Abnormal maternal behavior, altered sociability, and impaired serotonin metabolism in Rai1-transgenic mice

Dosage-sensitive genes in autism spectrum disorders: From neurobiology to therapy

Autism spectrum disorders (ASDs) are a group of heterogenous neurodevelopmental disorders affecting 1 in 59 children. Syndromic ASDs are commonly associated with chromosomal rearrangements or dosage imbalance involving a single gene. Many of these genes are dosage-sensitive and regulate transcription, protein homeostasis, and synaptic function in the brain. Despite vastly different molecular perturbations, syndromic ASDs share core symptoms including social dysfunction and repetitive behavior. However, each ASD subtype has a unique pathogenic mechanism and combination of comorbidities that require individual attention. We have learned a great deal about how these dosage-sensitive genes control brain development and behaviors from genetically-engineered mice. Here we describe the clinical features of eight monogenic neurodevelopmental disorders caused by dosage imbalance of four genes, as well as recent advances in using genetic mouse models to understand their pathogenic mechanisms and develop intervention strategies. We propose that applying newly developed quantitative molecular and neuroscience technologies will advance our understanding of the unique neurobiology of each disorder and enable the development of personalized therapy.

Serotonin and motherhood: From molecules to mood

Emerging research points to a valuable role of the monoamine neurotransmitter, serotonin, in the display of maternal behaviors and reproduction-associated plasticity in the maternal brain. Serotonin is also implicated in the pathophysiology of numerous affective disorders and likely plays an important role in the pathophysiology of maternal mental illness. Therefore, the main goals of this review are to detail: (1) how the serotonin system of the female brain changes across pregnancy and postpartum; (2) the role of the central serotonergic system in maternal caregiving and maternal aggression; and (3) how the serotonin system and selective serotonin reuptake inhibitor medications (SSRIs) are involved in the treatment of maternal mental illness. Although there is much work to be done, studying the central serotonin system's multifaceted role in the maternal brain is vital to our understanding of the processes governing matrescence and the maintenance of motherhood.

Neurofilament light interaction with GluN1 modulates neurotransmission and schizophrenia-associated behaviors

Neurofilament (NFL) proteins have recently been found to play unique roles in synapses. NFL is known to interact with the GluN1 subunit of N-methyl-D-aspartic acid (NMDAR) and be reduced in schizophrenia though functional consequences are unknown. Here we investigated whether the interaction of NFL with GluN1 modulates synaptic transmission and schizophrenia-associated behaviors. The interaction of NFL with GluN1 was assessed by means of molecular, pharmacological, electrophysiological, magnetic resonance spectroscopy (MRS), and schizophrenia-associated behavior analyses. NFL deficits cause an NMDAR hypofunction phenotype including abnormal hippocampal function, as seen in schizophrenia. NFL-/- deletion in mice reduces dendritic spines and GluN1 protein levels, elevates ubiquitin-dependent turnover of GluN1 and hippocampal glutamate measured by MRS, and depresses hippocampal long-term potentiation. NMDAR-related behaviors are also impaired, including pup retrieval, spatial and social memory, prepulse inhibition, night-time activity, and response to NMDAR antagonist, whereas motor deficits are minimal. Importantly, partially lowering NFL in NFL+/- mice to levels seen regionally in schizophrenia, induced similar but milder NMDAR-related synaptic and behavioral deficits. Our findings support an emerging view that central nervous system neurofilament subunits including NFL in the present report, serve distinctive, critical roles in synapses relevant to neuropsychiatric diseases.

HP1BP3 expression determines maternal behavior and offspring survival

Maternal care is an indispensable behavioral component necessary for survival and reproductive success in mammals, and postpartum maternal behavior is mediated by an incompletely understood complex interplay of signals including effects of epigenetic regulation. We approached this issue using our recently established mice with targeted deletion of heterochromatin protein 1 binding protein 3 (HP1BP3), which we found to be a novel epigenetic repressor with critical roles in postnatal growth. Here, we report a dramatic reduction in the survival of pups born to Hp1bp3(-/-) deficient mouse dams, which could be rescued by co-fostering with wild-type dams. Hp1bp3(-/-) females failed to retrieve both their own pups and foster pups in a pup retrieval test, and showed reduced anxiety-like behavior in the open-field and elevated-plus-maze tests. In contrast, Hp1bp3(-/-) females showed no deficits in behaviors often associated with impaired maternal care, including social behavior, depression, motor coordination and olfactory capability; and maintained unchanged anxiety-associated hallmarks such as cholinergic status and brain miRNA profiles. Collectively, our results suggest a novel role for HP1BP3 in regulating maternal and anxiety-related behavior in mice and call for exploring ways to manipulate this epigenetic process.

RAI1 Overexpression Promotes Altered Circadian Gene Expression and Dyssomnia in Potocki-Lupski Syndrome

Retinoic acid induced 1 ( RAI1 ) encodes a dosage-sensitive gene that when haploinsufficient results in Smith-Magenis syndrome (SMS) and when overexpressed results in Potocki-Lupski syndrome (PTLS). Phenotypic and molecular evidence illustrates that haploinsufficiency of RAI1 disrupts circadian rhythm through the dysregulation of the master circadian regulator, circadian locomotor output cycles kaput ( CLOCK) , and other core circadian components, contributing to prominent sleep disturbances in SMS. However, the phenotypic and molecular characterization of sleep features in PTLS has not been elucidated. Using the Pittsburgh Sleep Quality Index (PSQI), caregivers of 15 school-aged children with PTLS reported difficulties in initiating sleep. Indeed, more than 70% of individuals manifested moderate to severe sleep latency, as defined by the PSQI. Moreover, these individuals manifested difficulties in sleep maintenance, with middle of the night and early morning awakenings. When assessing daytime sleepiness through the Epworth Sleepiness Scale, approximately 21% of the individuals manifested excessive daytime somnolence. This indicates that mild dyssomnia characterizes the majority of the sleep phenotype, with occasionally problematic daytime somnolence, a phenotype different than that expressed by individuals with SMS, where daytime sleepiness is a chronic problem. Gene expression analysis of the core circadian machinery in the hypothalamus of the PTLS mouse model ( Rai1 -Tg) found significant dysregulation of the transcriptional activators, Clock and Arntl , and the transcriptional repressors, Per1-3 and Cry1/2 , during both light and dark phases. These findings suggest a partial loss of circadian entrainment typically evoked by environmental photic cues. Examination of circadian clock gene expression in the Rai1- Tg mouse heart, liver, and kidney found unchanged expression of Clock and most of its downstream targets during both light and dark phases, suggesting an asynchronized circadian rhythm. Furthermore, examination of circadian gene expression in synchronized PTLS lymphoblasts revealed reduced transcripts of the Period ( PER1-3 ) family and normal expression of CRY1/2 . The finding that central circadian gene expression was altered while many peripheral circadian components were intact suggests a tissue-specific circadian uncoupling of the circadian machinery due to Rai1 overexpression. Overall, our results demonstrate that overexpression of RAI1 results in sleep deficiencies in individuals with PTLS due to a lack of properly regulated circadian machinery gene expression and highlight the importance of evaluating sleep concerns in individuals with PTLS.

Yin-yang actions of histone methylation regulatory complexes in the brain

Dysregulation of histone methylation has emerged as a major driver of neurodevelopmental disorders including intellectual disabilities and autism spectrum disorders. Histone methyl writer and eraser enzymes generally act within multisubunit complexes rather than in isolation. However, it remains largely elusive how such complexes cooperate to achieve the precise spatiotemporal gene expression in the developing brain. Histone H3K4 methylation (H3K4me) is a chromatin signature associated with active gene-regulatory elements. We review a body of literature that supports a model in which the RAI1-containing H3K4me writer complex counterbalances the LSD1-containing H3K4me eraser complex to ensure normal brain development. This model predicts H3K4me as the nexus of previously unrelated neurodevelopmental disorders.

Neurodevelopmental Disorders Associated with Abnormal Gene Dosage: Smith-Magenis and Potocki-Lupski Syndromes

Smith-Magenis syndrome (SMS) and Potocki-Lupski syndrome (PTLS) are reciprocal contiguous gene syndromes within the well-characterized 17p11.2 region. Approximately 3.6 Mb microduplication of 17p11.2, known as PTLS, represents the mechanistically predicted homologous recombination reciprocal of the SMS microdeletion, both resulting in multiple congenital anomalies. Mouse model studies have revealed that the retinoic acid-inducible 1 gene (RAI1) within the SMS and PTLS critical genomic interval is the dosage-sensitive gene responsible for the major phenotypic features in these disorders. Even though PTLS and SMS share the same genomic region, clinical manifestations and behavioral issues are distinct and in fact some mirror traits may be on opposite ends of a given phenotypic spectrum. We describe the neurobehavioral phenotypes of SMS and PTLS patients during different life phases as well as clinical guidelines for diagnosis and a multidisciplinary approach once diagnosis is confirmed by array comparative genomic hybridization or RAI1 gene sequencing. The main goal is to increase awareness of these rare disorders because an earlier diagnosis will lead to more timely developmental intervention and medical management which will improve clinical outcome.

Retinoic acid induced-1 (Rai1) regulates craniofacial and brain development in Xenopus

Retinoic acid induced-1 (RAI1) is an important yet understudied histone code reader that when mutated in humans results in Smith-Magenis syndrome (SMS), a neurobehavioral disorder accompanied by signature craniofacial abnormalities. Despite previous studies in mouse and human cell models, very little is known about the function of RAI1 during embryonic development. In the present study, we have turned to the model vertebrates Xenopus laevis and Xenopus tropicalis to better understand the developmental roles of Rai1. First we demonstrate that the Rai1 protein sequence is conserved in frogs, especially in known functional domains. By in situ hybridization we revealed expression of rai1 in the developing craniofacial tissues and the nervous system. Knockdown of Rai1 using antisense morpholinos resulted in defects in the developing brain and face. In particular, Rai1 morphants display midface hypoplasia and malformed mouth shape analogous to defects in humans with SMS. These craniofacial defects were accompanied with aberrant neural crest migration and reduction in the size of facial cartilage elements. Rai1 morphants also had defects in axon patterns and decreased forebrain ventricle size. Such brain defects correlated with a decrease in the neurotrophic factor, bdnf, and increased forebrain apoptosis. Our results emphasize a critical role of Rai1 for normal neural and craniofacial development, and further the current understanding of potential mechanisms that cause SMS.

Diametric gene-dosage effects as windows into neurogenetic architecture

Gene expression can be modulated in two opposite directions, towards higher or lower amounts of product. How do diametric changes in gene dosage influence neurological development and function? Recent studies of transgenic and knockout mouse models, genomic copy-number variants, imprinted-gene expression alterations, and sex-chromosome aneuploidies are revealing examples of 'mirror-extreme' brain and behavior phenotypes, which provide unique insights into neurodevelopmental architecture. These convergent studies quantitatively connect gene dosages with specific trajectories and outcomes, with important implications for the experimental dissection of normal neurological functions, the genetic analysis of psychiatric disorders, the development of pharmacological therapies, and mechanisms for the evolution of human brain and behavior.

Why the maternal brain?

In the rat, the change from a virgin/nulliparous female to the maternal animal takes place at many levels. A subtle developmental wave washes over the female nervous system and transforms her from largely self-centred to offspring-directed, from personal care and protection to care of genetically-related offspring, from indifference to ardour. Such change is preceded by substantial and apparently permanent neural alterations, the depth of which results in the maternal brain, and is the basis of the present review. The neuroplasticity of pregnancy, inherent to the female brain and, we believe, representative of the full expression of the female nervous system's capacity, is a result of significant hormonal and other neurochemical actions. It results in the striking brain changes that are associated with, and necessary for, successful reproduction. We discuss some of these changes and their ramifications. Collectively, they represent the culmination of mammalian evolution and have led to the development of the social brain characteristic of higher orders of mammal, including the human. We also examine different facets of the maternal brain, beginning with a review of the genes involved in maternal behaviour, and in the subsequent 'expression' of the maternal brain. We next discuss olfaction and the manner in which this major sense draws from the rich sensory milieu of the mother to regulate and support maternal behaviour. Last, we discuss the 'whys' of maternal behaviour, a theoretical foray into the reasons for such substantial maternal brain alterations. We focus on the male's potential role as the raison d'etre for the manifest alterations in his mate's brain. In the end, it is clear that the female brain undergoes a significant reorganisation en route to motherhood, the results of which are deep and enduring.

Molecular analysis of the Retinoic Acid Induced 1 gene (RAI1) in patients with suspected Smith-Magenis syndrome without the 17p11.2 deletion

Smith-Magenis syndrome (SMS) is a complex neurobehavioral disorder characterized by multiple congenital anomalies. The syndrome is primarily ascribed to a ∼3.7 Mb de novo deletion on chromosome 17p11.2. Haploinsufficiency of multiple genes likely underlies the complex clinical phenotype. RAI1 (Retinoic Acid Induced 1) is recognized as a major gene involved in the SMS phenotype. Extensive genetic and clinical analyses of 36 patients with SMS-like features, but without the 17p11.2 microdeletion, yielded 10 patients with RAI1 variants, including 4 with de novo deleterious mutations, and 6 with novel missense variants, 5 of which were familial. Haplotype analysis showed two major RAI1 haplotypes in our primarily Caucasian cohort; the novel RAI1 variants did not occur in a preferred haplotype. RNA analysis revealed that RAI1 mRNA expression was significantly decreased in cells of patients with the common 17p11.2 deletion, as well as in those with de novo RAI1 variants. Expression levels varied in patients with familial RAI1 variants and in non-17p11.2 deleted patients without identified RAI1 defects. No correlation between SNP haplotype and RAI1 expression was found. Two clinical features, ocular abnormalities and polyembolokoilomania (object insertion), were significantly correlated with decreased RAI1 expression. While not significantly correlated, the presence of hearing loss, seizures, hoarse voice, childhood onset of obesity and specific behavioral aspects and the absence of immunologic abnormalities and cardiovascular or renal structural anomalies, appeared to be specific for the de novo RAI1 subgroup. Recognition of the combination of these features will assist in referral for RAI1 analysis of patients with SMS-like features without detectable microdeletion of 17p11.2. Moreover, RAI1 expression emerged as a genetic target for development of therapeutic interventions for SMS.

Mouse models of genomic syndromes as tools for understanding the basis of complex traits: an example with the smith-magenis and the potocki-lupski syndromes

Each human's genome is distinguished by extra and missing DNA that can be “benign” or powerfully impact everything from development to disease. In the case of genomic disorders DNA rearrangements, such as deletions or duplications, correlate with a clinical specific phenotype. The clinical presentations of genomic disorders were thought to result from altered gene copy number of physically linked dosage sensitive genes. Genomic disorders are frequent diseases (~1 per 1,000 births). Smith-Magenis syndrome (SMS) and Potocki-Lupski syndrome (PTLS) are genomic disorders, associated with a deletion and a duplication, of 3.7 Mb respectively, within chromosome 17 band p11.2. This region includes 23 genes. Both syndromes have complex and distinctive phenotypes including multiple congenital and neurobehavioral abnormalities. Human chromosome 17p11.2 is syntenic to the 32-34 cM region of murine chromosome 11. The number and order of the genes are highly conserved. In this review, we will exemplify how genomic disorders can be modeled in mice and the advantages that such models can give in the study of genomic disorders in particular and gene copy number variation (CNV) in general. The contributions of the SMS and PTLS animal models in several aspects ranging from more specific ones, as the definition of the clinical aspects of the human clinical spectrum, the identification of dosage sensitive genes related to the human syndromes, to the more general contributions as the definition of genetic locus impacting obesity and behavior and the elucidation of general mechanisms related to the pathogenesis of gene CNV are discussed.

Retinoic Acid Induced 1, RAI1: A Dosage Sensitive Gene Related to Neurobehavioral Alterations Including Autistic Behavior

Genomic structural changes, such as gene Copy Number Variations (CNVs) are extremely abundant in the human genome. An enormous effort is currently ongoing to recognize and catalogue human CNVs and their associations with abnormal phenotypic outcomes. Recently, several reports related neuropsychiatric diseases (i.e. autism spectrum disorders, schizophrenia, mental retardation, behavioral problems, epilepsy) with specific CNV. Moreover, for some conditions, both the deletion and duplication of the same genomic segment are related to the phenotype. Syndromes associated with CNVs (microdeletion and microduplication) have long been known to display specific neurobehavioral traits. It is important to note that not every gene is susceptible to gene dosage changes and there are only a few dosage sensitive genes. Smith-Magenis (SMS) and Potocki-Lupski (PTLS) syndromes are associated with a reciprocal microdeletion and microduplication within chromosome 17p11.2. in humans. The dosage sensitive gene responsible for most phenotypes in SMS has been identified: the Retinoic Acid Induced 1 (RAI1). Studies on mouse models and humans suggest that RAI1 is likely the dosage sensitive gene responsible for clinical features in PTLS. In addition, the human RAI1 gene has been implicated in several neurobehavioral traits as spinocerebellar ataxia (SCA2), schizophrenia and non syndromic autism. In this review we discuss the evidence of RAI1 as a dosage sensitive gene, its relationship with different neurobehavioral traits, gene structure and mutations, and what is known about its molecular and cellular function, as a first step in the elucidation of the mechanisms that relate dosage sensitive genes with abnormal neurobehavioral outcomes.

Smith–Magenis syndrome: haploinsufficiency of RAI1 results in altered gene regulation in neurological and metabolic pathways

Smith–Magenis syndrome (SMS) is a complex neurobehavioural disorder characterised by intellectual disability, self-injurious behaviours, sleep disturbance, obesity, and craniofacial and skeletal anomalies. Diagnostic strategies are focused towards identification of a 17p11.2 microdeletion encompassing the gene RAI1 (retinoic acid induced 1) or a mutation of RAI1. Molecular evidence shows that most SMS features are due to RAI1 haploinsufficiency, whereas variability and severity are modified by other genes in the 17p11.2 region for 17p11.2 deletion cases. The functional role of RAI1 is not completely understood, but it is probably a transcription factor acting in several different biological pathways that are dysregulated in SMS. Functional studies based on the hypothesis that RAI1 acts through phenotype-specific pathways involving several downstream genes have shown that RAI1 gene dosage is crucial for normal regulation of circadian rhythm, lipid metabolism and neurotransmitter function. Here, we review the clinical and molecular features of SMS and explore more recent studies supporting possible therapeutic strategies for behavioural management.