Impaired neurogenesis alters brain biomechanics in a neuroprogenitor-based genetic subtype of congenital hydrocephalus

Unveiling EIF5A2: A multifaceted player in cellular regulation, tumorigenesis and drug resistance

The eukaryotic initiation factor 5A2 gene (EIF5A2) is a highly conserved and multifunctional gene that significantly influences various cellular processes, including translation elongation, RNA binding, ribosome binding, protein binding and post-translational modifications. Overexpression of EIF5A2 is frequently observed in multiple cancers, where it functions as an oncoprotein. Additionally, EIF5A2 is implicated in drug resistance through the regulation of various molecular pathways. In the review, we describe the structure and functions of EIF5A2 in normal cells and its role in tumorigenesis. We also elucidate the molecular mechanisms associated with EIF5A2 in the context of tumorigenesis and drug resistance. We propose that the biological roles of EIF5A2 in regulating diverse cellular processes and tumorigenesis are clinically significant and warrant further investigation.

Precision medicine in the pediatric and neonatal intensive care units through genomics

PURPOSE OF REVIEW

Genome-wide sequencing technologies have revolutionized the understanding of human disorders and advanced precision medicine, especially for pediatric disorders. Here, we discuss the utility of genomic technologies in advancing the care of children admitted to the pediatric and neonatal intensive care units.

RECENT FINDINGS

Rapid molecular diagnosis permitted by genomic medicine has yielded clinically actionable findings that influence decision-making and facilitate timely therapeutic interventions. Identifying a genetic association provides a causal anchor to understanding disease biology at the single nucleotide resolution, revealing hidden biological heterogeneity that may be obscured by traditional imaging, laboratory, and pathological workup. The importance of a genetic diagnosis is further highlighted by the promise of gene therapy to correct the underlying genetic perturbation, as evidenced by the recent emergence of FDA-approved gene therapies for childhood genetic conditions.

SUMMARY

We predict that whole-genome sequencing, in conjunction with other omic technologies, will become critical diagnostic adjuncts in the clinical workup of critically ill children.

De novo variants disrupt an LDB1-regulated transcriptional network in congenital ventriculomegaly

Congenital hydrocephalus, characterized by cerebral ventriculomegaly, is among the most common and least understood paediatric neurosurgical disorders. We have identified, in the largest assembled cerebral ventriculomegaly cohort (2697 parent-proband trios), an exome-wide significant enrichment of protein-altering de novo variants in LDB1 (P = 1.11 × 10-15). Eight unrelated patients with ventriculomegaly, developmental delay and dysmorphic features harboured loss-of-function de novo variants that truncate carboxy-terminal LIM interaction domain of LDB1, which regulates assembly of LIM homeodomain-containing transcriptional modulators. Integrative multiomic analyses suggest that LDB1 is a key transcriptional regulator in ventricular neuroprogenitors through its binding to LIM-homeodomain proteins, including SMARCC1 and ARID1B. Indeed, LIM-homeodomain-containing genes carry a disproportionate burden of protein-damaging de novo variants in our cohort, with SMARCC1 (P = 5.83 × 10-9) and ARID1B (P = 1.80 × 10-17) surpassing exome-wide significance thresholds. These data identify LBD1 as a novel neurodevelopmental disorder gene and suggest that an LDB1-regulated transcriptional programme is essential for human brain morphogenesis.

Impaired primitive erythropoiesis and defective vascular development in Trim71-KO embryos

The transition of an embryo from gastrulation to organogenesis requires precisely coordinated changes in gene expression, but the underlying mechanisms remain unclear. The RNA-binding protein Trim71 is essential for development and serves as a potent regulator of post-transcriptional gene expression. Here, we show that global deficiency of Trim71 induces severe defects in mesoderm-derived cells at the onset of organogenesis. Murine Trim71-KO embryos displayed impaired primitive erythropoiesis, yolk sac vasculature, heart function, and circulation, explaining the embryonic lethality of these mice. Tie2 Cre Trim71 conditional knockout did not induce strong defects, showing that Trim71 expression in endothelial cells and their immediate progenitors is dispensable for embryonic survival. scRNA-seq of E7.5 global Trim71-KO embryos revealed that transcriptomic changes arise already at gastrulation, showing a strong up-regulation of the mesodermal pioneer transcription factor Eomes. We identify Eomes as a direct target of Trim71-mediated mRNA repression via the NHL domain, demonstrating a functional link between these important regulatory genes. Taken together, our data suggest that Trim71-dependent control of gene expression at gastrulation establishes a framework for proper development during organogenesis.

Perturbed cell fate decision by schizophrenia-associated AS3MTd2d3 isoform during corticogenesis

The neurodevelopmental theory of schizophrenia emphasizes early brain development in its etiology. Genome-wide association studies have linked schizophrenia to genetic variations of AS3MT (arsenite methyltransferase) gene, particularly the increased expression of AS3MTd2d3 isoform. To investigate the biological basis of this association with schizophrenia pathophysiology, we established a transgenic mouse model (AS3MTd2d3-Tg) ectopically expressing AS3MTd2d3 at the cortical neural stem cells. AS3MTd2d3-Tg mice exhibited enlarged ventricles and deficits in sensorimotor gating and sociability. Single-cell and single-nucleus RNA sequencing analyses of AS3MTd2d3-Tg brains revealed cell fate imbalances and altered excitatory neuron composition. AS3MTd2d3 localized to centrosome, disrupting mitotic spindle orientation and differentiation in developing neocortex and organoids, in part through NPM1 (Nucleophosmin 1). The structural analysis identified that hydrophobic residues exposed in AS3MTd2d3 are critical for its pathogenic function. Therefore, our findings may help to explain the early pathological features of schizophrenia.

Decoding the Nectin Interactome: Implications for Brain Development, Plasticity, and Neurological Disorders

The nectin family of cell adhesion molecules (CAMs) comprising nectins and nectin-like molecules has emerged as a key regulator of various pivotal neural processes, including neuronal development, migration, synapse formation, and plasticity. Nectins engage in homophilic and heterophilic interactions to mediate cell-cell adhesion, contributing to the establishment and maintenance of neural circuits. Their extracellular domains facilitate trans-synaptic interactions, while intracellular domains participate in signaling cascades influencing cytoskeletal dynamics and synaptic function. The exhibition of distinct localization patterns in neurons, astrocytes, and the blood-brain barrier underscores their diverse roles in the brain. The dysregulation of nectins has been implicated in several neurological disorders, such as neurodevelopmental disorders, depression, schizophrenia, and Alzheimer's disease. This review examines the structural and functional characteristics of nectins and their distribution and molecular mechanisms governing neural connectivity and cognition. It further discusses experimental studies unraveling nectin-mediated pathophysiology and potential therapeutic interventions targeting nectin-related pathways. Collectively, this comprehensive analysis highlights the significance of nectins in brain development, function, and disorders, paving the way for future research directions and clinical implications.

IFN-γ signaling links ventriculomegaly to choroid plexus and ependyma dysfunction following maternal immune activation

Maternal immune activation (MIA) is a principal environmental risk factor contributing to autism spectrum disorder (ASD) and can be causally linked to ASD symptoms. In our study, we found that MIA triggered by poly (I: C) injection caused ventriculomegaly in offspring due to the dysfunction of the choroid plexus (Chp) and ependyma. We subsequently identified a sustained enhancement of interferon-γ (IFN-γ) signaling in the brain and serum of MIA offspring. Further study revealed that increased IFN-γ signaling could disrupt the barrier function of Chp epithelial cells by activating macrophages, and suppress the differentiation of primary ependymal cells via the signal transducer and activator of transcription 1/3 signaling. The effects of MIA on the offspring were mitigated by administration of IFNGR-blocking antibody in pregnant dams, while systemic maternal administration of IFN-γ was sufficient to mimic the effect of MIA. Overall, our findings revealed that ventriculomegaly caused by IFN-γ signaling could be a critical factor in compromising fetal brain development in MIA-induced ASD and provide a mechanistic framework for the association between maternal inflammation and abnormal development of ventricles in the offspring.

Research priorities for non-invasive therapies to improve hydrocephalus outcomes

The Hydrocephalus Association organized two workshops with the support of the Rudi Schulte Research Institute and Cincinnati Children's Hospital Medical Center entitled "Developing Non-Invasive Hydrocephalus Therapies: Molecular and Cellular Targets", held September 27-29, 2023, in Dallas, TX, and "Developing Non-Invasive Hydrocephalus Therapies: Advancing Towards Clinical Trials", held April 12-13, 2024, in Cincinnati, OH. The goal of these workshops was to explore the frontiers of ongoing research for non-invasive therapies for the treatment of hydrocephalus across all etiologies and to improve patient outcomes at all stages of diagnosis and management. During the consensus-building discussions throughout the research workshops, basic, translational, and clinical scientists aimed to identify the next steps to develop novel treatments for hydrocephalus. This detailed report discusses the research priorities that emerged from these workshops to inspire researchers and guide studies towards better treatment for people living with hydrocephalus.

PTEN mutations impair CSF dynamics and cortical networks by dysregulating periventricular neural progenitors

Enlargement of the cerebrospinal fluid (CSF)-filled brain ventricles (ventriculomegaly) is a defining feature of congenital hydrocephalus (CH) and an under-recognized concomitant of autism. Here, we show that de novo mutations in the autism risk gene PTEN are among the most frequent monogenic causes of CH and primary ventriculomegaly. Mouse Pten-mutant ventriculomegaly results from aqueductal stenosis due to hyperproliferation of periventricular Nkx2.1+ neural progenitor cells (NPCs) and increased CSF production from hyperplastic choroid plexus. Pten-mutant ventriculomegalic cortices exhibit network dysfunction from increased activity of Nkx2.1+ NPC-derived inhibitory interneurons. Raptor deletion or postnatal everolimus treatment corrects ventriculomegaly, rescues cortical deficits and increases survival by antagonizing mTORC1-dependent Nkx2.1+ NPC pathology. Thus, PTEN mutations concurrently alter CSF dynamics and cortical networks by dysregulating Nkx2.1+ NPCs. These results implicate a nonsurgical treatment for CH, demonstrate a genetic association of ventriculomegaly and ASD, and help explain neurodevelopmental phenotypes refractory to CSF shunting in select individuals with CH.

Multimodal insights into adult neurogenesis: An integrative review of multi-omics approaches

Adult neural stem cells divide to produce neurons that migrate to preexisting neuronal circuits in a process named adult neurogenesis. Adult neurogenesis is one of the most exciting areas of current neuroscience, and it may be involved in a range of brain functions, including cognition, learning, memory, and social and behavior changes. While there is a growing number of multi-omics studies on adult neurogenesis, generalized analyses from a multi-omics perspective are lacking. In this review, we summarize studies related to genomics, metabolomics, proteomics, epigenomics, transcriptomics, and microbiomics of adult neurogenesis, and then discuss their future research priorities and potential neighborhoods. This will provide theoretical guidance and new directions for future research on adult neurogenesis.

Neurodevelopmental Implications Underpinning Hereditary Spastic Paraplegia

BACKGROUND

Hereditary spastic paraplegia (HSP) is a group of rare genetic neurodegenerative disorders characterized by corticospinal tract abnormalities. But frequently, abnormalities of proteins implicated in HSP have been identified in brain disorders of childhood, raising the possibility that early brain developmental mechanism underlying HSP.

RESULTS AND CONCLUSIONS

Here we summarized the clinical features of 89 HSP subtypes and found most have onset of symptoms earliest reported in infancy or early childhood. Importantly, HSP patients showed early brain developmental related phenotypes such as microcephaly, ventricular enlargement, and corpus callosum dysplasia. In addition, the expression trajectories analysis showed HSP genes were diffusely expressed across all human prenatal cortical regions and most genes enriched from post-conception weeks 8-24, periods characterized by neuro progenitor proliferation and neurogenesis. Furthermore, studies utilizing patient derived induced pluripotent stem cells (iPSCs)/organoids and mouse models have suggested that most HSP proteins play either direct or indirect roles in the development of the central nervous system. Therefore, HSP possesses a neurodevelopmental aspect and is not merely a degenerative disease, which may aid in better understanding the pathogenesis of this disease.

Genetic and molecular mechanisms of hydrocephalus

Hydrocephalus is a neurological condition caused by aberrant circulation and/or obstructed cerebrospinal fluid (CSF) flow after cerebral ventricle abnormal dilatation. In the past 50 years, the diagnosis and treatment of hydrocephalus have remained understudied and underreported, and little progress has been made with respect to prevention or treatment. Further research on the pathogenesis of hydrocephalus is essential for developing new diagnostic, preventive, and therapeutic strategies. Various genetic and molecular abnormalities contribute to the mechanisms of hydrocephalus, including gene deletions or mutations, the activation of cellular inflammatory signaling pathways, alterations in water channel proteins, and disruptions in iron metabolism. Several studies have demonstrated that modulating the expression of key proteins, including TGF-β, VEGF, Wnt, AQP, NF-κB, and NKCC, can significantly influence the onset and progression of hydrocephalus. This review summarizes and discusses key mechanisms that may be involved in the pathogenesis of hydrocephalus at both the genetic and molecular levels. While obstructive hydrocephalus can often be addressed by removing the obstruction, most cases require treatment strategies that involve merely slowing disease progression by correcting CSF circulation patterns. There have been few new research breakthroughs in the prevention and treatment of hydrocephalus.

TRIM71 mutations cause a neurodevelopmental syndrome featuring ventriculomegaly and hydrocephalus

Congenital hydrocephalus, characterized by cerebral ventriculomegaly, is one of the most common reasons for paediatric brain surgery. Recent studies have implicated lin-41 (lineage variant 41)/TRIM71 (tripartite motif 71) as a candidate congenital hydrocephalus risk gene; however, TRIM71 variants have not been systematically examined in a large patient cohort or conclusively linked with an OMIM syndrome. Through cross-sectional analysis of the largest assembled cohort of patients with cerebral ventriculomegaly, including neurosurgically-treated congenital hydrocephalus (totalling 2697 parent-proband trios and 8091 total exomes), we identified 13 protein-altering de novo variants (DNVs) in TRIM71 in unrelated children exhibiting variable ventriculomegaly, congenital hydrocephalus, developmental delay, dysmorphic features and other structural brain defects, including corpus callosum dysgenesis and white matter hypoplasia. Eight unrelated patients were found to harbour arginine variants, including two recurrent missense DNVs, at homologous positions in RPXGV motifs of different NHL domains. Seven patients with rare, damaging, unphased or transmitted variants of uncertain significance were also identified. NHL-domain variants of TRIM71 exhibited impaired binding to the canonical TRIM71 target CDKN1A; other variants failed to direct the subcellular localization of TRIM71 to processing bodies. Single-cell transcriptomic analysis of human embryos revealed expression of TRIM71 in early first-trimester neural stem cells of the brain. These data show TRIM71 is essential for human brain morphogenesis and that TRIM71 mutations cause a novel neurodevelopmental syndrome that we term 'TRIM71-associated developmental disorders (TADD)', featuring variable ventriculomegaly, congenital hydrocephalus and other structural brain defects.

Biomechanical instability of the brain-CSF interface in hydrocephalus

Hydrocephalus, characterized by progressive expansion of the CSF-filled ventricles (ventriculomegaly), is the most common reason for brain surgery. 'Communicating' (i.e. non-obstructive) hydrocephalus is classically attributed to a primary derangement in CSF homeostasis, such as choroid plexus-dependent CSF hypersecretion, impaired cilia-mediated CSF flow currents, or decreased CSF reabsorption via the arachnoid granulations or other pathways. Emerging data suggest that abnormal biomechanical properties of the brain parenchyma are an under-appreciated driver of ventriculomegaly in multiple forms of communicating hydrocephalus across the lifespan. We discuss recent evidence from human and animal studies that suggests impaired neurodevelopment in congenital hydrocephalus, neurodegeneration in elderly normal pressure hydrocephalus and, in all age groups, inflammation-related neural injury in post-infectious and post-haemorrhagic hydrocephalus, can result in loss of stiffness and viscoelasticity of the brain parenchyma. Abnormal brain biomechanics create barrier alterations at the brain-CSF interface that pathologically facilitates secondary enlargement of the ventricles, even at normal or low intracranial pressures. This 'brain-centric' paradigm has implications for the diagnosis, treatment and study of hydrocephalus from womb to tomb.

Multiciliated ependymal cells: an update on biology and pathology in the adult brain

Mature multiciliated ependymal cells line the cerebral ventricles where they form a partial barrier between the cerebrospinal fluid (CSF) and brain parenchyma and regulate local CSF microcirculation through coordinated ciliary beating. Although the ependyma is a highly specialized brain interface with barrier, trophic, and perhaps even regenerative capacity, it remains a misfit in the canon of glial neurobiology. We provide an update to seminal reviews in the field by conducting a scoping review of the post-2010 mature multiciliated ependymal cell literature. We delineate how recent findings have either called into question or substantiated classical views of the ependymal cell. Beyond this synthesis, we document the basic methodologies and study characteristics used to describe multiciliated ependymal cells since 1980. Our review serves as a comprehensive resource for future investigations of mature multiciliated ependymal cells.

Ventricular-subventricular zone stem cell niche adaptations in a mouse model of post-infectious hydrocephalus

Congenital post-infectious hydrocephalus (PIH) is a condition characterized by enlargement of the ventricular system, consequently imposing a burden on the associated stem cell niche, the ventricular-subventricular zone (V-SVZ). To investigate how the V-SVZ adapts in PIH, we developed a mouse model of influenza virus-induced PIH based on direct intracerebroventricular injection of mouse-adapted influenza virus at two distinct time points: embryonic day 16 (E16), when stem cells line the ventricle, and postnatal day 4 (P4), when an ependymal monolayer covers the ventricle surface and stem cells retain only a thin ventricle-contacting process. Global hydrocephalus with associated regions of astrogliosis along the lateral ventricle was found in 82% of the mice infected at P4. Increased ependymogenesis was observed at gliotic borders and throughout areas exhibiting intact ependyma based on tracking of newly divided cells. Additionally, in areas of intact ependyma, stem cell numbers were reduced; however, we found no significant reduction in new neurons reaching the olfactory bulb following onset of ventriculomegaly. At P4, injection of only the non-infectious viral component neuraminidase resulted in limited, region-specific ventriculomegaly due to absence of cell-to-cell transmission. In contrast, at E16 intracerebroventricular injection of influenza virus resulted in death at birth due to hypoxia and multiorgan hemorrhage, suggesting an age-dependent advantage in neonates, while the viral component neuraminidase resulted in minimal, or no, ventriculomegaly. In summary, we tracked acute adaptations of the V-SVZ stem cell niche following onset of ventriculomegaly and describe developmental changes that help mitigate the severity of congenital PIH.

Regulation of brain fluid volumes and pressures: basic principles, intracranial hypertension, ventriculomegaly and hydrocephalus

The principles of cerebrospinal fluid (CSF) production, circulation and outflow and regulation of fluid volumes and pressures in the normal brain are summarised. Abnormalities in these aspects in intracranial hypertension, ventriculomegaly and hydrocephalus are discussed. The brain parenchyma has a cellular framework with interstitial fluid (ISF) in the intervening spaces. Framework stress and interstitial fluid pressure (ISFP) combined provide the total stress which, after allowing for gravity, normally equals intracerebral pressure (ICP) with gradients of total stress too small to measure. Fluid pressure may differ from ICP in the parenchyma and collapsed subarachnoid spaces when the parenchyma presses against the meninges. Fluid pressure gradients determine fluid movements. In adults, restricting CSF outflow from subarachnoid spaces produces intracranial hypertension which, when CSF volumes change very little, is called idiopathic intracranial hypertension (iIH). Raised ICP in iIH is accompanied by increased venous sinus pressure, though which is cause and which effect is unclear. In infants with growing skulls, restriction in outflow leads to increased head and CSF volumes. In adults, ventriculomegaly can arise due to cerebral atrophy or, in hydrocephalus, to obstructions to intracranial CSF flow. In non-communicating hydrocephalus, flow through or out of the ventricles is somehow obstructed, whereas in communicating hydrocephalus, the obstruction is somewhere between the cisterna magna and cranial sites of outflow. When normal outflow routes are obstructed, continued CSF production in the ventricles may be partially balanced by outflow through the parenchyma via an oedematous periventricular layer and perivascular spaces. In adults, secondary hydrocephalus with raised ICP results from obvious obstructions to flow. By contrast, with the more subtly obstructed flow seen in normal pressure hydrocephalus (NPH), fluid pressure must be reduced elsewhere, e.g. in some subarachnoid spaces. In idiopathic NPH, where ventriculomegaly is accompanied by gait disturbance, dementia and/or urinary incontinence, the functional deficits can sometimes be reversed by shunting or third ventriculostomy. Parenchymal shrinkage is irreversible in late stage hydrocephalus with cellular framework loss but may not occur in early stages, whether by exclusion of fluid or otherwise. Further studies that are needed to explain the development of hydrocephalus are outlined.

Dysregulation of FLVCR1a-dependent mitochondrial calcium handling in neural progenitors causes congenital hydrocephalus

Congenital hydrocephalus (CH), occurring in approximately 1/1,000 live births, represents an important clinical challenge due to the limited knowledge of underlying molecular mechanisms. The discovery of novel CH genes is thus essential to shed light on the intricate processes responsible for ventricular dilatation in CH. Here, we identify FLVCR1 (feline leukemia virus subgroup C receptor 1) as a gene responsible for a severe form of CH in humans and mice. Mechanistically, our data reveal that the full-length isoform encoded by the FLVCR1 gene, FLVCR1a, interacts with the IP3R3-VDAC complex located on mitochondria-associated membranes (MAMs) that controls mitochondrial calcium handling. Loss of Flvcr1a in mouse neural progenitor cells (NPCs) affects mitochondrial calcium levels and energy metabolism, leading to defective cortical neurogenesis and brain ventricle enlargement. These data point to defective NPCs calcium handling and metabolic activity as one of the pathogenetic mechanisms driving CH.

Pathogenic variants in autism gene KATNAL2 cause hydrocephalus and disrupt neuronal connectivity by impairing ciliary microtubule dynamics

Enlargement of the cerebrospinal fluid (CSF)-filled brain ventricles (cerebral ventriculomegaly), the cardinal feature of congenital hydrocephalus (CH), is increasingly recognized among patients with autism spectrum disorders (ASD). KATNAL2, a member of Katanin family microtubule-severing ATPases, is a known ASD risk gene, but its roles in human brain development remain unclear. Here, we show that nonsense truncation of Katnal2 (Katnal2Δ17) in mice results in classic ciliopathy phenotypes, including impaired spermatogenesis and cerebral ventriculomegaly. In both humans and mice, KATNAL2 is highly expressed in ciliated radial glia of the fetal ventricular-subventricular zone as well as in their postnatal ependymal and neuronal progeny. The ventriculomegaly observed in Katnal2Δ17 mice is associated with disrupted primary cilia and ependymal planar cell polarity that results in impaired cilia-generated CSF flow. Further, prefrontal pyramidal neurons in ventriculomegalic Katnal2Δ17 mice exhibit decreased excitatory drive and reduced high-frequency firing. Consistent with these findings in mice, we identified rare, damaging heterozygous germline variants in KATNAL2 in five unrelated patients with neurosurgically treated CH and comorbid ASD or other neurodevelopmental disorders. Mice engineered with the orthologous ASD-associated KATNAL2 F244L missense variant recapitulated the ventriculomegaly found in human patients. Together, these data suggest KATNAL2 pathogenic variants alter intraventricular CSF homeostasis and parenchymal neuronal connectivity by disrupting microtubule dynamics in fetal radial glia and their postnatal ependymal and neuronal descendants. The results identify a molecular mechanism underlying the development of ventriculomegaly in a genetic subset of patients with ASD and may explain persistence of neurodevelopmental phenotypes in some patients with CH despite neurosurgical CSF shunting.

Pathogenic variants associated with speech/cognitive delay and seizures affect genes with expression biases in excitatory neurons and microglia in developing human cortex

Background & Objective

Congenital brain malformations and neurodevelopmental disorders (NDDs) are common pediatric neurological disorders and result in chronic disability. With the expansion of genetic testing, new etiologies for NDDs are continually uncovered, with as many as one third attributable to single-gene pathogenic variants. While our ability to identify pathogenic variants has continually improved, we have little understanding of the underlying cellular pathophysiology in the nervous system that results from these variants. We therefore integrated phenotypic information from subjects with monogenic diagnoses with two large, single-nucleus RNA-sequencing (snRNAseq) datasets from human cortex across developmental stages in order to investigate cell-specific biases in gene expression associated with distinct neurodevelopmental phenotypes.

Methods

Phenotypic data was gathered from 1) a single-institution cohort of 84 neonates with pathogenic single-gene variants referred to Duke Pediatric Genetics, and 2) a cohort of 4,238 patients with neurodevelopmental disorders and pathogenic single-gene variants enrolled in the Deciphering Developmental Disorders (DDD) study. Pathogenic variants were grouped into genesets by neurodevelopmental phenotype and geneset expression across cortical cell subtypes was compared within snRNAseq datasets from 86 human cortex samples spanning the 2nd trimester of gestation to adulthood.

Results

We find that pathogenic variants associated with speech/cognitive delay or seizures involve genes that are more highly expressed in cortical excitatory neurons than variants in genes not associated with these phenotypes (Speech/cognitive: p=2.25×10-7; Seizures: p=7.97×10-12). A separate set of primarily rare variants associated with speech/cognitive delay or seizures, distinct from those with excitatory neuron expression biases, demonstrated expression biases in microglia. We also found that variants associated with speech/cognitive delay and an excitatory neuron expression bias could be further parsed by the presence or absence of comorbid seizures. Variants associated with speech/cognitive delay without seizures tended to involve calcium regulatory pathways and showed greater expression in extratelencephalic neurons, while those associated with speech/cognitive delay with seizures tended to involve synaptic regulatory machinery and an intratelencephalic neuron expression bias (ANOVA by geneset p<2×10-16).

Conclusions

By combining extensive phenotype datasets from subjects with neurodevelopmental disorders with massive human cortical snRNAseq datasets across developmental stages, we identified cell-specific expression biases for genes in which pathogenic variants are associated with speech/cognitive delay and seizures. The involvement of genes with enriched expression in excitatory neurons or microglia highlights the unique role both cell types play in proper sculpting of the developing brain. Moreover, this information begins to shed light on distinct cortical cell types that are more likely to be impacted by pathogenic variants and that may mediate the symptomatology of resulting neurodevelopmental disorders.

The subcommissural organ regulates brain development via secreted peptides

The subcommissural organ (SCO) is a gland located at the entrance of the aqueduct of Sylvius in the brain. It exists in species as distantly related as amphioxus and humans, but its function is largely unknown. Here, to explore its function, we compared transcriptomes of SCO and non-SCO brain regions and found three genes, Sspo, Car3 and Spdef, that are highly expressed in the SCO. Mouse strains expressing Cre recombinase from endogenous promoter/enhancer elements of these genes were used to genetically ablate SCO cells during embryonic development, resulting in severe hydrocephalus and defects in neuronal migration and development of neuronal axons and dendrites. Unbiased peptidomic analysis revealed enrichment of three SCO-derived peptides, namely, thymosin beta 4, thymosin beta 10 and NP24, and their reintroduction into SCO-ablated brain ventricles substantially rescued developmental defects. Together, these data identify a critical role for the SCO in brain development.

Paediatric hydrocephalus

Hydrocephalus is classically considered as a failure of cerebrospinal fluid (CSF) homeostasis that results in the active expansion of the cerebral ventricles. Infants with hydrocephalus can present with progressive increases in head circumference whereas older children often present with signs and symptoms of elevated intracranial pressure. Congenital hydrocephalus is present at or near birth and some cases have been linked to gene mutations that disrupt brain morphogenesis and alter the biomechanics of the CSF-brain interface. Acquired hydrocephalus can develop at any time after birth, is often caused by central nervous system infection or haemorrhage and has been associated with blockage of CSF pathways and inflammation-dependent dysregulation of CSF secretion and clearance. Treatments for hydrocephalus mainly include surgical CSF shunting or endoscopic third ventriculostomy with or without choroid plexus cauterization. In utero treatment of fetal hydrocephalus is possible via surgical closure of associated neural tube defects. Long-term outcomes for children with hydrocephalus vary widely and depend on intrinsic (genetic) and extrinsic factors. Advances in genomics, brain imaging and other technologies are beginning to refine the definition of hydrocephalus, increase precision of prognostication and identify nonsurgical treatment strategies.

A novel SMARCC1 BAFopathy implicates neural progenitor epigenetic dysregulation in human hydrocephalus

Hydrocephalus, characterized by cerebral ventriculomegaly, is the most common disorder requiring brain surgery in children. Recent studies have implicated SMARCC1, a component of the BRG1-associated factor (BAF) chromatin remodelling complex, as a candidate congenital hydrocephalus gene. However, SMARCC1 variants have not been systematically examined in a large patient cohort or conclusively linked with a human syndrome. Moreover, congenital hydrocephalus-associated SMARCC1 variants have not been functionally validated or mechanistically studied in vivo. Here, we aimed to assess the prevalence of SMARCC1 variants in an expanded patient cohort, describe associated clinical and radiographic phenotypes, and assess the impact of Smarcc1 depletion in a novel Xenopus tropicalis model of congenital hydrocephalus. To do this, we performed a genetic association study using whole-exome sequencing from a cohort consisting of 2697 total ventriculomegalic trios, including patients with neurosurgically-treated congenital hydrocephalus, that total 8091 exomes collected over 7 years (2016-23). A comparison control cohort consisted of 1798 exomes from unaffected siblings of patients with autism spectrum disorder and their unaffected parents were sourced from the Simons Simplex Collection. Enrichment and impact on protein structure were assessed in identified variants. Effects on the human fetal brain transcriptome were examined with RNA-sequencing and Smarcc1 knockdowns were generated in Xenopus and studied using optical coherence tomography imaging, in situ hybridization and immunofluorescence. SMARCC1 surpassed genome-wide significance thresholds, yielding six rare, protein-altering de novo variants localized to highly conserved residues in key functional domains. Patients exhibited hydrocephalus with aqueductal stenosis; corpus callosum abnormalities, developmental delay, and cardiac defects were also common. Xenopus knockdowns recapitulated both aqueductal stenosis and cardiac defects and were rescued by wild-type but not patient-specific variant SMARCC1. Hydrocephalic SMARCC1-variant human fetal brain and Smarcc1-variant Xenopus brain exhibited a similarly altered expression of key genes linked to midgestational neurogenesis, including the transcription factors NEUROD2 and MAB21L2. These results suggest de novo variants in SMARCC1 cause a novel human BAFopathy we term 'SMARCC1-associated developmental dysgenesis syndrome', characterized by variable presence of cerebral ventriculomegaly, aqueductal stenosis, developmental delay and a variety of structural brain or cardiac defects. These data underscore the importance of SMARCC1 and the BAF chromatin remodelling complex for human brain morphogenesis and provide evidence for a 'neural stem cell' paradigm of congenital hydrocephalus pathogenesis. These results highlight utility of trio-based whole-exome sequencing for identifying pathogenic variants in sporadic congenital structural brain disorders and suggest whole-exome sequencing may be a valuable adjunct in clinical management of congenital hydrocephalus patients.

The subcommissural organ regulates brain development via secreted peptides

The subcommissural organ (SCO) is a gland located at the entrance of the aqueduct of Sylvius in the brain. It exists in species as distantly related as amphioxus and humans, but its function is largely unknown. To explore its function, we compared transcriptomes of SCO and non-SCO brain regions and found three genes, Sspo, Car3, and Spdef, that are highly expressed in the SCO. Mouse strains expressing Cre recombinase from endogenous promoter/enhancer elements of these genes were used to genetically ablate SCO cells during embryonic development, resulting in severe hydrocephalus and defects in neuronal migration and development of neuronal axons and dendrites. Unbiased peptidomic analysis revealed enrichment of three SCO-derived peptides, namely thymosin beta 4, thymosin beta 10, and NP24, and their reintroduction into SCO-ablated brain ventricles substantially rescued developmental defects. Together, these data identify a critical role for the SCO in brain development.

ESCRT-I protein UBAP1 controls ventricular expansion and cortical neurogenesis via modulating adherens junctions of radial glial cells

Intricate cerebral cortex formation is orchestrated by the precise behavior and division dynamics of radial glial cells (RGCs). Endocytosis functions in the recycling and remodeling of adherens junctions (AJs) in response to changes in RGC activity and function. Here, we show that conditional disruption of ubiquitin-associated protein 1 (UBAP1), a component of endosomal sorting complex required for transport (ESCRT), causes severe brain dysplasia and prenatal ventriculomegaly. UBAP1 depletion disrupts the AJs and polarity of RGCs, leading to failure of apically directed interkinetic nuclear migration. Accordingly, UBAP1 knockout or knockdown results in reduced proliferation and precocious differentiation of neural progenitor cells. Mechanistically, UBAP1 regulates the expression and surface localization of cell adhesion molecules, and β-catenin over-expression significantly rescues the phenotypes of Ubap1 knockdown in vivo. Our study reveals a critical physiological role of the ESCRT machinery in cortical neurogenesis by regulating AJs of RGCs.

The homozygous pathogenic variant of the POMGNT1 gene identified using whole-exome sequencing in Iranian family with congenital hydrocephalus

Background

Hydrocephalus is one of the most common pathophysiological disabilities with a high mortality rate, which occurs both congenitally and acquired. It is estimated that genetic components are the etiology for up to 40% of hydrocephalus cases; however, causal mutations identified until now could only explain approximately 20% of congenital hydrocephalus (CH) patients, and most potential hydrocephalus-associated genes have yet to be determined. This study sought to find causal variations in a consanguineous family with four affected children diagnosed with hydrocephalus.

Material and methods

In this study, we evaluated twenty-five members of an extended family consisting of a nuclear family with four affected children resulting from a consanguineous couple and eighteen of their relatives, including one hydrocephalus case. The mother of this family was experiencing her 15th week of pregnancy, and cytogenetic evaluation was performed using amniocentesis to identify fetal chromosomal abnormalities. We conducted whole-exome sequencing (WES) on the genomic DNA of the proband to detect the CH-causing variants, followed by confirmation and segregation analysis of the detected variant in the proband, fetus, and family members through Sanger sequencing.

Results

Following the bioinformatic analysis and data filtering, we found a homozygous variant [NM_001243766.2:c.74G>A:p.W25X] within the protein O-mannose beta-1,2-N-acetylglucosaminyltransferase 1 (POMGNT1) gene confirmed by Sanger sequencing in the proband and segregated with the hydrocephalus in the family. The variant was described as pathogenic and regarded as a nonsense-mediated mRNA decay (NMD) due to the premature stop codon, which results in a truncated protein.

Conclusion

The results of the current study broadened the mutational gene spectrum of CH and our knowledge of the hydrocephalus etiology by introducing a novel homozygous variant within the POMGNT1 gene, which had never been previously reported solitary in these patients.

The genetic basis of hydrocephalus: genes, pathways, mechanisms, and global impact

Hydrocephalus (HC) is a heterogenous disease characterized by alterations in cerebrospinal fluid (CSF) dynamics that may cause increased intracranial pressure. HC is a component of a wide array of genetic syndromes as well as a secondary consequence of brain injury (intraventricular hemorrhage (IVH), infection, etc.) that can present across the age spectrum, highlighting the phenotypic heterogeneity of the disease. Surgical treatments include ventricular shunting and endoscopic third ventriculostomy with or without choroid plexus cauterization, both of which are prone to failure, and no effective pharmacologic treatments for HC have been developed. Thus, there is an urgent need to understand the genetic architecture and molecular pathogenesis of HC. Without this knowledge, the development of preventive, diagnostic, and therapeutic measures is impeded. However, the genetics of HC is extraordinarily complex, based on studies of varying size, scope, and rigor. This review serves to provide a comprehensive overview of genes, pathways, mechanisms, and global impact of genetics contributing to all etiologies of HC in humans.

Outer membrane vesicles and the outer membrane protein OmpU govern Vibrio cholerae biofilm matrix assembly

Biofilms are matrix-encased microbial communities that increase the environmental fitness and infectivity of many human pathogens including Vibrio cholerae. Biofilm matrix assembly is essential for biofilm formation and function. Known components of the V. cholerae biofilm matrix are the polysaccharide Vibrio polysaccharide (VPS), matrix proteins RbmA, RbmC, Bap1, and extracellular DNA, but the majority of the protein composition is uncharacterized. This study comprehensively analyzed the biofilm matrix proteome and revealed the presence of outer membrane proteins (OMPs). Outer membrane vesicles (OMVs) were also present in the V. cholerae biofilm matrix and were associated with OMPs and many biofilm matrix proteins suggesting that they participate in biofilm matrix assembly. Consistent with this, OMVs had the capability to alter biofilm structural properties depending on their composition. OmpU was the most prevalent OMP in the matrix, and its absence altered biofilm architecture by increasing VPS production. Single-cell force spectroscopy revealed that proteins critical for biofilm formation, OmpU, the matrix proteins RbmA, RbmC, Bap1, and VPS contribute to cell-surface adhesion forces at differing efficiency, with VPS showing the highest efficiency whereas Bap1 showing the lowest efficiency. Our findings provide new insights into the molecular mechanisms underlying biofilm matrix assembly in V. cholerae, which may provide new opportunities to develop inhibitors that specifically alter biofilm matrix properties and, thus, affect either the environmental survival or pathogenesis of V. cholerae.IMPORTANCECholera remains a major public health concern. Vibrio cholerae, the causative agent of cholera, forms biofilms, which are critical for its transmission, infectivity, and environmental persistence. While we know that the V. cholerae biofilm matrix contains exopolysaccharide, matrix proteins, and extracellular DNA, we do not have a comprehensive understanding of the majority of biofilm matrix components. Here, we discover outer membrane vesicles (OMVs) within the biofilm matrix of V. cholerae. Proteomic analysis of the matrix and matrix-associated OMVs showed that OMVs carry key matrix proteins and Vibrio polysaccharide (VPS) to help build biofilms. We also characterize the role of the highly abundant outer membrane protein OmpU in biofilm formation and show that it impacts biofilm architecture in a VPS-dependent manner. Understanding V. cholerae biofilm formation is important for developing a better prevention and treatment strategy framework.

Molecular mechanism governing RNA-binding property of mammalian TRIM71 protein

TRIM71 is an RNA-binding protein with ubiquitin ligase activity. Numerous functions of mammalian TRIM71, including cell cycle regulation, embryonic stem cell (ESC) self-renewal, and reprogramming of pluripotent stem cells, are related to its RNA-binding property. We previously reported that a long noncoding RNA (lncRNA) Trincr1 interacts with mouse TRIM71 (mTRIM71) to repress FGF/ERK pathway in mouse ESCs (mESCs). Herein, we identify an RNA motif specifically recognized by mTRIM71 from Trincr1 RNA, and solve the crystal structure of the NHL domain of mTRIM71 complexed with the RNA motif. Similar to the zebrafish TRIM71, mTRIM71 binds to a stem-loop structured RNA fragment of Trincr1, and an adenosine base at the loop region is crucial for the mTRIM71 interaction. We map similar hairpin RNAs preferably bound by TRIM71 in the mRNA UTRs of the cell-cycle related genes regulated by TRIM71. Furthermore, we identify key residues of mTRIM71, conserved among mammalian TRIM71 proteins, required for the RNA-binding property. Single-site mutations of these residues significantly impair the binding of TRIM71 to hairpin RNAs in vitro and to mRNAs of Cdkn1a/p21 and Rbl2/p130 in mESCs. Furthermore, congenital hydrocephalus (CH) specific mutation of mTRIM71 impair its binding to the RNA targets as well. These results reveal molecular mechanism behind the recognition of RNA by mammalian TRIM71 and provide insights into TRIM71 related diseases.

The "microcephalic hydrocephalus" paradox as a paradigm of altered neural stem cell biology

Characterized by enlarged brain ventricles, hydrocephalus is a common neurological disorder classically attributed to a primary defect in cerebrospinal fluid (CSF) homeostasis. Microcephaly ("small head") and hydrocephalus are typically viewed as two mutually exclusive phenomenon, since hydrocephalus is thought of as a fluid "plumbing" disorder leading to CSF accumulation, ventricular dilatation, and resultant macrocephaly. However, some cases of hydrocephalus can be associated with microcephaly. Recent work in the genomics of congenital hydrocephalus (CH) and an improved understanding of the tropism of certain viruses such as Zika and cytomegalovirus are beginning to shed light into the paradox "microcephalic hydrocephalus" by defining prenatal neural stem cells (NSC) as the spatiotemporal "scene of the crime." In some forms of CH and viral brain infections, impaired fetal NSC proliferation leads to decreased neurogenesis, cortical hypoplasia and impaired biomechanical interactions at the CSF-brain interface that collectively engender ventriculomegaly despite an overall and often striking decrease in head circumference. The coexistence of microcephaly and hydrocephalus suggests that these two phenotypes may overlap more than previously appreciated. Continued study of both conditions may be unexpectedly fertile ground for providing new insights into human NSC biology and our understanding of neurodevelopmental disorders.

Genetic architectures of cerebral ventricles and their overlap with neuropsychiatric traits

The cerebral ventricles are recognized as windows into brain development and disease, yet their genetic architectures, underlying neural mechanisms and utility in maintaining brain health remain elusive. Here we aggregated genetic and neuroimaging data from 61,974 participants (age range, 9 to 98 years) in five cohorts to elucidate the genetic basis of ventricular morphology and examined their overlap with neuropsychiatric traits. Genome-wide association analysis in a discovery sample of 31,880 individuals identified 62 unique loci and 785 candidate genes associated with ventricular morphology. We replicated over 80% of loci in a well-matched cohort of lateral ventricular volume. Gene set analysis revealed enrichment of ventricular-trait-associated genes in biological processes and disease pathogenesis during both early brain development and degeneration. We explored the age-dependent genetic associations in cohorts of different age groups to investigate the possible roles of ventricular-trait-associated loci in neurodevelopmental and neurodegenerative processes. We describe the genetic overlap between ventricular and neuropsychiatric traits through comprehensive integrative approaches under correlative and causal assumptions. We propose the volume of the inferior lateral ventricles as a heritable endophenotype to predict the risk of Alzheimer's disease, which might be a consequence of prodromal Alzheimer's disease. Our study provides an advance in understanding the genetics of the cerebral ventricles and demonstrates the potential utility of ventricular measurements in tracking brain disorders and maintaining brain health across the lifespan.

Concurrent impact of de novo mutations on cranial and cortical development in nonsyndromic craniosynostosis

OBJECTIVE

Nonsyndromic craniosynostosis (nsCS), characterized by premature cranial suture fusion, is considered a primary skull disorder in which impact on neurodevelopment, if present, results from the mechanical hindrance of brain growth. Despite surgical repair of the cranial defect, neurocognitive deficits persist in nearly half of affected children. Therefore, the authors performed a functional genomics analysis of nsCS to determine when, where, and in what cell types nsCS-associated genes converge during development.

METHODS

The authors integrated whole-exome sequencing data from 291 nsCS proband-parent trios with 29,803 single-cell transcriptomes of the prenatal and postnatal neurocranial complex to inform when, where, and in what cell types nsCS-mutated genes might exert their pathophysiological effects.

RESULTS

The authors found that nsCS-mutated genes converged in cranial osteoprogenitors and pial fibroblasts and their transcriptional networks that regulate both skull ossification and cerebral neurogenesis. Nonsyndromic CS-mutated genes also converged in inhibitory neurons and gene coexpression modules that overlapped with autism and other developmental disorders. Ligand-receptor cell-cell communication analysis uncovered crosstalk between suture osteoblasts and neurons via the nsCS-associated BMP, FGF, and noncanonical WNT signaling pathways.

CONCLUSIONS

These data implicate a concurrent impact of nsCS-associated de novo mutations on cranial morphogenesis and cortical development via cell- and non-cell-autonomous mechanisms in a developmental nexus of fetal osteoblasts, pial fibroblasts, and neurons. These results suggest that neurodevelopmental outcomes in nsCS patients may be driven more by mutational status than surgical technique.

The molecular genetic landscape of human brain size variation

Human brain size changes dynamically through early development, peaks in adolescence, and varies up to 2-fold among adults. However, the molecular genetic underpinnings of interindividual variation in brain size remain unknown. Here, we leveraged postmortem brain RNA sequencing and measurements of brain weight (BW) in 2,531 individuals across three independent datasets to identify 928 genome-wide significant associations with BW. Genes associated with higher or lower BW showed distinct neurodevelopmental trajectories and spatial patterns that mapped onto functional and cellular axes of brain organization. Expression of BW genes was predictive of interspecies differences in brain size, and bioinformatic annotation revealed enrichment for neurogenesis and cell-cell communication. Genome-wide, transcriptome-wide, and phenome-wide association analyses linked BW gene sets to neuroimaging measurements of brain size and brain-related clinical traits. Cumulatively, these results represent a major step toward delineating the molecular pathways underlying human brain size variation in health and disease.

WT, Arnold SE, Frosch MP, Duy PQ, Kahle KT. Cases of familial idiopathic normal pressure hydrocephalus implicate genetic factors in disease pathogenesis

Idiopathic normal pressure hydrocephalus is a disorder of unknown pathophysiology whose diagnosis is paradoxically made by a positive response to its proposed treatment with cerebrospinal fluid diversion. There are currently no idiopathic normal pressure hydrocephalus disease genes or biomarkers. A systematic analysis of familial idiopathic normal pressure hydrocephalus could aid in clinical diagnosis, prognosis, and treatment stratification, and elucidate disease patho-etiology. In this 2-part analysis, we review literature-based evidence for inheritance of idiopathic normal pressure hydrocephalus in 22 pedigrees, and then present a novel case series of 8 familial idiopathic normal pressure hydrocephalus patients. For the case series, demographics, familial history, pre- and post-operative symptoms, and cortical pathology were collected. All novel familial idiopathic normal pressure hydrocephalus patients exhibited improvement following shunt treatment and absence of neurodegenerative cortical pathology (amyloid-beta and hyperphosphorylated tau), in contrast to many sporadic cases of idiopathic normal pressure hydrocephalus with variable clinical responses. Analysis of the 30 total familial idiopathic normal pressure hydrocephalus cases reported herein is highly suggestive of an autosomal dominant mechanism of inheritance. This largest-ever presentation of multiply affected idiopathic normal pressure hydrocephalus pedigrees provides strong evidence for Mendelian inheritance and autosomal dominant transmission of an idiopathic normal pressure hydrocephalus trait in a subset of patients that positively respond to shunting and lack neurodegenerative pathology. Genomic investigation of these families may identify the first bona fide idiopathic normal pressure hydrocephalus disease gene.

Mutation of key signaling regulators of cerebrovascular development in vein of Galen malformations

To elucidate the pathogenesis of vein of Galen malformations (VOGMs), the most common and most severe of congenital brain arteriovenous malformations, we performed an integrated analysis of 310 VOGM proband-family exomes and 336,326 human cerebrovasculature single-cell transcriptomes. We found the Ras suppressor p120 RasGAP (RASA1) harbored a genome-wide significant burden of loss-of-function de novo variants (2042.5-fold, p = 4.79 x 10-7). Rare, damaging transmitted variants were enriched in Ephrin receptor-B4 (EPHB4) (17.5-fold, p = 1.22 x 10-5), which cooperates with p120 RasGAP to regulate vascular development. Additional probands had damaging variants in ACVRL1, NOTCH1, ITGB1, and PTPN11. ACVRL1 variants were also identified in a multi-generational VOGM pedigree. Integrative genomic analysis defined developing endothelial cells as a likely spatio-temporal locus of VOGM pathophysiology. Mice expressing a VOGM-specific EPHB4 kinase-domain missense variant (Phe867Leu) exhibited disrupted developmental angiogenesis and impaired hierarchical development of arterial-capillary-venous networks, but only in the presence of a "second-hit" allele. These results illuminate human arterio-venous development and VOGM pathobiology and have implications for patients and their families.

Heterozygous FOXJ1 Mutations Cause Incomplete Ependymal Cell Differentiation and Communicating Hydrocephalus

Heterozygous mutations affecting FOXJ1, a transcription factor governing multiciliated cell development, have been associated with obstructive hydrocephalus in humans. However, factors that disrupt multiciliated ependymal cell function often cause communicating hydrocephalus, raising questions about whether FOXJ1 mutations cause hydrocephalus primarily by blocking cerebrospinal fluid (CSF) flow or by different mechanisms. Here, we show that heterozygous FOXJ1 mutations are also associated with communicating hydrocephalus in humans and cause communicating hydrocephalus in mice. Disruption of one Foxj1 allele in mice leads to incomplete ependymal cell differentiation and communicating hydrocephalus. Mature ependymal cell number and motile cilia number are decreased, and 12% of motile cilia display abnormal axonemes. We observed decreased microtubule attachment to basal bodies, random localization and orientation of basal body patches, loss of planar cell polarity, and a disruption of unidirectional CSF flow. Thus, heterozygous FOXJ1 mutations impair ventricular multiciliated cell differentiation, thereby causing communicating hydrocephalus. CSF flow obstruction may develop secondarily in some patients harboring FOXJ1 mutations. Heterozygous FOXJ1 mutations impair motile cilia structure and basal body alignment, thereby disrupting CSF flow dynamics and causing communicating hydrocephalus.

Atypical fetal brain development in fetuses with non-syndromic isolated musculoskeletal birth defects (niMSBDs)

Non-syndromic, isolated musculoskeletal birth defects (niMSBDs) are among the leading causes of pediatric hospitalization. However, little is known about brain development in niMSBDs. Our study aimed to characterize prenatal brain development in fetuses with niMSBDs and identify altered brain regions compared to controls. We retrospectively analyzed in vivo structural T2-weighted MRIs of 99 fetuses (48 controls and 51 niMSBDs cases). For each group (19-31 and >31 gestational weeks (GW)), we conducted repeated-measures regression analysis with relative regional volume (% brain hemisphere) as a dependent variable (adjusted for age, side, and interactions). Between 19 and 31GW, fetuses with niMSBDs had a significantly (P < 0.001) smaller relative volume of the intermediate zone (-22.9 ± 3.2%) and cerebellum (-16.1 ± 3.5%,) and a larger relative volume of proliferative zones (38.3 ± 7.2%), the ganglionic eminence (34.8 ± 7.3%), and the ventricles (35.8 ± 8.0%). Between 32 and 37 GW, compared to the controls, niMSBDs showed significantly smaller volumes of central regions (-9.1 ± 2.1%) and larger volumes of the cortical plate. Our results suggest there is altered brain development in fetuses with niMSBDs compared to controls (13.1 ± 4.2%). Further basic and translational neuroscience research is needed to better visualize these differences and to characterize the altered development in fetuses with specific niMSBDs.

TRIM71 reactivation enhances the mitotic and hair cell-forming potential of cochlear supporting cells

Cochlear hair cell loss is a leading cause of deafness in humans. Neighboring supporting cells have some capacity to regenerate hair cells. However, their regenerative potential sharply declines as supporting cells undergo maturation (postnatal day 5 in mice). We recently reported that reactivation of the RNA-binding protein LIN28B restores the hair cell-regenerative potential of P5 cochlear supporting cells. Here, we identify the LIN28B target Trim71 as a novel and equally potent enhancer of supporting cell plasticity. TRIM71 is a critical regulator of stem cell behavior and cell reprogramming; however, its role in cell regeneration is poorly understood. Employing an organoid-based assay, we show that TRIM71 re-expression increases the mitotic and hair cell-forming potential of P5 cochlear supporting cells by facilitating their de-differentiation into progenitor-like cells. Our mechanistic work indicates that TRIM71's RNA-binding activity is essential for such ability, and our transcriptomic analysis identifies gene modules that are linked to TRIM71 and LIN28B-mediated supporting cell reprogramming. Furthermore, our study uncovers that the TRIM71-LIN28B target Hmga2 is essential for supporting cell self-renewal and hair cell formation.

"Floppy brain" in congenital hydrocephalus

Hydrocephalus is classically considered to be a disorder of altered cerebrospinal fluid (CSF) circulation, leading to the dilation of cerebral ventricles. Here, we report a clinical case of a patient who presented with fetal-onset hydrocephalus with diffusely reduced cortical and white matter volumes resulting from a genetic mutation in L1CAM, a well-known hydrocephalus disease gene involved in neuronal cell adhesion and axon development. After CSF was drained from the ventricle intraoperatively, the patient's cortical mantle collapsed and exhibited a "floppy" appearance on neuroimaging, suggesting an inability of the hydrocephalic brain to maintain its structural integrity. The case provides clinical support for altered brain biomechanical properties in human hydrocephalus and adds to the emerging hypothesis that altered brain development with secondary impact on brain structural stability may contribute to ventricular enlargement in some subsets of hydrocephalus.

Continuous positive airway pressure increases CSF flow and glymphatic transport

Respiration can positively influence cerebrospinal fluid (CSF) flow in the brain, yet its effects on central nervous system (CNS) fluid homeostasis, including waste clearance function via glymphatic and meningeal lymphatic systems, remain unclear. Here, we investigated the effect of supporting respiratory function via continuous positive airway pressure (CPAP) on glymphatic-lymphatic function in spontaneously breathing anesthetized rodents. To do this, we used a systems approach combining engineering, MRI, computational fluid dynamics analysis, and physiological testing. We first designed a nasal CPAP device for use in the rat and demonstrated that it functioned similarly to clinical devices, as evidenced by its ability to open the upper airway, augment end-expiratory lung volume, and improve arterial oxygenation. We further showed that CPAP increased CSF flow speed at the skull base and augmented glymphatic transport regionally. The CPAP-induced augmented CSF flow speed was associated with an increase in intracranial pressure (ICP), including the ICP waveform pulse amplitude. We suggest that the augmented pulse amplitude with CPAP underlies the increase in CSF bulk flow and glymphatic transport. Our results provide insights into the functional crosstalk at the pulmonary-CSF interface and suggest that CPAP might have therapeutic benefit for sustaining glymphatic-lymphatic function.

Convergence of multiple RNA-silencing pathways on GW182/TNRC6

The RNA-binding protein TRIM71/LIN-41 is a phylogenetically conserved developmental regulator that functions in mammalian stem cell reprogramming, brain development, and cancer. TRIM71 recognizes target mRNAs through hairpin motifs and silences them through molecular mechanisms that await identification. Here, we uncover that TRIM71 represses its targets through RNA-supported interaction with TNRC6/GW182, a core component of the miRNA-induced silencing complex (miRISC). We demonstrate that AGO2, TRIM71, and UPF1 each recruit TNRC6 to specific sets of transcripts to silence them. As cellular TNRC6 levels are limiting, competition occurs among the silencing pathways, such that the loss of AGO proteins or of AGO binding to TNRC6 enhances the activities of the other pathways. We conclude that a miRNA-like silencing activity is shared among different mRNA silencing pathways and that the use of TNRC6 as a central hub provides a means to integrate their activities.

A year in review: brain barriers and brain fluids research in 2022

This aim of this editorial is to highlight progress made in brain barrier and brain fluid research in 2022. It covers studies on the blood-brain, blood-retina and blood-CSF barriers (choroid plexus and meninges), signaling within the neurovascular unit and elements of the brain fluid systems. It further discusses how brain barriers and brain fluid systems are impacted in CNS diseases, their role in disease progression and progress being made in treating such diseases.

Abnormal prenatal brain development in Chiari II malformation

Introduction

The Chiari II is a relatively common birth defect that is associated with open spinal abnormalities and is characterized by caudal migration of the posterior fossa contents through the foramen magnum. The pathophysiology of Chiari II is not entirely known, and the neurobiological substrate beyond posterior fossa findings remains unexplored. We aimed to identify brain regions altered in Chiari II fetuses between 17 and 26 GW.

Methods

We used in vivo structural T2-weighted MRIs of 31 fetuses (6 controls and 25 cases with Chiari II).

Results

The results of our study indicated altered development of diencephalon and proliferative zones (ventricular and subventricular zones) in fetuses with a Chiari II malformation compared to controls. Specifically, fetuses with Chiari II showed significantly smaller volumes of the diencephalon and significantly larger volumes of lateral ventricles and proliferative zones.

Discussion

We conclude that regional brain development should be taken into consideration when evaluating prenatal brain development in fetuses with Chiari II.

A neural stem cell paradigm of pediatric hydrocephalus

Pediatric hydrocephalus, the leading reason for brain surgery in children, is characterized by enlargement of the cerebral ventricles classically attributed to cerebrospinal fluid (CSF) overaccumulation. Neurosurgical shunting to reduce CSF volume is the default treatment that intends to reinstate normal CSF homeostasis, yet neurodevelopmental disability often persists in hydrocephalic children despite optimal surgical management. Here, we discuss recent human genetic and animal model studies that are shifting the view of pediatric hydrocephalus from an impaired fluid plumbing model to a new paradigm of dysregulated neural stem cell (NSC) fate. NSCs are neuroprogenitor cells that comprise the germinal neuroepithelium lining the prenatal brain ventricles. We propose that heterogenous defects in the development of these cells converge to disrupt cerebrocortical morphogenesis, leading to abnormal brain-CSF biomechanical interactions that facilitate passive pooling of CSF and secondary ventricular distention. A significant subset of pediatric hydrocephalus may thus in fact be due to a developmental brain malformation leading to secondary enlargement of the ventricles rather than a primary defect of CSF circulation. If hydrocephalus is indeed a neuroradiographic presentation of an inborn brain defect, it suggests the need to focus on optimizing neurodevelopment, rather than CSF diversion, as the primary treatment strategy for these children.

A mathematical framework for the dynamic interaction of pulsatile blood, brain, and cerebrospinal fluid

BACKGROUND

Shedding light on less-known aspects of intracranial fluid dynamics may be helpful to understand the hydrocephalus mechanism. The present study suggests a mathematical framework based on in vivo inputs to compare the dynamic interaction of pulsatile blood, brain, and cerebrospinal fluid (CSF) between the healthy subject and the hydrocephalus patient.

METHOD

The input data for the mathematical formulations was pulsatile blood velocity, which was measured using cine PC-MRI. Tube law was used to transfer the created deformation by blood pulsation in the vessel circumference to the brain domain. The pulsatile deformation of brain tissue with respect to time was calculated and considered to be inlet velocity in the CSF domain. The governing equations in all three domains were continuity, Navier-Stokes, and concentration. We used Darcy law with defined permeability and diffusivity values to define the material properties in the brain.

RESULTS

We validated the preciseness of the CSF velocity and pressure through the mathematical formulations with cine PC-MRI velocity, experimental ICP, and FSI simulated velocity and pressure. We used the analysis of dimensionless numbers including Reynolds, Womersley, Hartmann, and Peclet to evaluate the characteristics of the intracranial fluid flow. In the mid-systole phase of a cardiac cycle, CSF velocity had the maximum value and CSF pressure had the minimum value. The maximum and amplitude of CSF pressure, as well as CSF stroke volume, were calculated and compared between the healthy subject and the hydrocephalus patient.

CONCLUSION

The present in vivo-based mathematical framework has the potential to gain insight into the less-known points in the physiological function of intracranial fluid dynamics and the hydrocephalus mechanism.

Genetic dysregulation of an endothelial Ras signaling network in vein of Galen malformations

To elucidate the pathogenesis of vein of Galen malformations (VOGMs), the most common and severe congenital brain arteriovenous malformation, we performed an integrated analysis of 310 VOGM proband-family exomes and 336,326 human cerebrovasculature single-cell transcriptomes. We found the Ras suppressor p120 RasGAP ( RASA1 ) harbored a genome-wide significant burden of loss-of-function de novo variants (p=4.79×10 ^-7 ). Rare, damaging transmitted variants were enriched in Ephrin receptor-B4 ( EPHB4 ) (p=1.22×10 ^-5 ), which cooperates with p120 RasGAP to limit Ras activation. Other probands had pathogenic variants in ACVRL1 , NOTCH1 , ITGB1 , and PTPN11 . ACVRL1 variants were also identified in a multi-generational VOGM pedigree. Integrative genomics defined developing endothelial cells as a key spatio-temporal locus of VOGM pathophysiology. Mice expressing a VOGM-specific EPHB4 kinase-domain missense variant exhibited constitutive endothelial Ras/ERK/MAPK activation and impaired hierarchical development of angiogenesis-regulated arterial-capillary-venous networks, but only when carrying a "second-hit" allele. These results illuminate human arterio-venous development and VOGM pathobiology and have clinical implications.

A novel SMARCC1 -mutant BAFopathy implicates epigenetic dysregulation of neural progenitors in hydrocephalus

Importance

Hydrocephalus, characterized by cerebral ventriculomegaly, is the most common disorder requiring brain surgery. A few familial forms of congenital hydrocephalus (CH) have been identified, but the cause of most sporadic cases of CH remains elusive. Recent studies have implicated SMARCC1 , a component of the B RG1- a ssociated factor (BAF) chromatin remodeling complex, as a candidate CH gene. However, SMARCC1 variants have not been systematically examined in a large patient cohort or conclusively linked with a human syndrome. Moreover, CH-associated SMARCC1 variants have not been functionally validated or mechanistically studied in vivo .

Objectives

The aims of this study are to (i) assess the extent to which rare, damaging de novo mutations (DNMs) in SMARCC1 are associated with cerebral ventriculomegaly; (ii) describe the clinical and radiographic phenotypes of SMARCC1 -mutated patients; and (iii) assess the pathogenicity and mechanisms of CH-associated SMARCC1 mutations in vivo .

Design setting and participants

A genetic association study was conducted using whole-exome sequencing from a cohort consisting of 2,697 ventriculomegalic trios, including patients with neurosurgically-treated CH, totaling 8,091 exomes collected over 5 years (2016-2021). Data were analyzed in 2023. A comparison control cohort consisted of 1,798 exomes from unaffected siblings of patients with autism spectrum disorder and their unaffected parents sourced from the Simons simplex consortium.

Main outcomes and measures

Gene variants were identified and filtered using stringent, validated criteria. Enrichment tests assessed gene-level variant burden. In silico biophysical modeling estimated the likelihood and extent of the variant impact on protein structure. The effect of a CH-associated SMARCC1 mutation on the human fetal brain transcriptome was assessed by analyzing RNA-sequencing data. Smarcc1 knockdowns and a patient-specific Smarcc1 variant were tested in Xenopus and studied using optical coherence tomography imaging, in situ hybridization, and immunofluorescence microscopy.

Results

SMARCC1 surpassed genome-wide significance thresholds in DNM enrichment tests. Six rare protein-altering DNMs, including four loss-of-function mutations and one recurrent canonical splice site mutation (c.1571+1G>A) were detected in unrelated patients. DNMs localized to the highly conserved DNA-interacting SWIRM, Myb-DNA binding, Glu-rich, and Chromo domains of SMARCC1 . Patients exhibited developmental delay (DD), aqueductal stenosis, and other structural brain and heart defects. G0 and G1 Smarcc1 Xenopus mutants exhibited aqueductal stenosis and cardiac defects and were rescued by human wild-type SMARCC1 but not a patient-specific SMARCC1 mutant. Hydrocephalic SMARCC1 -mutant human fetal brain and Smarcc1 -mutant Xenopus brain exhibited a similarly altered expression of key genes linked to midgestational neurogenesis, including the transcription factors NEUROD2 and MAB21L2 .

Conclusions

SMARCC1 is a bona fide CH risk gene. DNMs in SMARCC1 cause a novel human BAFopathy we term " S MARCC1- a ssociated D evelopmental D ysgenesis S yndrome (SaDDS)", characterized by cerebral ventriculomegaly, aqueductal stenosis, DD, and a variety of structural brain or cardiac defects. These data underscore the importance of SMARCC1 and the BAF chromatin remodeling complex for human brain morphogenesis and provide evidence for a "neural stem cell" paradigm of human CH pathogenesis. These results highlight the utility of trio-based WES for identifying risk genes for congenital structural brain disorders and suggest WES may be a valuable adjunct in the clinical management of CH patients.

KEY POINTS

Question: What is the role of SMARCC1 , a core component of the B RG1- a ssociated factor (BAF) chromatin remodeling complex, in brain morphogenesis and congenital hydrocephalus (CH)? Findings: SMARCC1 harbored an exome-wide significant burden of rare, protein-damaging de novo mutations (DNMs) (p = 5.83 × 10 -9 ) in the largest ascertained cohort to date of patients with cerebral ventriculomegaly, including treated CH (2,697 parent-proband trios). SMARCC1 contained four loss-of-function DNMs and two identical canonical splice site DNMs in a total of six unrelated patients. Patients exhibited developmental delay, aqueductal stenosis, and other structural brain and cardiac defects. Xenopus Smarcc1 mutants recapitulated core human phenotypes and were rescued by the expression of human wild-type but not patient-mutant SMARCC1 . Hydrocephalic SMARCC1 -mutant human brain and Smarcc1 -mutant Xenopus brain exhibited similar alterationsin the expression of key transcription factors that regulate neural progenitor cell proliferation. Meaning: SMARCC1 is essential for human brain morphogenesis and is a bona fide CH risk gene. SMARCC1 mutations cause a novel human BAFopathy we term " S MARCC1- a ssociated D evelopmental D ysgenesis S yndrome (SaDDS)". These data implicate epigenetic dysregulation of fetal neural progenitors in the pathogenesis of hydrocephalus, with diagnostic and prognostic implications for patients and caregivers.

Molecular genetics of human developmental neurocranial anomalies: towards "precision surgery"

Recent trio-based whole-exome sequencing studies of congenital hydrocephalus and nonsyndromic craniosynostosis have identified multiple novel disease genes that have illuminated the pathogenesis of these disorders and shed new insight into the genetic regulation of human brain and skull development. Continued study of these and other historically understudied developmental anomalies has the potential to replace the current antiquated, anatomically based disease classification systems with a molecular nomenclature that may increase precision for genetic counseling, prognostication, and surgical treatment stratification-including when not to operate. Data will also inform future clinical trials, catalyze the development of targeted therapies, and generate infrastructure and publicly available data sets relevant for other related nonsurgical neurodevelopmental and neuropsychiatric diseases.