred when MeCP2 expression levels had reached mature levels and RTT-like symptoms were manifest, supporting a role for MeCP2 in maintaining proper brain function. Many of the gene expression changes identified in the striatum have not previously been shown to change in the hypothalamus or cerebellum. Bioinformatic analysis of differentially expressed genes in striatum as well as hypothalamus and cerebellum revealed that loss of MeCP2 does not affect the global landscape of gene expression. Additionally, we uncovered a number of differentially expressed genes in the liver of Mecp2-null mice suggesting an important role for MeCP2 in non-neuronal tissues. Collectively, our data suggest that the differential expression of genes following loss of MeCP2 occurs in a tissue, or cell-type specific manner and thus MeCP2 function should be understood in a cellular context.