Developmental disruption to the cortical transcriptome and synaptosome in a model of SETD1A loss-of-function

An ace in the hole? Opportunities and limits of using mice to understand schizophrenia neurobiology

In applying model organisms to study the neurobiology of mental disorders, rodents offer unique potential for probing, with high spatiotemporal resolution, the neural and molecular mechanisms underlying behavior in a mammalian system. Furthermore, investigators can wield exceptional power to manipulate genes, molecules, and circuits in mice to pin down causal relationships. While these advantages have allowed us to understand much more deeply than ever before the brain mechanisms regulating complex behaviors, the impact of rodent models on developing therapeutic strategies for psychiatric disorders has remained thus far limited. Herein, we will discuss the opportunities and limits of using mouse models in the context of schizophrenia, a complex psychiatric disorder with strong genetic basis that poses various unmet clinical needs calling out for basic science research. We review approaches for employing behavioral, genetic, and circuit-based methods in rodents to inform schizophrenia symptomatology, pathophysiology, and, ultimately, treatment.

A human-specific enhancer fine-tunes radial glia potency and corticogenesis

Humans have evolved an extraordinarily expanded and complex cerebral cortex associated with developmental and gene regulatory modifications1-3. Human accelerated regions (HARs) are highly conserved DNA sequences with human-specific nucleotide substitutions. Although there are thousands of annotated HARs, their functional contribution to species-specific cortical development remains largely unknown4,5. HARE5 is a HAR transcriptional enhancer of the WNT signalling receptor Frizzled8 that is active during brain development6. Here, using genome-edited mouse (Mus musculus, Mm) and primate models, we demonstrated that human (Homo sapiens, Hs) HARE5 fine-tunes cortical development and connectivity by controlling the proliferative and neurogenic capacities of neural progenitor cells. Hs-HARE5 knock-in mice have significantly enlarged neocortices, containing more excitatory neurons. By measuring neural dynamics in vivo, we showed that these anatomical features result in increased functional independence between cortical regions. We assessed underlying developmental mechanisms using fixed and live imaging, lineage analysis and single-cell RNA sequencing. We discovered that Hs-HARE5 modifies radial glial cell behaviour, with increased self-renewal at early developmental stages, followed by expanded neurogenic potential. Using genome-edited human and chimpanzee (Pan troglodytes, Pt) neural progenitor cells and cortical organoids, we showed that four human-specific variants of Hs-HARE5 drive increased enhancer activity that promotes progenitor proliferation. Finally, we showed that Hs-HARE5 increased progenitor proliferation by amplifying canonical WNT signalling. These findings illustrate how small changes in regulatory DNA can directly affect critical signalling pathways to modulate brain development. Our study uncovered new functions of HARs as key regulatory elements crucial for the expansion and complexity of the human cerebral cortex.

O-GlcNAc transferase congenital disorder of glycosylation (OGT-CDG): Potential mechanistic targets revealed by evaluating the OGT interactome

O-GlcNAc transferase (OGT) is the sole enzyme responsible for the post-translational modification of O-GlcNAc on thousands of target nucleocytoplasmic proteins. To date, nine variants of OGT that segregate with OGT Congenital Disorder of Glycosylation (OGT-CDG) have been reported and characterized. Numerous additional variants have been associated with OGT-CDG, some of which are currently undergoing investigation. This disorder primarily presents with global developmental delay and intellectual disability (ID), alongside other variable neurological features and subtle facial dysmorphisms in patients. Several hypotheses aim to explain the etiology of OGT-CDG, with a prominent hypothesis attributing the pathophysiology of OGT-CDG to mutations segregating with this disorder disrupting the OGT interactome. The OGT interactome consists of thousands of proteins, including substrates as well as interactors that require noncatalytic functions of OGT. A key aim in the field is to identify which interactors and substrates contribute to the primarily neural-specific phenotype of OGT-CDG. In this review, we will discuss the heterogenous phenotypic features of OGT-CDG seen clinically, the variable biochemical effects of mutations associated with OGT-CDG, and the use of animal models to understand this disorder. Furthermore, we will discuss how previously identified OGT interactors causal for ID provide mechanistic targets for investigation that could explain the dysregulated gene expression seen in OGT-CDG models. Identifying shared or unique altered pathways impacted in OGT-CDG patients will provide a better understanding of the disorder as well as potential therapeutic targets.

Sex-dependent effects of Setd1a haploinsufficiency on development and adult behaviour

Loss of function (LoF) mutations affecting the histone methyl transferase SETD1A are implicated in the aetiology of a range of neurodevelopmental disorders including schizophrenia. We examined indices of development and adult behaviour in a mouse model of Setd1a haploinsufficiency, revealing a complex pattern of sex-related differences spanning the pre- and post-natal period. Specifically, male Setd1a+/- mice had smaller placentae at E11.5 and females at E18.5 without any apparent changes in foetal size. In contrast, young male Setd1a+/- mice had lower body weight and showed enhanced growth, leading to equivalent weights by adulthood. Embryonic whole brain RNA-seq analysis revealed expression changes that were significantly enriched for mitochondria-related genes in Setd1a+/ samples. In adulthood, we found enhanced acoustic startle responding in male Setd1a+/- mice which was insentitive to the effects of risperidone, but not haloperidol, both commonly used antipsychotic drugs. We also observed reduced pre-pulse inhibition of acoustic startle, a schizophrenia-relevant phenotype, in both male and female Setd1a+/- mice which could not be rescued by either drug. In the open field and elevated plus maze tests of anxiety, Setd1a haplosufficiency led to more anxiogenic behaviour in both sexes, whereas there were no differences in general motoric ability and memory. Thus, we find evidence for changes in a number of phenotypes which strengthen the support for the use of Setd1a haploinsufficient mice as a model for the biological basis of schizophrenia. Furthermore, our data point towards possible underpinning neural and developmental mechanisms that may be subtly different between the sexes.

SETD1A variant-associated psychosis: A systematic review of the clinical literature and description of two new cases

OBJECTIVE

SETD1A encodes a histone methyltransferase involved in various cell cycle regulatory processes. Loss-of-function SETD1A variants have been associated with numerous neurodevelopmental phenotypes, including intellectual disability and schizophrenia. While the association between rare coding variants in SETD1A and schizophrenia has achieved genome-wide significance by rare variant burden testing, only a few studies have described the psychiatric phenomenology of such individuals in detail. This systematic review and case report aims to characterize the neurodevelopmental and psychiatric phenotypes of SETD1A variant-associated schizophrenia.

METHODS

A PubMed search was completed in July 2022 and updated in May 2023. Only studies that reported individuals with a SETD1A variant as well as a primary psychotic disorder were ultimately included. Additionally, another two previously unpublished cases of SETD1A variant-associated psychosis from our own sequencing cohort are described.

RESULTS

The search yielded 32 articles. While 15 articles met inclusion criteria, only five provided case descriptions. In total, phenotypic information was available for 11 individuals, in addition to our own two unpublished cases. Our findings suggest that although individuals with SETD1A variant-associated schizophrenia may share a number of common features, phenotypic variability nonetheless exists. Moreover, although such individuals may exhibit numerous other neurodevelopmental features suggestive of the syndrome, their psychiatric presentations appear to be similar to those of general schizophrenia populations.

CONCLUSIONS

Loss-of-function SETD1A variants may underlie the development of psychosis in a small percentage of individuals with schizophrenia. Identifying such individuals may become increasingly important, given the potential for advances in precision medicine treatment approaches.

Novel mutation in the SETD1A gene in a newborn patient associating with congenital airway and heart defeats: A case report

RATIONALE

Congenital malformations are commonly associated with genetic disorders in infants and children.

PATIENT CONCERNS

A 13-day-old male infant was admitted to our hospital presenting with aggravated dyspnea and characteristic facial and body features. Examinations during hospitalization found congenital bronchomalacia and heart defects including atrial septal defect, patent ductus arteriosus, and pulmonary hypertension, congenital laryngeal stridor, and tracheal stenosis.

DIAGNOSIS

Considering complicated clinical manifestations, the Trio Whole Exon Sequencing test was run to screen for any hereditary diseases and found a heterozygous pathogenic mutation in SET domain containing 1A (SETD1A) gene (c.2096T > A; p. Leu699Ter, 1099), which was a de novo mutation.

INTERVENTION

The patient was given amoxicillin clavulanate potassium for antibiotic, fibro bronchoscope lavage and other symptomatic support therapy, and referred to the department of Cardiac Surgery for arterial catheter ligation.

OUTCOMES

The patient was discharged after postoperative recovery without shunt. In the following 2 years, he was admitted to hospital multiple times during to infectious pneumonia.

LESSONS

SETD1A gene mutation is commonly associated with neuropsychiatric disorders. This is the first reported case with a novel mutation of SETD1A gene along with new associated phenotypes. Our results broaden the genotypic and phenotypes spectrum of SETD1A gene mutation in infant patients.

The role of histone modifications: from neurodevelopment to neurodiseases

Epigenetic regulatory mechanisms, including DNA methylation, histone modification, chromatin remodeling, and microRNA expression, play critical roles in cell differentiation and organ development through spatial and temporal gene regulation. Neurogenesis is a sophisticated and complex process by which neural stem cells differentiate into specialized brain cell types at specific times and regions of the brain. A growing body of evidence suggests that epigenetic mechanisms, such as histone modifications, allow the fine-tuning and coordination of spatiotemporal gene expressions during neurogenesis. Aberrant histone modifications contribute to the development of neurodegenerative and neuropsychiatric diseases. Herein, recent progress in understanding histone modifications in regulating embryonic and adult neurogenesis is comprehensively reviewed. The histone modifications implicated in neurodegenerative and neuropsychiatric diseases are also covered, and future directions in this area are provided.