Atypical brain connectivity is a major contributor to the pathophysiology of neurodevelopmental disorders (NDDs) including autism spectrum disorders (ASDs). TAOK2 is one of several genes in the 16p11.2 microdeletion region, but whether it contributes to NDDs is unknown. We performed behavioral analysis on Taok2 heterozygous (Het) and knockout (KO) mice and found gene dosage-dependent impairments in cognition, anxiety, and social interaction. Taok2 Het and KO mice also have dosage-dependent abnormalities in brain size and neural connectivity in multiple regions, deficits in cortical layering, dendrite and synapse formation, and reduced excitatory neurotransmission. Whole-genome and -exome sequencing of ASD families identified three de novo mutations in TAOK2 and functional analysis in mice and human cells revealed that all the mutations impair protein stability, but they differentially impact kinase activity, dendrite growth, and spine/synapse development. Mechanistically, loss of Taok2 activity causes a reduction in RhoA activation, and pharmacological enhancement of RhoA activity rescues synaptic phenotypes. Together, these data provide evidence that TAOK2 is a neurodevelopmental disorder risk gene and identify RhoA signaling as a mediator of TAOK2-dependent synaptic development.

Adult zebrafish, in contrast to mammals, regrow axons descending from the brainstem after spinal cord transection. L1.1, a homolog of the mammalian recognition molecule L1, is upregulated by brainstem neurons during axon regrowth. However, its functional relevance for regeneration is unclear. Here, we show with a novel morpholino-based approach that reducing L1.1 protein expression leads to impaired locomotor recovery as well as reduced regrowth and synapse formation of axons of supraspinal origin after spinal cord transection. This indicates that L1.1 contributes to successful regrowth of axons from the brainstem and locomotor recovery after spinal cord transection in adult zebrafish.

Traumatic events can engender persistent excessive fear responses to trauma reminders that may return even after successful treatment. Extinction, the laboratory analog of behavior therapy, does not erase conditioned fear memories but generates competing, fearinhibitory "extinction memories" that, however, are tied to the context in which extinction occurred. Accordingly, a dominance of fear over extinction memory expression-and, thus, return of fear-is often observed if extinguished fear stimuli are encountered outside the extinction (therapy) context. We show that postextinction administration of the dopamine precursor L-dopa makes extinction memories context-independent, thus strongly reducing the return of fear in both mice and humans. Reduced fear is accompanied by decreased amygdala and enhanced ventromedial prefrontal cortex activation in both species. In humans, ventromedial prefrontal cortex activity is predicted by enhanced resting-state functional coupling of the area with the dopaminergic midbrain during the postextinction consolidation phase. Our data suggest that dopamine-dependent boosting of extinction memory consolidation is a promising avenue to improving anxiety therapy.fear conditioning | psychotherapy | reinstatement | renewal | resilience

The extracellular matrix glycoprotein tenascin-C (TN-C) has been suggested to play important functional roles during neural development, axonal regeneration, and synaptic plasticity. We generated a constitutively TN-C-deficient mouse mutant from embryonic stem cells with a floxed tn-C allele, representing a standard for future analysis of conditionally targeted mice. The gross morphology of the CNS was not detectably affected, including no evidence for perturbed nerve cell migration, abnormal oligodendrocyte distribution, or defective myelination. Despite the apparent normal histology of the hippocampus and normal performance in the water maze, theta-burst stimulation (TBS) of Schaffer collaterals elicited reduced long-term potentiation (LTP) in the CA1 region of TN-C-deficient mutants, as compared with wild-type littermates. However, high-frequency stimulation evoked normal LTP not only in CA1, but also at mossy fiber-CA3 and medial and lateral perforant path-granule cell synapses in the dentate gyrus. Low-frequency stimulation failed to induce long-term depression in the CA1 region of TN-C-deficient animals. Recordings of TBS-induced LTP in the presence of nifedipine, an antagonist of L-type voltage-dependent Ca2+ channels (VDCCs), did not affect LTP in TN-C-deficient mice, but reduced LTP in wild-type mice to the levels seen in mutants. Furthermore, chemical induction of a L-type VDCC-dependent LTP in the CA1 region by application of the K+ channel blocker tetraethylammonium resulted in impaired LTP in TN-C mutants. Thus, reduction in L-type VDCC-mediated signaling appears to mediate the deficits in certain forms of synaptic plasticity in constitutively TN-C-deficient mice.

The nervous system is vulnerable to perturbations during specific developmental periods. Insults during such susceptible time windows can have long-term consequences, including the development of neurological diseases such as epilepsy. Here we report that a pharmacological intervention timed during a vulnerable neonatal period of cortical development prevents pathology in a genetic epilepsy model. By using mice with dysfunctional Kv7 voltage-gated K(+) channels, which are mutated in human neonatal epilepsy syndromes, we demonstrate the safety and efficacy of the sodium-potassium-chloride cotransporter NKCC1 antagonist bumetanide, which was administered during the first two postnatal weeks. In Kv7 current-deficient mice, which normally display epilepsy, hyperactivity and stereotypies as adults, transient bumetanide treatment normalized neonatal in vivo cortical network and hippocampal neuronal activity, prevented structural damage in the hippocampus and restored wild-type adult behavioral phenotypes. Furthermore, bumetanide treatment did not adversely affect control mice. These results suggest that in individuals with disease susceptibility, timing prophylactically safe interventions to specific windows during development may prevent or arrest disease progression.

Phosphorylated creatine (Cr) serves as an energy buffer for ATP replenishment in organs with highly fluctuating energy demand. The central role of Cr in the brain and muscle is emphasized by severe neurometabolic disorders caused by Cr deficiency. Common symptoms of inborn errors of creatine synthesis or distribution include mental retardation and muscular weakness. Human mutations in l-arginine:glycine amidinotransferase (AGAT), the first enzyme of Cr synthesis, lead to severely reduced Cr and guanidinoacetate (GuA) levels. Here, we report the generation and metabolic characterization of AGAT-deficient mice that are devoid of Cr and its precursor GuA. AGAT-deficient mice exhibited decreased fat deposition, attenuated gluconeogenesis, reduced cholesterol levels and enhanced glucose tolerance. Furthermore, Cr deficiency completely protected from the development of metabolic syndrome caused by diet-induced obesity. Biochemical analyses revealed the chronic Cr-dependent activation of AMP-activated protein kinase (AMPK), which stimulates catabolic pathways in metabolically relevant tissues such as the brain, skeletal muscle, adipose tissue and liver, suggesting a mechanism underlying the metabolic phenotype. In summary, our results show marked metabolic effects of Cr deficiency via the chronic activation of AMPK in a first animal model of AGAT deficiency. In addition to insights into metabolic changes in Cr deficiency syndromes, our genetic model reveals a novel mechanism as a potential treatment option for obesity and type 2 diabetes mellitus.

The balance between excitation and inhibition controls fundamental aspects of the hippocampal function. Here, we report an increase in the ratio of inhibitory to excitatory neurons in the dentate gyrus, accompanied by γ-aminobutyric acid(A) (GABA(A)) receptor-dependent impairment of synaptic plasticity and enhancement of activity-dependent changes in excitability in anesthetized adult mice deficient for the extracellular matrix glycoprotein tenascin-R (TNR). TNR-deficient mice showed faster reversal learning, improved working memory, and enhanced reactivity to novelty than wild-type littermates. Remarkably, in wild-type and TNR-deficient mice, faster reversal learning rates correlated at the individual animal level with ratios of parvalbumin-positive interneurons to granule cells and densities of parvalbumin-positive terminals on somata of granule cells. Our data demonstrate that modification of the extracellular matrix by ablation of TNR leads to a new structural and functional design of the dentate gyrus, with enhanced GABAergic innervation, that is, enhanced ratio of inhibitory to excitatory cells, and altered plasticity, promoting working memory and reversal learning. In wild-type mice, the enhanced ratio of inhibitory to excitatory cells in the dentate gyrus also positively correlated with reversal learning, indicating that level of inhibition regulates specific aspects of learning independent of the TNR gene.

IRSp53 is an essential intermediate between the activation of Rac and Cdc42GTPases and the formation of cellular protrusions; it affects cell shape by coupling membrane-deforming activity with the actin cytoskeleton. IRSp53 is highly expressed in neurons where it is also an abundant component of the postsynaptic density (PSD). Here we analyze the physiological function of this protein in the mouse brain by generating IRSp53-deficient mice. Neurons in the hippocampus of young and adult knock-out (KO) mice do not exhibit morphological abnormalities in vivo. Conversely, primary cultured neurons derived from IRSp53 KO mice display retarded dendritic development in vitro. On a molecular level, Eps8 cooperates with IRSp53 to enhance actin bundling and interacts with IRSp53 in developing neurons. However, postsynaptic Shank proteins which are expressed at high levels in mature neurons compete with Eps8 to block actin bundling. In electrophysiological experiments the removal of IRSp53 increases synaptic plasticity as measured by augmented long term potentiation and pairedpulse facilitation. A primarily postsynaptic role of IRSp53 is underscored by the decreased size of the PSDs, which display increased levels of N-methyl-D-aspartate receptor subunits in IRSp53 KO animals. Our data suggest that the incorporation of IRSp53 into the PSD enables the protein to limit the number of postsynaptic glutamate receptors and thereby affect synaptic plasticity rather than dendritic morphology. Consistent with altered synaptic plasticity, IRSp53-deficient mice exhibit cognitive deficits in the contextual fear-conditioning paradigm.Rho GTPases such as Cdc42, Rac, and Rho control key events in neuronal cell biology, including the generation of neuronal polarity and morphology, establishment of dendritic spines, the generation of postsynaptic specializations and synaptic plasticity (1, 2). Specificity in these processes is thought to arise through control of different downstream targets which are recognized and activated by the active, GTP-bound forms of Rho family members. The insulin receptor substrate of 53 kDa (IRSp53) 3 is an essential mediator between activated Rac or Cdc42 and the formation of lamellipodia or filopodia, respectively. GTPase binding to IRSp53 enables interactions of its SH3 domain with downstream effectors WAVE2, Mena, Eps8, or N-WASP, all of which are known regulators of actin dynamics (3-6). In addition, the N-terminal IRSp53/missing in metastasis homology domain of IRSp53 assists in generating cellular protrusions by bundling actin filaments (5, 7, 8) and promoting membrane curvature (9, 10). Expression of IRSp53 is particularly high in the brain, and consequently IRSp53 contributes to the formation of dendritic spines in the cultured hippocampal neuron model (11).Via the SH3 domain and a C-terminal PDZ binding motif, IRSp53 also bridges postsynaptic shank and PSD-95 family members (11)(12)(13)(14). A significant enrichment in the postsynaptic density (PSD) of excitatory synapses suggests that Rac/Cdc42 signalin...