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Functional characterization of the MED12 p.Arg1138Trp variant in females: implications for neural development and disease mechanism.

BACKGROUND: Seven female individuals with multiple congenital anomalies, developmental delay and/or intellectual disability have been found to have a genetic variant of uncertain significance in the mediator complex subunit 12 gene (MED12 c.3412C>T, p.Arg1138Trp). The functional consequence of this genetic variant in disease is undetermined, and insight into disease mechanism is required. METHODS: We identified a de novo MED12 p.Arg1138Trp variant in a female patient and compared disease phenotypes with six female individuals identified in the literature. To investigate affected biological pathways, we derived two induced pluripotent stem cell (iPSC) lines from the patient: one expressing wildtype MED12 and the other expressing the MED12 p.Arg1138Trp variant. We performed neural disease modelling, transcriptomics and protein analysis, comparing healthy and variant cells. RESULTS: When comparing the two cell lines, we identified altered gene expression in neural cells expressing the variant, including genes regulating RNA polymerase II activity, transcription, pre-mRNA processing, and neural development. We also noted a decrease in MED12L expression. Pathway analysis indicated temporal delays in axon development, forebrain differentiation, and neural cell specification with significant upregulation of pre-ribosome complex gene pathways. CONCLUSION: In a human neural model, expression of MED12 p.Arg1138Trp altered neural cell development and dysregulated the pre-ribosome complex providing functional evidence of disease aetiology and mechanism in MED12-related disorders.

Humans

Formation of sensory maps: New tools reveal novel insights into neural development.

The development of functional neural circuits depends on the navigation of neurites (axons and dendrites) through spatially complex and molecularly diverse environments to their appropriate targets. How these processes maneuver through dense surroundings to reach their targets is a long-standing question in neuroscience. Studies of sensory systems have been especially enlightening for identifying cues that underlie connectivity due to their organization as stereotyped neural maps. Recent advances in imaging, connectomics, and genomics have profoundly deepened our understanding of these processes and uncovered new mechanisms regulating circuit development. In this review, we discuss studies of Drosophila sensory systems that provide new insights into axon and dendritic targeting, partner identification and selection, and subcellular refinement. We highlight related or divergent findings in other systems and provide an outlook for future studies.

Animals

Active learning of enhancers and silencers in the developing neural retina.

Deep learning is a promising strategy for modeling cis-regulatory elements. However, models trained on genomic sequences often fail to explain why the same transcription factor can activate or repress transcription in different contexts. To address this limitation, we developed an active learning approach to train models that distinguish between enhancers and silencers composed of binding sites for the photoreceptor transcription factor cone-rod homeobox (CRX). After training the model on nearly all bound CRX sites from the genome, we coupled synthetic biology with uncertainty sampling to generate additional rounds of informative training data. This allowed us to iteratively train models on data from multiple rounds of massively parallel reporter assays. The ability of the resulting models to discriminate between CRX sites with identical sequence but opposite functions establishes active learning as an effective strategy to train models of regulatory DNA. A record of this paper's transparent peer review process is included in the supplemental information.

Retina

Genetics of constant and severe pain in the NAPS2 cohort of recurrent acute and chronic pancreatitis patients.

Recurrent acute and chronic pancreatitis (RAP, CP) are complex, progressive inflammatory diseases with variable pain experiences impacting patient function and quality of life. The genetic variants and pain pathways in patients contributing to most severe pain experiences are unknown. We used previously genotyped individuals with RAP/CP from the North American Pancreatitis Study II (NAPS2) of European Ancestry for nested genome-wide associated study (GWAS) for pain-severity, chronicity, or both. Lead variants from GWAS were determined using FUMA. Loci with p<1e-5 were identified for post-hoc candidate identification. Transcriptome-wide association studies (TWAS) identified loci in cis and trans to the lead variants. Serum from phenotyped individuals with CP from the PROspective Evaluation of Chronic Pancreatitis for EpidEmiologic and Translational StuDies (PROCEED) was assessed for BDNF levels using Meso Scale Discovery Immunoassay. We identified four pain systems defined by candidate genes: 1) Pancreas-associated injury/stress mitigation genes include: REG gene cluster, CTRC, NEURL3 and HSF22. 2) Neural development and axon guidance tracing genes include: SNPO, RGMA, MAML1 and DOK6 (part of the RET complex). 3) Genes linked to psychiatric stress disorders include TMEM65, RBFOX1, and ZNF385D. 4) Genes in the dorsal horn pain-modulating BDNF/neuropathic pathway included SYNPR, NTF3 and RBFOX1. In an independent cohort BDNF was significantly elevated in patients with constant-severe pain. Extension and expansion of this exploratory study may identify pathway- and mechanism-dependent targets for individualized pain treatments in CP patients. PERSPECTIVE: Pain is the most distressing and debilitating feature of chronic pancreatitis. Yet many patients with chronic pancreatitis have little or no pain. The North American Pancreatitis Study II (NAPS2) includes over 1250 pancreatitis patients of all progressive stages with all clinical and phenotypic characteristics carefully recorded. Pain did not correlate well with disease stage, inflammation, fibrosis or other features. Here we spit the patients into groups with the most severe pain and/or chronic pain syndromes and compared them genetically with patients reporting mild or minimal pain. Although some genetic variants associated with pain were expressed in cells (1) of the pancreas, most genetic variants were linked to genes expressed in the nervous system cells associated with (2) neural development and axon guidance (as needed for the descending inhibition pathway), (3) psychiatric stress disorders, and (4) cells regulating sensory nerves associated with BDNF and neuropathic pain. Similar and overlapping genetic variants in systems 2 -4 are also seen in pain syndromes form other organs. The implications for treating pancreatic pain are great in that we can no longer focus on just the pancreas. Furthermore, new treatments designed for pain disorders in other tissues may be effective in some patient with pain syndromes from the pancreas. Further research is needed to replicate and extend these observations so that new, genetics-guided rational treatments can be developed and delivered.

Humans

Stem cell derived neural organoid approaches for neurological diseases.

Traditional two-dimensional cultures and animal models often fall short in capturing the complexities of neurodevelopmental and neurodegenerative diseases. However, recently developed neural organoid approaches, three-dimensional structures derived from human pluripotent stem cells, have become powerful tools for modeling human neuronal development and disease. Unlike traditional models, neural organoids provide significant insights and improved modeling capabilities. Here, we explore various types of neural organoids in disease modeling and outline distinct protocols for generating each type, including specific patterning methods, growth factors, and differentiation durations. The potential and advantages of co-culturing neural organoids with other cells and tissues are also discussed. While neural organoids have already made significant contributions to neuroscience research, future directions should focus on enhancing their maturation and functionality. The progression of neural organoids approaches will generate more accurate and comprehensive disease models, ultimately adding to our understanding of disease pathogenesis and paving the way for future precision therapies for neurological diseases.

neural differentiation

Kin17 promotes rDNA transcription, ribosomal biogenesis, and cortical lamination.

During brain development, neural progenitor cells (NPCs) undergo rapid division, necessitating efficient ribosomal biogenesis for proliferation. Yet, the regulatory mechanisms remain largely elusive. Here, we report that the DNA binding protein Kin17 exhibits development-dependent expression and plays a vital role in embryonic development. Complete loss of Kin17 in mice leads to embryonic lethality, while Kin17 depletion specifically in NPCs allows embryonic survival but results in reduced brain size and cortical lamination defects. Our findings demonstrate that these cortical malformation stems from impaired NPC proliferation and differentiation. Mechanistically, we show that Kin17 binds to the promoter region of rDNA, sequentially recruiting NCL and Polr1a, thereby promoting rDNA transcription. Consequently, Kin17 facilitates ribosome biogenesis and protein translation in NPCs. This study underscores a critical role of Kin17 in promoting rDNA transcription and ribosomal biogenesis in NPCs during brain development, which is essential for proper cortical lamination.

Animals

A conserved molecular logic for neurogenesis to gliogenesis switch in the cerebral cortex.

During development, neural stem cells in the cerebral cortex, also known as radial glial cells (RGCs), generate excitatory neurons, followed by production of cortical macroglia and inhibitory neurons that migrate to the olfactory bulb (OB). Understanding the mechanisms for this lineage switch is fundamental for unraveling how proper numbers of diverse neuronal and glial cell types are controlled. We and others recently showed that Sonic Hedgehog (Shh) signaling promotes the cortical RGC lineage switch to generate cortical oligodendrocytes and OB interneurons. During this process, cortical RGCs generate intermediate progenitor cells that express critical gliogenesis genes Ascl1, Egfr, and Olig2. The increased Ascl1 expression and appearance of Egfr+ and Olig2+ cortical progenitors are concurrent with the switch from excitatory neurogenesis to gliogenesis and OB interneuron neurogenesis in the cortex. While Shh signaling promotes Olig2 expression in the developing spinal cord, the exact mechanism for this transcriptional regulation is not known. Furthermore, the transcriptional regulation of Olig2 and Egfr has not been explored. Here, we show that in cortical progenitor cells, multiple regulatory programs, including Pax6 and Gli3, prevent precocious expression of Olig2, a gene essential for production of cortical oligodendrocytes and astrocytes. We identify multiple enhancers that control Olig2 expression in cortical progenitors and show that the mechanisms for regulating Olig2 expression are conserved between the mouse and human. Our study reveals evolutionarily conserved regulatory logic controlling the lineage switch of cortical neural stem cells.

Animals

Firemaster 550 differentially alters gene expression underlying synaptic function in amygdala of prairie voles after gestational or lactational exposure.

Neurodevelopmental disorders often share similar behavioral diagnostic criteria including socioemotional and cognitive deficits. The prairie vole is a uniquely suitable model to study these deficits because they demonstrate strong social affiliation, bi-parental care, and partner attachment. Previously, we have shown that developmental exposure to the flame-retardant mixture Firemaster 550 (FM 550) impairs socioemotional behavior in the prairie vole and alters underlying neuroanatomy and function. However, the mechanisms for impaired pair bonding in males and increased anxiety in females remain unknown, along with the specific critical window(s) of vulnerability. Herein, we exposed prairie vole dams to FM 550 during gestation or lactation, and performed bulk RNA-seq on the amygdala, a hub of socioemotional processing, in their adult offspring. Two mathematically orthogonal methods were utilized for analysis, a linear statistical method and an ensemble machine learning method, incorporating sex as a biological variable. Gene ontology (GO) pathway analysis was performed following both and results compared to identify potential mechanisms of toxicity. GO results indicated consistent expression changes in the Synapse cellular component in all conditions, and implicated glutamatergic signaling specifically. Additionally, gestational exposure (GE) altered genes underlying modulation of synaptic transmission and neural development, while lactational exposure (LE) impacted genes underlying synaptic plasticity, axon guidance, and mitophagy. Machine learning identified disruption of endocrine system development, regulation of biosynthetic processes in GE animals, and suppression of various neuroinflammatory genes across multiple groups. Finally, we performed RNA expression analysis using Nanostring and demonstrated stronger correlation with the differentially expressed genes (DEG) of interest in females than males. Overall, this study demonstrates both the intersecting and distinct impacts of FM 550 exposure on amygdalar gene expression depending on sex and timing of exposure.

Animals

Maternal immune activation disrupts epigenomic and functional maturation of cortical excitatory neurons.

Elevated levels of maternal pro-inflammatory cytokines following severe infection during gestation can disrupt offspring neural development and increase the risk of neurodevelopmental disorders. The viral mimetic Poly(I:C) reproduces the effects of gestational influenza exposure, leading to behavioral outcomes that recapitulate neurodevelopmental disorder phenotypes. Although Poly(I:C)-induced maternal immune activation (PIC-MIA) alters the epigenome, behavior and cognition of offspring in adulthood, it remains unclear when these changes occur and how MIA influences the epigenomic regulatory programming across the transition from embryonic development to the mature brain. Here, we examined the effects of PIC-MIA on the epigenomic maturation of the frontal cortex, focusing on excitatory neuron-specific DNA methylation and transcriptomic dynamics throughout perinatal development. Mid-gestation PIC-MIA disrupted development of the excitatory neuron transcriptome, with the largest alterations observed at birth. PIC-MIA altered the development of the mature DNA methylation program of excitatory neurons at thousands of genomic regulatory regions that normally gain or lose methylation during development. Transcription factor binding site analyses of these differentially methylated regions revealed a significant enrichment of Tbr1 motifs within hyper-methylated deep-layer neuron-specific regions at birth. Notably, transcriptional targets of Tbr1 were down-regulated at birth despite up-regulation of Tbr1 transcription, suggesting PIC-MIA uncouples Tbr1 expression from its regulatory function in deep-layer neurons. Electrophysiological recordings of intrinsic and firing properties further confirmed a lasting disruption in deep-layer neuronal activity. Our results suggest that mid-gestation MIA may alter the development of deep-layer neurons through an epigenomic blockade of Tbr1 function, thereby perturbing normal cortical circuit formation.

Journal Article

The genetic overlap between schizophrenia and major depression with cognitive function.

This study aimed to systematically dissect the shared genetic basis of schizophrenia (SCZ) and major depression (MD) with cognitive function. To investigate this, we integrated large-scale genome-wide association studies (GWAS) summary statistics for SCZ (N&#x2009;=&#x2009;175,799, [cases, 74,776; controls, 101,023]), MD (N&#x2009;=&#x2009;2,622,273 [cases, 550,355; controls, 2,071,918]) and four cognitive traits (reaction time, N&#x2009;=&#x2009;330,069; memory, N&#x2009;=&#x2009;112,067; verbal-numerical reasoning, N&#x2009;=&#x2009;36,035; educational attainment, N&#x2009;=&#x2009;111,114). Linkage disequilibrium (LD) score regression analysis revealed that SCZ showed significant negative genetic correlations with reaction time, memory, and verbal-numerical reasoning. MD showed negative genetic correlations with memory, verbal-numerical reasoning, and educational attainment. Bayesian colocalization analysis identified seven genomic regions with strong or supportive evidence between SCZ and cognitive function, and two genomic regions with supportive evidence between MD and cognitive function. Gene mapping and over representation analysis (ORA) indicated that SCZ-associated genes were primarily involved in pathways related to transport processes, and MD-associated genes were significantly enriched in pathways related to neural development. Through genetic correlation and colocalization analysis, this study elucidates the genetic overlap between SCZ and MD with cognitive function, providing a new perspective for related research.

Journal Article

Genomic insights into stroke recovery: cross-phenotype associations.

Stroke is a major cause of long-term disability with variable recovery. While clinical factors such as initial severity play a role, genetic factors are increasingly recognized as important contributors to stroke recovery. Genotype studies are generally focused on a single post-stroke behavioural domain, but some genes might relate to broad mechanisms of plasticity. This study therefore aimed to identify cross-phenotypic genetic variants associated across two or more stroke recovery domains. DNA from Stroke, Stress, Rehabilitation, and Genetics study participants was genotyped, resulting in 9 814 610 variants. In order to examine cross-phenotypic results, we first conducted genome-wide association studies on the six recovery domains: motor (grip force), cognition (Telephone Montreal Cognitive Assessment), depression (Patient Health Questionnaire-8), stress (Primary Care Post-Traumatic Stress Disorder Screen), functional status (Stroke Impact Scale-Activities of Daily Living), and disability (modified Rankin Scale 0-2 versus 3-6), some of which were tested longitudinally, yielding nine phenotypes. Models were adjusted for age, sex, initial severity (NIH Stroke Scale score), and ancestry. Cross-phenotype associations were identified by evaluating single nucleotide polymorphisms (SNPs) associated (P < 5e-5) with multiple phenotypes. To determine how these genetic variants may relate to biological mechanisms of recovery, we conducted gene enrichment analyses. Participants (n = 565, 59% male) had mild-moderate initial stroke severity (median acute NIH Stroke Scale score = 4). After accounting for the correlation structure among the nine phenotypes, we observed 319 cross-phenotypic SNPs, 3.45 times the expected number. Five of the cross-phenotypic SNPs were linked to genes relevant to neural development, function and plasticity, e.g. ERICH1 (rs11778883-C), FOX3 (rs55726768-G), LIFR-AS1 (rs76401391-T), RPS6KA2 (rs113518460-C) and TUBGCP2 (rs147150392-C), as were enrichments in RAB5-EEA1, CTNNA1-CTNNB1, CIN85-SH3GL2 and ELMO1-DOCK2 complexes. Multiple gene enrichments were found, e.g. Stroke Impact Scale-Activities of Daily Living and Patient Health Questionnaire 8 at 3 months were enriched for CREB phosphorylation, which is important for long-term potentiation. We identified cross-phenotypic SNPs associated with multiple behavioural domains of stroke recovery. Some of these genes encode, or regulate, druggable proteins. These genetic factors are not well captured by clinical or neuroimaging assessments and so provide a unique window into stroke recovery. These findings, if validated, suggest that some genes may be broadly important to stroke recovery.

GWAS

Maternal Immune Activation Disrupts Epigenomic and Functional Maturation of Cortical Excitatory Neurons.

Elevated levels of maternal pro-inflammatory cytokines during gestation can disrupt offspring neural development, increasing the risk of neurodevelopmental disorders. We studied the effects of Poly(I:C)-induced maternal immune activation (PIC-MIA) during mid-gestation on developing cortical excitatory neurons' DNA methylation and transcriptome. PIC-MIA disrupted the developmental regulation of synapse-related genes and of genes implicated in autism spectrum disorders. Genomic regions that gain or lose DNA methylation during normal development were altered following PIC-MIA, including neurodevelopmental transcription factor binding sites. The DNA methylation and transcriptional changes were consistent with a delay in excitatory neuron maturation. Whole-cell recordings showed that PIC-MIA preferentially altered the physiological development of layer 5 excitatory neurons. Taken together, present results suggest that alterations in the epigenome, through the disruption of circuit formation, may drive the long-term consequences of maternal infection during gestation.

DNA methylation

Genome reorganisation and expansion shape 3D genome architecture and define a distinct regulatory landscape in coleoid cephalopods.

How genomic changes translate into organismal novelties is often confounded by the multi-layered nature of genome architecture and the long evolutionary timescales over which molecular changes accumulate. Coleoid cephalopods (squid, cuttlefish, and octopus) provide a unique system to study these processes due to a large-scale chromosomal rearrangement in the coleoid ancestor that resulted in highly modified karyotypes, followed by lineage-specific fusions, translocations, and repeat expansions. How these events have shaped gene regulatory patterns underlying the evolution of coleoid innovations, including their large and elaborately structured nervous systems, novel organs, and complex behaviours, remains poorly understood. To address this, we integrate Micro-C, RNA-seq, and ATAC-seq across multiple coleoid species, developmental stages, and tissues. We find that while topological compartments are broadly conserved, hundreds of chromatin loops are species- and context-specific, with distinct regulation signatures and dynamic expression profiles. CRISPR-Cas9 knockout of a putative regulatory sequence within a conserved region demonstrates the role of loops in neural development and the prevalence of long-range, inter-compartmental interactions. We propose that differential evolutionary constraints across the coleoid 3D genome allow macroevolutionary processes to shape genome topology in distinct ways, facilitating the emergence of novel regulatory entanglements and ultimately contributing to the evolution and maintenance of complex traits in coleoids.

Journal Article

Neural and endocrine development after chronic tryptophan deficiency in rats: I. Brain monoamine and pituitary responses.

Caloric restriction and tryptophan deficient diets have been shown to delay aging in the immature laboratory rat. Studies of monoamine levels in the brain of developing female rats fed on these diets show changes in serotonin but not norepinephrine or dopamine levels: in tryptophan-restricted rats serotonin levels were reduced in all brain areas studied, whereas in caloric-restricted animals serotonin levels were increased in the cerebral hemispheres only. Another group of animals, in which growth and maturation was delayed by feeding d,1-parachlorophenylalanine (PCPA) showed decreases in serotonin, norepinephrine and dopamine concentrations in all brain regions investigated. All treatments employed to arrest growth and maturation resulted in pituitary alterations manifested by gross, histological and ultrastructural changes. It is postulated that there maturation- and age-retarding treatments delay the development of the central nervous system resulting in postponed maturation of the neuroendocrine axis, with consequent hypoactivity of certain pituitary functions and a resultant delay in the onset of maturation and senescence.

Animals

A mouse organoid platform for modeling cerebral cortex development and cis-regulatory evolution in vitro.

Natural selection has shaped the gene regulatory networks that orchestrate cortical development, leading to structural and functional variation across mammals, but the molecular and cellular mechanisms underpinning these changes have only begun to be characterized. Here, we develop a reproducible protocol for cerebral cortex organoid generation from mouse epiblast stem cells (EpiSCs), which recapitulates the timing and cellular differentiation programs of the embryonic cortex. We generated cortical organoids from F1 hybrid EpiSCs derived from crosses between laboratory mice (C57BL/6J) and four wild-derived inbred strains spanning &#x223c;1 M years of evolutionary divergence to comprehensively map cis-acting transcriptional regulatory variation across developing cortical cell types, using single-cell RNA sequencing (scRNA-seq). We identify hundreds of genes that exhibit dynamic allelic imbalances, providing the first insight into the developmental mechanisms underpinning changes in cortical structure and function between subspecies. These experimental methods and cellular resources represent a powerful platform for investigating gene regulation in the developing cerebral cortex.

Organoids

Decreased H3K79 acetylation and dysregulation of neurodevelopmental genes in fetal down syndrome.

BACKGROUND: Down syndrome (DS), the most prevalent chromosomal disorder caused by trisomy 21, manifests intellectual disability and cognitive dysfunction. Cumulative studies confirm epigenetic pathways including DNA methylation and non-coding RNAs drive DS pathological progression. Histone post-translational modifications (PTMs) are core epigenetic regulators of fetal brain development. However, genome-wide PTM alterations and their downstream functions in fetal DS brains remain poorly characterized, leaving a key gap in revealing epigenetic mechanisms underlying DS neurodevelopmental defects. To address this, we aimed to establish the first comprehensive landscape of histone PTMs in fetal DS cortex and investigate whether specific PTM changes contribute to aberrant neurodevelopmental gene expression. METHODS: Fetal cortexs from control and DS groups were subjected to global histone modification profiling via high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). We detected mono-, di-, and tri-methylation, acetylation, homocysteinylation and malonylation on all four core histones (H2A, H2B, H3, H4). Chromatin immunoprecipitation sequencing (ChIP-seq) was used to map genomic binding profiles of H3 lysine 79 acetylation (H3K79ac). Quantitative reverse transcription polymerase chain reaction (qRT-PCR) was performed to quantify mRNA levels of candidate neurodevelopmental genes. RESULTS: HPLC-MS/MS analysis identified 172 distinct histone PTMs in control fetal cortices and 168 PTMs in DS fetal cortical samples. Quantitative comparison of 22 quantifiable histone PTMs revealed that H3K79ac showed the most prominent reduction in DS samples, with a 34% decrease (P<0.05). Chromatin immunoprecipitation (ChIP)-seq verified specific H3K79ac occupancy at the genomic loci of three vital neurodevelopmental genes: TNFSF13B, NXPH1 and CAMK4. Correspondingly, qRT-PCR revealed aberrant transcription levels of these three genes in DS fetal cortices. CONCLUSIONS: This study establishes the first quantitative landscape of histone PTMs in in DS fetal cortical tissues. We demonstrate that depleted H3K79ac acts as a candidate epigenetic driver of DS neuropathology by disrupting the transcription of critical neurodevelopmental genes. This work reveals a novel epigenetic mechanism and a promising therapeutic target for DS-related neurodevelopmental disorders.

Down syndrome (DS)