Mutations in the methyl-CpG binding protein 2 (MECP2) gene cause Rett syndrome (RTT), a neurodevelopmental disorder characterized by the loss of language and motor skills during early childhood. We generated mice with a truncating mutation similar to those found in RTT patients. These mice appeared normal and exhibited normal motor function for about 6 weeks, but then developed a progressive neurological disease that includes many features of RTT: tremors, motor impairments, hypoactivity, increased anxiety-related behavior, seizures, kyphosis, and stereotypic forelimb motions. Additionally, we show that although the truncated MeCP2 protein in these mice localizes normally to heterochromatic domains in vivo, histone H3 is hyperacetylated, providing evidence that the chromatin architecture is abnormal and that gene expression may be misregulated in this model of Rett syndrome.

Genetic deletion of fragile X mental retardation protein (FMRP) has been shown to enhance mGluR-dependent long-term depression (LTD). Herein, we demonstrate that mGluR-LTD induces a transient, translation-dependent increase in FMRP that is rapidly degraded by the ubiquitin-proteasome pathway. Moreover, proteasome inhibitors abolished mGluR-LTD, and LTD was absent in mice that overexpress human FMRP. Neither translation nor proteasome inhibitors blocked the augmentation of mGluR-LTD in FMRP-deficient mice. In addition, mGluR-LTD is associated with rapid increases in the protein levels of FMRP target mRNAs in wild-type mice. Interestingly, the basal levels of these proteins were elevated and their synthesis was improperly regulated during mGluR-LTD in FMRP-deficient mice. Our findings indicate that hippocampal mGluR-LTD requires the rapid synthesis and degradation of FMRP and that mGluR-LTD triggers the synthesis of FMRP binding mRNAs. These findings indicate that the translation, ubiquitination, and proteolysis of FMRP functions as a dynamic regulatory system for controlling synaptic plasticity.

Local translation of proteins in distal dendrites is thought to support synaptic structural plasticity. We have previously shown that metabotropic glutamate receptor (mGluR1) stimulation initiates a phosphorylation cascade, triggering rapid association of some mRNAs with translation machinery near synapses, and leading to protein synthesis. To determine the identity of these mRNAs, a cDNA library produced from distal nerve processes was used to screen synaptic polyribosome-associated mRNA. We identified mRNA for the fragile X mental retardation protein (FMRP) in these processes by use of synaptic subcellular fractions, termed synaptoneurosomes. We found that this mRNA associates with translational complexes in synaptoneurosomes within 1-2 min after mGluR1 stimulation of this preparation, and we observed increased expression of FMRP after mGluR1 stimulation. In addition, we found that FMRP is associated with polyribosomal complexes in these fractions. In vivo, we observed FMRP immunoreactivity in spines, dendrites, and somata of the developing rat brain, but not in nuclei or axons. We suggest that rapid production of FMRP near synapses in response to activation may be important for normal maturation of synaptic connections.Changes in synaptic connectivity are likely to be a key mechanism by which nervous system organization is permanently changed by experience. Local translation of some proteins in dendrites is increasingly considered to be important for changes in synaptic structure and receptor composition. Certain mRNAs are known to be targeted to dendrites (1, 2), and polyribosomal aggregates are observed in or near dendritic spines, more frequently at newly forming synapses (3-5). Dendrites have been shown to be equipped with components necessary for protein synthesis (6), and synthesis of proteins has been demonstrated directly in synaptoneurosomes (7,8) and in preparations of dendrites isolated from hippocampal neurons in culture (9). Local translation of transfected reporter-tagged mRNA has been demonstrated in transected dendrites (10).Protein translation induced by metabotropic receptor stimulation has previously been proposed to play a role in longterm potentiation (LTP), a model for synaptic plasticity (1,11,12). LTP induction also alters levels of specific mRNAs in tissue slices (13), and isotope-tagged leucine is taken up in dendritic regions of hippocampal slices in response to stimulation (14). We have demonstrated that phosphoinositidelinked metabotropic glutamate receptors (mGluR1), known to trigger a phosphorylation cascade, cause certain mRNAs to associate rapidly with protein translation complexes in synaptoneurosomes (15); this process is modulated by ionotropic receptors (16). Furthermore, we have shown that depolarization by 40 mM K ϩ or stimulation by phosphoinositide receptorspecific mGluR agonists increases [ 35 S]methionine incorporation into trichloroacetic acid-precipitable polypeptides (15, 17), indicating that de novo protein synthesis at the synapse occurs as a result of t...

The loss of fragile X mental retardation (FMR1) gene function causes fragile X syndrome (FXS), a common mental retardation syndrome. Anxiety and abnormal social behaviors are prominent features of FXS in humans. To better understand the role of FMR1 in these behaviors, we analyzed anxiety-related and social behaviors in Fmr1 knockout (KO) mice. In the mirrored chamber test, Fmr1 KO mice showed greater aversion to the central mirrored chamber than wild-type (WT) littermates, suggesting increased anxiety-like responses to reflected images of mice. Fmr1 KO mice exhibited abnormal social interactions in a tube test of social dominance, winning fewer matches than WT littermates. In a partition test, Fmr1 KO mice had normal levels of social interest and social recognition. However, during direct interaction tests, Fmr1 KO mice showed significant increases in sniffing behaviors. We further tested the influence of environmental familiarity on the social responses of Fmr1 KO mice to unfamiliar partners. In unfamiliar partitioned cages, Fmr1 KO mice did not differ from WT mice in investigation of unfamiliar partners. However, in familiar partitioned cages, Fmr1 KO mice showed less investigation of a newly introduced partner during the first 5 min and more investigation during the last 5 min of a 20-min partition test, behaviors consistent with initial social anxiety followed by enhanced social investigation. Our findings indicate that the loss of Fmr1 gene function results in altered anxiety and social behavior in mice and demonstrate that the Fmr1 KO mouse is a relevant animal model for the abnormal social responses seen in FXS.

About 35% of patients with 22q11 deletion syndrome (22q11DS), which includes DiGeorge and velocardiofacial syndromes, develops psychiatric disorders, mainly schizophrenia and bipolar disorder. We previously reported that mice carrying a multigene deletion (Df1) that models 22q11DS have reduced prepulse inhibition (PPI), a behavioral abnormality and schizophrenia endophenotype. Impaired PPI is associated with several psychiatric disorders, including those that occur in 22q11DS, and recently, reduced PPI was reported in children with 22q11DS. Here, we have mapped PPI deficits in a panel of mouse mutants that carry deletions that partially overlap with Df1 and have defined a PPI critical region encompassing four genes. We then used single-gene mutants to identify the causative genes. We show that PPI deficits in Df1͞؉ mice are caused by haploinsufficiency of two genes, Tbx1 and Gnb1l. Mutation of either gene is sufficient to cause reduced PPI. Tbx1 is a transcription factor, the mutation of which is sufficient to cause most of the physical features of 22q11DS, but the gene had not been previously associated with the behavioral͞psychiatric phenotype. A likely role for Tbx1 haploinsufficiency in psychiatric disease is further suggested by the identification of a family in which the phenotypic features of 22q11DS, including psychiatric disorders, segregate with an inactivating mutation of TBX1. One family member has Asperger syndrome, an autistic spectrum disorder that is associated with reduced PPI. Thus, Tbx1 and Gnb1l are strong candidates for psychiatric disease in 22q11DS patients and candidate susceptibility genes for psychiatric disease in the wider population.mouse model ͉ psychiatric disease ͉ DiGeorge syndrome ͉ sensorimotor gating C aused by a heterozygous multigene deletion, 22q11 deletion syndrome (22q11DS) is a relatively common genetic disorder (1:4,000 live births). Behavioral and psychiatric disorders are a prominent part of the 22q11DS phenotype. In children, these disorders include cognitive defects, anxiety, attention deficit disorder, and problems of social interaction that are increasingly recognized to meet the criteria of autistic spectrum disorder (1, 2), a neurodevelopmental disorder. In adults, high rates of psychotic disorders, especially schizophrenia, have been reported (2-5).It is likely that the pathophysiological basis of many psychiatric disorders is heterogeneous involving multiple genes and environmental factors. Therefore, when they occur frequently in association with a defined genetic defect, as in the case of 22q11DS (3, 4, 6, 7), it offers a unique opportunity to identify causative or contributing genes, especially if a good animal model is available. We developed a mouse model of 22q11DS (8), the Df1͞ϩ mouse, which carries a heterozygous deletion encompassing 22 genes. Df1͞ϩ mice recapitulate many of the cardiovascular defects associated with 22q11DS (8), and they also display abnormal behavior, including impaired sensorimotor gating, as measured by prepulse inhibition (PPI) o...

Scientific AbstractFragile X syndrome (FXS) is the most common inherited form of intellectual disability in humans. In addition to cognitive impairment, patients may exhibit hyperactivity, attention deficits, social difficulties and anxiety, and autistic-like behaviors. The degree to which patients display these behaviors varies considerably and is influenced by family history, suggesting that genetic modifiers play a role in the expression of behaviors in FXS. Several studies have examined behavior in a mouse model of FXS in which the Fmr1 gene has been ablated. Most of those studies were done in Fmr1 knockout mice on a pure C57BL/6 or FVB strain background. To gain a better understanding of the effects of genetic background on behaviors resulting from the loss of Fmr1 gene expression, we generated F1 hybrid lines from female Fmr1 heterozygous mice on a pure C57BL/6J background bred with male Fmr1 wild-type mice of various background strains (A/J, DBA/2J, FVB/NJ, 129S1/SvImJ and CD-1). Male Fmr1 knockout and wild-type littermates from each line were examined in an extensive behavioral test battery. Results clearly indicate that multiple behavioral responses are dependent on genetic background, including autistic-like traits that are present on limited genetic backgrounds. This approach has allowed us to identify improved models for different behavioral symptoms present in FXS including autistic-like traits. Keywordsfragile X syndrome; autism; genetic; behavior; animal model; mouse model IntroductionFragile X syndrome (FXS) is widely acknowledged as the most common form of inherited intellectual disability (ID). The prevalence of FXS is estimated to be 1/4000 males and 1/8000 females, which accounts for approximately one-third of all X-linked ID cases (Sherman, 2002). The FXS phenotype is often described as clinically indistinct due to the broad spectrum of involvement of the various physical, cognitive, and behavioral abnormalities associated with the syndrome. What is often less appreciated, but which may be more critical to the overall quality of life, is the fact that individuals with FXS have several other behavioral abnormalities including: attention deficit, hyperactivity/ hyperkinesis, anxiety, depression, irritability, mania, obsessive-compulsive behavior, aggression, and self-injurious behavior (Hagerman, 2002). FXS patients are also hypersensitive to many different sensory stimuli. Interestingly, a number of autistic-like * Correspondence: Richard Paylor, rpaylor@bcm.edu, NIH Public Access NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript behaviors have been associated with FXS, including poor eye contact, tactile defensiveness, hand biting, hand flapping, and perseveration of speech and behavior (Hagerman, 2002). An estimated 21-50% of individuals with FXS meet diagnostic criteria for autistic disorder, displaying social difficulty, communication problems and perseverative or repetitive behaviors (Moss & Howlin, 2009). Like many complex genetic syndromes, there is significant...

Angelman syndrome (AS) is a neurobehavioral disorder associated with mental retardation, absence of language development, characteristic electroencephalography (EEG) abnormalities and epilepsy, happy disposition, movement or balance disorders, and autistic behaviors. The molecular defects underlying AS are heterogeneous, including large maternal deletions of chromosome 15q11–q13 (70%), paternal uniparental disomy (UPD) of chromosome 15 (5%), imprinting mutations (rare), and mutations in the E6-AP ubiquitin ligase gene UBE3A (15%). Although patients with UBE3A mutations have a wide spectrum of neurological phenotypes, their features are usually milder than AS patients with deletions of 15q11–q13. Using a chromosomal engineering strategy, we generated mutant mice with a 1.6-Mb chromosomal deletion from Ube3a to Gabrb3, which inactivated the Ube3a and Gabrb3 genes and deleted the Atp10a gene. Homozygous deletion mutant mice died in the perinatal period due to a cleft palate resulting from the null mutation in Gabrb3 gene. Mice with a maternal deletion (m−/p+) were viable and did not have any obvious developmental defects. Expression analysis of the maternal and paternal deletion mice confirmed that the Ube3a gene is maternally expressed in brain, and showed that the Atp10a and Gabrb3 genes are biallelically expressed in all brain sub-regions studied. Maternal (m−/p+), but not paternal (m+/p−), deletion mice had increased spontaneous seizure activity and abnormal EEG. Extensive behavioral analyses revealed significant impairment in motor function, learning and memory tasks, and anxiety-related measures assayed in the light-dark box in maternal deletion but not paternal deletion mice. Ultrasonic vocalization (USV) recording in newborns revealed that maternal deletion pups emitted significantly more USVs than wild-type littermates. The increased USV in maternal deletion mice suggests abnormal signaling behavior between mothers and pups that may reflect abnormal communication behaviors in human AS patients. Thus, mutant mice with a maternal deletion from Ube3a to Gabrb3 provide an AS mouse model that is molecularly more similar to the contiguous gene deletion form of AS in humans than mice with Ube3a mutation alone. These mice will be valuable for future comparative studies to mice with maternal deficiency of Ube3a alone.

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