Towards Preclinical Validation of Arbaclofen (R-baclofen) Treatment for 16p11.2 Deletion Syndrome.

A microdeletion on human chromosome 16p11.2 is one of the most common copy number variants associated with autism spectrum disorder and other neurodevelopmental disabilities. Arbaclofen, a GABA(B) receptor agonist, is a component of racemic baclofen, which is FDA-approved for treating spasticity, and has been shown to alleviate behavioral phenotypes, including recognition memory deficits, in animal models of 16p11.2 deletion. Given the lack of reproducibility sometimes observed in mouse behavioral studies, we brought together a consortium of four laboratories to study the effects of arbaclofen on behavior in three different mouse lines with deletions in the mouse region syntenic to human 16p11.2 to test the robustness of these findings. Arbaclofen rescued cognitive deficits seen in two 16p11.2 deletion mouse lines in traditional recognition memory paradigms. Using an unsupervised machine-learning approach to analyze behavior, one lab found that arbaclofen also rescued differences in exploratory behavior in the open field in 16p11.2 deletion mice. Arbaclofen was not sedating and had modest off-target behavioral effects at the doses tested. Our studies show that arbaclofen consistently rescues behavioral phenotypes in 16p11.2 deletion mice, providing support for clinical trials of arbaclofen in humans with this deletion.

Twenty years of discoveries emerging from mouse models of autism.

More than 100 single gene mutations and copy number variants convey risk for autism spectrum disorder. To understand the extent to which each mutation contributes to the trajectory of individual symptoms of autism, molecular genetics laboratories have introduced analogous mutations into the genomes of laboratory mice and other species. Over the past twenty years, behavioral neuroscientists discovered the consequences of mutations in many risk genes for autism in animal models, using assays with face validity to the diagnostic and associated behavioral symptoms of people with autism. Identified behavioral phenotypes complement electrophysiological, neuroanatomical, and biochemical outcome measures in mutant mouse models of autism. This review describes the history of phenotyping assays in genetic mouse models, to evaluate social and repetitive behaviors relevant to the primary diagnostic criteria for autism. Robust phenotypes are currently employed in translational investigations to discover effective therapeutic interventions, representing the future direction of an intensely challenging research field.

Sexually dimorphic neuroanatomical differences relate to ASD-relevant behavioral outcomes in a maternal autoantibody mouse model.

Immunoglobulin G (IgG) autoantibodies reactive to fetal brain proteins in mothers of children with ASD have been described by several groups. To understand their pathologic significance, we developed a mouse model of maternal autoantibody related ASD (MAR-ASD) utilizing the peptide epitopes from human autoantibody reactivity patterns. Male and female offspring prenatally exposed to the salient maternal autoantibodies displayed robust deficits in social interactions and increased repetitive self-grooming behaviors as juveniles and adults. In the present study, neuroanatomical differences in adult MAR-ASD and control offspring were assessed via high-resolution ex vivo magnetic resonance imaging (MRI) at 6 months of age. Of interest, MAR-ASD mice displayed significantly larger total brain volume and of the 159 regions examined, 31 were found to differ significantly in absolute volume (mm3) at an FDR of <5%. Specifically, the absolute volumes of several white matter tracts, cortical regions, and basal nuclei structures were significantly increased in MAR-ASD animals. These phenomena were largely driven by female MAR-ASD offspring, as no significant differences were seen with either absolute or relative regional volume in male MAR-ASD mice. However, structural covariance analysis suggests network-level desynchronization in brain volume in both male and female MAR-ASD mice. Additionally, preliminary correlational analysis with behavioral data relates that volumetric increases in numerous brain regions of MAR-ASD mice were correlated with social interaction and repetitive self-grooming behaviors in a sex-specific manner. These results demonstrate significant sex-specific effects in brain size, regional relationships, and behavior for offspring prenatally exposed to MAR-ASD autoantibodies relative to controls.

Evaluation of a TrkB agonist on spatial and motor learning in the Ube3a mouse model of Angelman syndrome.

Angelman syndrome is a rare neurodevelopmental disorder caused by a mutation in the maternal allele of the gene Ube3a The primary symptoms of Angelman syndrome are severe cognitive deficits, impaired motor functions, and speech disabilities. Analogous phenotypes have been detected in young adult Ube3a mice. Here, we investigate cognitive phenotypes of Ube3a mice as compared to wild-type littermate controls at an older adult age. Water maze spatial learning, swim speed, and rotarod motor coordination and balance were impaired at 6 mo of age, as predicted. Based on previous findings of reduced brain-derived neurotrophic factor in Ube3a mice, a novel therapeutic target, the TrkB agonist 7,8-DHF, was interrogated. Semichronic daily treatment with 7,8-DHF, 5 mg/kg i.p., did not significantly improve the impairments in performance during the acquisition of the water maze hidden platform location in Ube3a mice, after training with either massed or spaced trials, and had no effect on the swim speed and rotarod deficits. Robust behavioral phenotypes in middle-aged Ube3a mice appear to result from continued motor decline. Our results suggest that motor deficits could offer useful outcome measures for preclinical testing of many pharmacological targets, with the goal of reducing symptoms in adults with Angelman syndrome.

Autism-specific maternal autoantibodies produce behavioral abnormalities in an endogenous antigen-driven mouse model of autism.

Immune dysregulation has been noted consistently in individuals with autism spectrum disorder (ASD) and their families, including the presence of autoantibodies reactive to fetal brain proteins in nearly a quarter of mothers of children with ASD versus <1% in mothers of typically developing children. Our lab recently identified the peptide epitope sequences on seven antigenic proteins targeted by these maternal autoantibodies. Through immunization with these peptide epitopes, we have successfully created an endogenous, antigen-driven mouse model that ensures a constant exposure to the salient autoantibodies throughout gestation in C57BL/6J mice. This exposure more naturally mimics what is observed in mothers of children with ASD. Male and female offspring were tested using a comprehensive sequence of behavioral assays, as well as measures of health and development highly relevant to ASD. We found that MAR-ASD male and female offspring had significant alterations in development and social interactions during dyadic play. Although 3-chambered social approach was not significantly different, fewer social interactions with an estrous female were noted in the adult male MAR-ASD animals, as well as reduced vocalizations emitted in response to social cues with robust repetitive self-grooming behaviors relative to saline treated controls. The generation of MAR-ASD-specific epitope autoantibodies in female mice prior to breeding created a model that demonstrates for the first time that ASD-specific antigen-induced maternal autoantibodies produced alterations in a constellation of ASD-relevant behaviors.

Behavioral Evaluation of Angelman Syndrome Mice at Older Ages.

Angelman syndrome is a neurodevelopmental disorder presenting with severe deficits in motor, speech, and cognitive abilities. The primary genetic cause of Angelman syndrome is a maternally transmitted mutation in the Ube3a gene, which has been successfully modeled in Ube3a mutant mice. Phenotypes have been extensively reported in young adult Ube3a mice. Because symptoms continue throughout life in Angelman syndrome, we tested multiple behavioral phenotypes of male Ube3a mice and WT littermate controls at older adult ages. Social behaviors on both the 3-chambered social approach and male-female social interaction tests showed impairments in Ube3a at 12 months of age. Anxiety-related scores on both the elevated plus-maze and the light ↔ dark transitions assays indicated anxiety-like phenotypes in 12 month old Ube3a mice. Open field locomotion parameters were consistently lower at 12 months. Reduced general exploratory locomotion at this age prevented the interpretation of an anxiety-like phenotype, and likely impacted social tasks. Robust phenotypes in middle-aged Ube3a mice appear to result from continued motor decline. Motor deficits may provide the best outcome measures for preclinical testing of pharmacological targets, towards reductions of symptoms in adults with Angelman syndrome.

Behavioral analyses of animal models of intellectual and developmental disabilities.

Intellectual and developmental disabilities (IDDs) are a common group of disorders that frequently share overlapping symptoms, including cognitive deficits, altered attention, seizures, impaired social interactions, and anxiety. The causes of these disorders are varied ranging from early prenatal/postnatal insults to genetic variants that either cause or are associated with an increased likelihood of an IDD. As many of the symptoms observed in individuals with IDDs are a manifestation of altered nervous system function resulting in altered behaviors, it should not be surprising that the field is very dependent upon in vivo model systems. This special issue of Neurobiology of Learning and Memory is focused on the methods and approaches that are being used to model and understand these disorders in mammals. While surveys by the Pew Foundation continue to find a high degree of confidence/trust in scientists by the public, several recent studies have documented issues with reproducibility in scientific publications. This special issue includes both primary research articles and review articles in which careful attention has been made to transparently report methods and use rigorous approaches to ensure reproducibility. Although there have been and will continue to be remarkable advances for treatment of subset of IDDs, it is clear that this field is still in its early stages. There is no doubt that the strategies being used to model IDDs will continue to evolve. We hope this special issue will support this evolution so that we can maintain the trust of the public and elected officials, and continue developing evidence-based approaches to new therapeutics.

Pathogenic WDFY3 variants cause neurodevelopmental disorders and opposing effects on brain size.

The underpinnings of mild to moderate neurodevelopmental delay remain elusive, often leading to late diagnosis and interventions. Here, we present data on exome and genome sequencing as well as array analysis of 13 individuals that point to pathogenic, heterozygous, mostly de novo variants in WDFY3 (significant de novo enrichment P = 0.003) as a monogenic cause of mild and non-specific neurodevelopmental delay. Nine variants were protein-truncating and four missense. Overlapping symptoms included neurodevelopmental delay, intellectual disability, macrocephaly, and psychiatric disorders (autism spectrum disorders/attention deficit hyperactivity disorder). One proband presented with an opposing phenotype of microcephaly and the only missense-variant located in the PH-domain of WDFY3. Findings of this case are supported by previously published data, demonstrating that pathogenic PH-domain variants can lead to microcephaly via canonical Wnt-pathway upregulation. In a separate study, we reported that the autophagy scaffolding protein WDFY3 is required for cerebral cortical size regulation in mice, by controlling proper division of neural progenitors. Here, we show that proliferating cortical neural progenitors of human embryonic brains highly express WDFY3, further supporting a role for this molecule in the regulation of prenatal neurogenesis. We present data on Wnt-pathway dysregulation in Wdfy3-haploinsufficient mice, which display macrocephaly and deficits in motor coordination and associative learning, recapitulating the human phenotype. Consequently, we propose that in humans WDFY3 loss-of-function variants lead to macrocephaly via downregulation of the Wnt pathway. In summary, we present WDFY3 as a novel gene linked to mild to moderate neurodevelopmental delay and intellectual disability and conclude that variants putatively causing haploinsufficiency lead to macrocephaly, while an opposing pathomechanism due to variants in the PH-domain of WDFY3 leads to microcephaly.

Hypothesis-driven investigations of diverse pharmacological targets in two mouse models of autism.

Autism spectrum disorder is a neurodevelopmental syndrome diagnosed primarily by persistent deficits in social interactions and communication, unusual sensory reactivity, motor stereotypies, repetitive behaviors, and restricted interests. No FDA-approved medical treatments exist for the diagnostic symptoms of autism. Here we interrogate multiple pharmacological targets in two distinct mouse models that incorporate well-replicated autism-relevant behavioral phenotypes. Compounds that modify inhibitory or excitatory neurotransmission were selected to address hypotheses based on previously published biological abnormalities in each model. Shank3B is a genetic model of a mutation found in autism and Phelan-McDermid syndrome, in which deficits in excitatory neurotransmission and synaptic plasticity have been reported. BTBR is an inbred strain model of forms of idiopathic autism in which reduced inhibitory neurotransmission and excessive mTOR signaling have been reported. The GABA-A receptor agonist gaboxadol significantly reduced repetitive self-grooming in three independent cohorts of BTBR. The TrkB receptor agonist 7,8-DHF improved spatial learning in Shank3B mice, and reversed aspects of social deficits in BTBR. CX546, a positive allosteric modulator of the glutamatergic AMPA receptor, and d-cycloserine, a partial agonist of the glycine site on the glutamatergic NMDA receptor, did not rescue aberrant behaviors in Shank3B mice. The mTOR inhibitor rapamycin did not ameliorate social deficits or repetitive behavior in BTBR mice. Comparison of positive and negative pharmacological outcomes, on multiple phenotypes, evaluated for replicability across independent cohorts, enhances the translational value of mouse models of autism for therapeutic discovery. GABA agonists present opportunities for personalized interventions to treat components of autism spectrum disorder. Autism Res 2019, 12: 401-421 © 2019 The Authors. Autism Research published by International Society for Autism Research published by Wiley Periodicals, Inc. LAY SUMMARY: Many of the risk genes for autism impair synapses, the connections between nerve cells in the brain. A drug that reverses the synaptic effects of a mutation could offer a precision therapy. Combining pharmacological and behavioral therapies could reduce symptoms and improve the quality of life for people with autism. Here we report reductions in repetitive behavior by a GABA-A receptor agonist, gaboxadol, and improvements in social and cognitive behaviors by a TrkB receptor agonist, in mouse models of autism.

Rigor and reproducibility in rodent behavioral research.

Behavioral neuroscience research incorporates the identical high level of meticulous methodologies and exacting attention to detail as all other scientific disciplines. To achieve maximal rigor and reproducibility of findings, well-trained investigators employ a variety of established best practices. Here we explicate some of the requirements for rigorous experimental design and accurate data analysis in conducting mouse and rat behavioral tests. Novel object recognition is used as an example of a cognitive assay which has been conducted successfully with a range of methods, all based on common principles of appropriate procedures, controls, and statistics. Directors of Rodent Core facilities within Intellectual and Developmental Disabilities Research Centers contribute key aspects of their own novel object recognition protocols, offering insights into essential similarities and less-critical differences. Literature cited in this review article will lead the interested reader to source papers that provide step-by-step protocols which illustrate optimized methods for many standard rodent behavioral assays. Adhering to best practices in behavioral neuroscience will enhance the value of animal models for the multiple goals of understanding biological mechanisms, evaluating consequences of genetic mutations, and discovering efficacious therapeutics.

Transcription Factor 2I Regulates Neuronal Development via TRPC3 in 7q11.23 Disorder Models.

Williams syndrome (WS) and 7q11.23 duplication syndrome (Dup7q11.23) are neurodevelopmental disorders caused by the deletion and duplication, respectively, of ~ 25 protein-coding genes on chromosome 7q11.23. The general transcription factor 2I (GTF2I, protein TFII-I) is one of these proteins and has been implicated in the neurodevelopmental phenotypes of WS and Dup7q11.23. Here, we investigated the effect of copy number alterations in Gtf2i on neuronal maturation and intracellular calcium entry mechanisms known to be associated with this process. Mice with a single copy of Gtf2i (Gtf2i+/Del) had increased axonal outgrowth and increased TRPC3-mediated calcium entry upon carbachol stimulation. In contrast, mice with 3 copies of Gtf2i (Gtf2i+/Dup) had decreases in axon outgrowth and in TRPC3-mediated calcium entry. The underlying mechanism was that TFII-I did not affect TRPC3 protein expression, while it regulated TRPC3 membrane translocation. Together, our results provide novel functional insight into the cellular mechanisms that underlie neuronal maturation in the context of the 7q11.23 disorders.

MeCP2 isoform e1 mutant mice recapitulate motor and metabolic phenotypes of Rett syndrome.

Mutations in the X-linked gene MECP2 cause the majority of Rett syndrome (RTT) cases. Two differentially spliced isoforms of exons 1 and 2 (MeCP2-e1 and MeCP2-e2) contribute to the diverse functions of MeCP2, but only mutations in exon 1, not exon 2, are observed in RTT. We previously described an isoform-specific MeCP2-e1-deficient male mouse model of a human RTT mutation that lacks MeCP2-e1 while preserving expression of MeCP2-e2. However, RTT patients are heterozygous females that exhibit delayed and progressive symptom onset beginning in late infancy, including neurologic as well as metabolic, immune, respiratory and gastrointestinal phenotypes. Consequently, we conducted a longitudinal assessment of symptom development in MeCP2-e1 mutant females and males. A delayed and progressive onset of motor impairments was observed in both female and male MeCP2-e1 mutant mice, including hind limb clasping and motor deficits in gait and balance. Because these motor impairments were significantly impacted by age-dependent increases in body weight, we also investigated metabolic phenotypes at an early stage of disease progression. Both male and female MeCP2-e1 mutants exhibited significantly increased body fat compared to sex-matched wild-type littermates prior to weight differences. Mecp2e1-/y males exhibited significant metabolic phenotypes of hypoactivity, decreased energy expenditure, increased respiratory exchange ratio, but decreased food intake compared to wild-type. Untargeted analysis of lipid metabolites demonstrated a distinguishable profile in MeCP2-e1 female mutant liver characterized by increased triglycerides. Together, these results demonstrate that MeCP2-e1 mutation in mice of both sexes recapitulates early and progressive metabolic and motor phenotypes of human RTT.

SynDIG4/Prrt1 Is Required for Excitatory Synapse Development and Plasticity Underlying Cognitive Function.

Altering AMPA receptor (AMPAR) content at synapses is a key mechanism underlying the regulation of synaptic strength during learning and memory. Previous work demonstrated that SynDIG1 (synapse differentiation-induced gene 1) encodes a transmembrane AMPAR-associated protein that regulates excitatory synapse strength and number. Here we show that the related protein SynDIG4 (also known as Prrt1) modifies AMPAR gating properties in a subunit-dependent manner. Young SynDIG4 knockout (KO) mice have weaker excitatory synapses, as evaluated by immunocytochemistry and electrophysiology. Adult SynDIG4 KO mice show complete loss of tetanus-induced long-term potentiation (LTP), while mEPSC amplitude is reduced by only 25%. Furthermore, SynDIG4 KO mice exhibit deficits in two independent cognitive assays. Given that SynDIG4 colocalizes with the AMPAR subunit GluA1 at non-synaptic sites, we propose that SynDIG4 maintains a pool of extrasynaptic AMPARs necessary for synapse development and function underlying higher-order cognitive plasticity.

R-Baclofen Reverses Cognitive Deficits and Improves Social Interactions in Two Lines of 16p11.2 Deletion Mice.

Human chromosome 16p11.2 microdeletion is among the most common gene copy number variations (CNVs) known to confer risk for intellectual disability (ID) and autism spectrum disorder (ASD) and affects an estimated 3 in 10 000 people. Caused by a single copy deletion of ~27 genes, 16p11.2 microdeletion syndrome is characterized by ID, impaired language, communication and socialization skills, and ASD. Studies in animal models where a single copy of the syntenic 16p11.2 region has been deleted have revealed morphological, behavioral, and electrophysiological abnormalities. Previous studies suggested the possibility of some overlap in the mechanisms of pathophysiology in 16p11.2 microdeletion syndrome and fragile X syndrome. Improvements in fragile X phenotypes have been observed following chronic treatment with R-baclofen, a selective agonist of GABAB receptors. We were therefore motivated to investigate the effects of chronic oral R-baclofen administration in two independently generated mouse models of 16p11.2 microdeletion syndrome. In studies performed across two independent laboratories, we found that chronic activation of GABAB receptors improved performance on a series of cognitive and social tasks known to be impaired in two different 16p11.2 deletion mouse models. Our findings suggest that R-baclofen may have clinical utility for some of the core symptoms of human 16p11.2 microdeletion syndrome.

Drug development for neurodevelopmental disorders: lessons learned from fragile X syndrome.

Neurodevelopmental disorders such as fragile X syndrome (FXS) result in lifelong cognitive and behavioural deficits and represent a major public health burden. FXS is the most frequent monogenic form of intellectual disability and autism, and the underlying pathophysiology linked to its causal gene, FMR1, has been the focus of intense research. Key alterations in synaptic function thought to underlie this neurodevelopmental disorder have been characterized and rescued in animal models of FXS using genetic and pharmacological approaches. These robust preclinical findings have led to the implementation of the most comprehensive drug development programme undertaken thus far for a genetically defined neurodevelopmental disorder, including phase IIb trials of metabotropic glutamate receptor 5 (mGluR5) antagonists and a phase III trial of a GABAB receptor agonist. However, none of the trials has been able to unambiguously demonstrate efficacy, and they have also highlighted the extent of the knowledge gaps in drug development for FXS and other neurodevelopmental disorders. In this Review, we examine potential issues in the previous studies and future directions for preclinical and clinical trials. FXS is at the forefront of efforts to develop drugs for neurodevelopmental disorders, and lessons learned in the process will also be important for such disorders.

Germline Chd8 haploinsufficiency alters brain development in mouse.

The chromatin remodeling gene CHD8 represents a central node in neurodevelopmental gene networks implicated in autism. We examined the impact of germline heterozygous frameshift Chd8 mutation on neurodevelopment in mice. Chd8+/del5 mice displayed normal social interactions with no repetitive behaviors but exhibited cognitive impairment correlated with increased regional brain volume, validating that phenotypes of Chd8+/del5 mice overlap pathology reported in humans with CHD8 mutations. We applied network analysis to characterize neurodevelopmental gene expression, revealing widespread transcriptional changes in Chd8+/del5 mice across pathways disrupted in neurodevelopmental disorders, including neurogenesis, synaptic processes and neuroimmune signaling. We identified a co-expression module with peak expression in early brain development featuring dysregulation of RNA processing, chromatin remodeling and cell-cycle genes enriched for promoter binding by Chd8, and we validated increased neuronal proliferation and developmental splicing perturbation in Chd8+/del5 mice. This integrative analysis offers an initial picture of the consequences of Chd8 haploinsufficiency for brain development.

Replicable in vivo physiological and behavioral phenotypes of the Shank3B null mutant mouse model of autism.

BACKGROUND: Autism spectrum disorder (ASD) is a clinically and biologically heterogeneous condition characterized by social, repetitive, and sensory behavioral abnormalities. No treatments are approved for the core diagnostic symptoms of ASD. To enable the earliest stages of therapeutic discovery and development for ASD, robust and reproducible behavioral phenotypes and biological markers are essential to establish in preclinical animal models. The goal of this study was to identify electroencephalographic (EEG) and behavioral phenotypes that are replicable between independent cohorts in a mouse model of ASD. The larger goal of our strategy is to empower the preclinical biomedical ASD research field by generating robust and reproducible behavioral and physiological phenotypes in animal models of ASD, for the characterization of mechanistic underpinnings of ASD-relevant phenotypes, and to ensure reliability for the discovery of novel therapeutics. Genetic disruption of the SHANK3 gene, a scaffolding protein involved in the stability of the postsynaptic density in excitatory synapses, is thought to be responsible for a relatively large number of cases of ASD. Therefore, we have thoroughly characterized the robustness of ASD-relevant behavioral phenotypes in two cohorts, and for the first time quantified translational EEG activity in Shank3B null mutant mice. METHODS: In vivo physiology and behavioral assays were conducted in two independently bred and tested full cohorts of Shank3B null mutant (Shank3B KO) and wildtype littermate control (WT) mice. EEG was recorded via wireless implanted telemeters for 7 days of baseline followed by 20 min of recording following pentylenetetrazol (PTZ) challenge. Behaviors relevant to the diagnostic and associated symptoms of ASD were tested on a battery of established behavioral tests. Assays were designed to reproduce and expand on the original behavioral characterization of Shank3B KO mice. Two or more corroborative tests were conducted within each behavioral domain, including social, repetitive, cognitive, anxiety-related, sensory, and motor categories of assays. RESULTS: Relative to WT mice, Shank3B KO mice displayed a dramatic resistance to PTZ seizure induction and an enhancement of gamma band oscillatory EEG activity indicative of enhanced inhibitory tone. These findings replicated in two separate cohorts. Behaviorally, Shank3B KO mice exhibited repetitive grooming, deficits in aspects of reciprocal social interactions and vocalizations, and reduced open field activity, as well as variable deficits in sensory responses, anxiety-related behaviors, learning and memory. CONCLUSIONS: Robust animal models and quantitative, replicable biomarkers of neural dysfunction are needed to decrease risk and enable successful drug discovery and development for ASD and other neurodevelopmental disorders. Complementary to the replicated behavioral phenotypes of the Shank3B mutant mouse is the new identification of a robust, translational in vivo neurophysiological phenotype. Our findings provide strong evidence for robustness and replicability of key translational phenotypes in Shank3B mutant mice and support the usefulness of this mouse model of ASD for therapeutic discovery.

Early motor phenotype detection in a female mouse model of Rett syndrome is improved by cross-fostering.

Rett syndrome (RTT) is an X-linked neurodevelopmental disorder caused by mutations in the gene encoding methyl CpG binding protein 2 (MeCP2) that occur sporadically in 1:10,000 female births. RTT is characterized by a period of largely normal development followed by regression in language and motor skills at 6-18 months of age. Mecp2 mutant mice recapitulate many of the clinical features of RTT, but the majority of behavioral assessments have been conducted in male Mecp2 hemizygous null mice as offspring of heterozygous dams. Given that RTT patients are predominantly female, we conducted a systematic analysis of developmental milestones, sensory abilities, and motor deficits, following the longitudinal decline of function from early postnatal to adult ages in female Mecp2 heterozygotes of the conventional Bird line (Mecp2tm1.1bird-/+), as compared to their female wildtype littermate controls. Further, we assessed the impact of postnatal maternal environment on developmental milestones and behavioral phenotypes. Cross-fostering to CD1 dams accelerated several developmental milestones independent of genotype, and induced earlier onset of weight gain in adult female Mecp2tm1.1bird-/+ mice. Cross-fostering improved the sensitivity of a number of motor behaviors that resulted in observable deficits in Mecp2tm1.1bird-/+ mice at much earlier (6-7 weeks) ages than were previously reported (6-9 months). Our findings indicate that female Mecp2tm1.1bird-/+ mice recapitulate many of the motor aspects of RTT syndrome earlier than previously appreciated. In addition, rearing conditions may impact the phenotypic severity and improve the ability to detect genotype differences in female Mecp2 mutant mice.

Behavioral Phenotyping Assays for Genetic Mouse Models of Neurodevelopmental, Neurodegenerative, and Psychiatric Disorders.

Animal models offer heuristic research tools to understand the causes of human diseases and to identify potential treatments. With rapidly evolving genetic engineering technologies, mutations identified in a human disorder can be generated in the mouse genome. Phenotypic outcomes of the mutation are then explicated to confirm hypotheses about causes and to discover effective therapeutics. Most neurodevelopmental, neurodegenerative, and psychiatric disorders are diagnosed primarily by their prominent behavioral symptoms. Mouse behavioral assays analogous to the human symptoms have been developed to analyze the consequences of mutations and to evaluate proposed therapeutics preclinically. Here we describe the range of mouse behavioral tests available in the established behavioral neuroscience literature, along with examples of their translational applications. Concepts presented have been successfully used in other species, including flies, worms, fish, rats, pigs, and nonhuman primates. Identical strategies can be employed to test hypotheses about environmental causes and gene × environment interactions.