Biology subjects

Bjornsson, H. T.

Publications and source records attributed to Bjornsson, H. T..

At least 19 recordsLinked to original sources

bioRxiv2026

SARAF represses the mild hypothermia response through the regulation of JUN

The mild hypothermia response (MHR) is a conserved mammalian cytoprotective program activated upon exposure to mild hypothermia (32 degrees C) that contributes to the neuroprotective effects of therapeutic hypothermia following hypoxic injury. Although rapid changes in intracellular calcium occur upon cooling, the mechanisms linking calcium dynamics to the activation of core MHR factors such as SP1 and RBM3 remain incompletely defined. In this study, we used siRNA-mediated knockdown (KD) of candidate regulators in conjunction with novel mild hypothermia indicator (MHI) reporters to identify upstream modulators of MHR-associated transcription. We identify SARAF, a negative regulator of store-operated calcium entry (SOCE), as a repressor of both SP1 and RBM3 under normothermic conditions. SARAF depletion is associated with increased intracellular calcium release and enhanced SP1- and RBM3-linked transcriptional outputs. We identify JUN as an important downstream factor mediating SARAF depletion-dependent de-repression of the MHR and demonstrate that it undergoes activation rapidly upon cooling. Finally, SARAF depletion conferred significant cytoprotection against hypoxia-induced early apoptosis. Collectively, these findings establish SARAF as an upstream regulator of MHR-associated transcription and provide a functional link between cold-induced intracellular calcium dynamics and the induction of core MHR effectors.

molecular biology↗

bioRxiv2026

Loss of KMT2D accelerates hypertrophic chondrocyte differentiation and senescence by increasing mitochondrial ROS production

Longitudinal bone growth occurs through endochondral ossification, which is accompanied by the differentiation of chondrocytes in the growth plate. Disruption in chondrocyte maturation can lead to skeletal growth abnormalities, such as those observed in Kabuki syndrome type 1 (KS1), a genetic disorder caused by heterozygous pathogenic variants in the KMT2D gene. KS1 patients exhibit postnatal growth deficiency, craniofacial hypoplasia, and skeletal deformities, yet the mechanisms underlying these phenotypic manifestations remain poorly understood. Our study investigated the effects of KMT2D deficiency on chondrocyte maturation and identified premature chondrocyte hypertrophy as a key driver of skeletal abnormalities in KS1. We previously observed reduced femur and tibia length in a KS1 mouse model, along with altered growth plate architecture, particularly affecting the heights of the proliferative and hypertrophic zones. Here, we show that KMT2D-deficient chondrocytes exhibit accelerated differentiation and early senescence upon exposure to supraphysiological oxygen levels (20% O2). These pathological changes were linked to increased mitochondrial reactive oxygen species (ROS) production likely caused by deficiencies in electron transport chain function, leading to oxidative stress and premature hypertrophy. Pharmacological ROS neutralization or hypoxic conditions mitigated these effects, restoring normal chondrocyte differentiation and preventing premature ossification. These findings demonstrate that KMT2D loss induces oxidative stress-driven chondrocyte hypertrophy, disrupting the balance of cartilage growth and ossification. Our study provides crucial mechanistic insights into KS1-associated skeletal abnormalities and suggests mitochondrial ROS regulation as a potential therapeutic avenue.

molecular biology↗

bioRxiv2025

A patient derived missense mouse model of Kabuki syndrome 1

Kabuki syndrome (KS) is a rare cause of intellectual disability resulting from heterozygous pathogenic variants in the gene encoding the histone methyltransferase KMT2D. A previously established loss-of-function mouse model of KS exhibits key phenotypic features, and therapeutic trials in this mouse model suggest postnatal malleability of neurological symptoms. However, 15-30% of individuals with KS, carry missense variants. To investigate whether missense variants lead to similar phenotypic presentation in mice, we used CRISPR-Cas9 to introduce the KS patient variant R5230H into C57BL/6NTac. Computational and in vitro testing suggests that the R5230H variant does not impair protein stability or loss of enzyme function of KMT2D. Despite a distinct mechanistic basis, our new mouse model (Kmt2d+/R5230H) recapitulates most phenotypes of our prior loss-of-function model, including growth deficiency, craniofacial anomalies, and IgA deficiency but not altered neurological function. Kmt2d+/R5230Hmice show perinatal lethality and a high frequency of unilateral kidney agenesis, a novel phenotype in KS mouse models. Kmt2d+/R5230H mice provide a unique opportunity to understand the impact of missense variants on KMT2D function and uncover developmental and perinatal abnormalities in KS. Summary statementA novel Kabuki syndrome missense mouse model with intact KMT2D enzymatic function shares most features with prior KS models, except disruption of adult neurogenesis, and exhibits novel unilateral kidney loss.

genetics↗

bioRxiv2025

Chaperone AIP Couples mTORC1 Activation and Catabolic Metabolism During Neonatal Development

To grow and divide cells must tightly coordinate anabolic programs with the availability of nutrients and growth factors. This balance is especially critical during postnatal development, when biosynthetic and energetic demands are high, and nutrient supply and neonates have to adapt to periods of fasting. These conditions place acute stress on the proteostasis network, making autophagy essential for nutrient recycling. We found that the chaperone aryl hydrocarbon receptor-interacting protein (AIP) supports both arms of this metabolic balance: promoting anabolic PI3K-AKT signaling for mTORC1 activation and enabling catabolic processes such as proteasomal degradation and autophagy. Loss of AIP causes a severe neonatal metabolic disorder, where affected infants fail to thrive postnatally. Our findings establish AIP as a central regulator of neonatal metabolic adaptation and cellular homeostasis. One Sentence SummaryAIP integrates nutrient sensing and protein recycling to sustain neonatal survival.

developmental biology↗

bioRxiv2025

Shared molecular consequences of epigenetic machinery disruption in neuronal progenitors

The Mendelian disorders of the epigenetic machinery (MDEMs) are an emerging cause of intellectual disability and growth abnormalities, which commonly disrupt hippocampal function. To investigate consequences of epigenetic machinery (EM) disruption during neurodevelopment, we systematically knocked out (KO) EM factors in neuronal progenitors isolated from the murine hippocampus and established a neurodifferentiation model to interrogate their functions. We then profiled gene expression and DNA methylation (DNAm) in the EM-KOs using RNA sequencing and Nanopore long-read DNA sequencing. While Dnmt1-KO induced extensive DNAm alterations, Kmt2a-KO had little effect on methylation. Nevertheless, the disruption of Kmt2a and Dnmt1 produced strikingly convergent transcriptional changes. Loss of either EM factor led to premature neuronal differentiation, partially explaining this convergence, and MYC appeared as a shared regulatory node linked to downregulation of cell-cycle programs in these cells. Extending our methylation analysis to 46 EM genes, we found that loss of DNA methyltransferases induced the strongest DNAm changes, whereas other EM-KOs had subtle or negligible effects. However, clustering of EM-KOs based on promoter DNAm levels revealed three distinct EM subgroups, of which two were enriched for interactions with the DNAm machinery. Allele-specific analysis of DNAm further identified a single differentially methylated region shared across the 46 EM-KOs, localized to the FVB allele over the Zic4 3UTR. Furthermore, Zic4 overexpression appears to maintain the neuronal progenitor state, suggesting functional relevance of this locus. Taken together, our results reveal both gene-specific and convergent effects across diverse EM-KOs and provide new insight into the molecular etiology of the MDEMs.

genomics↗

bioRxiv2024

Biallelic Loss of Molecular Chaperone Molecule AIP Results in a Novel Severe Multisystem Disease Defined by Defective Proteostasis

Children born with deleterious biallelic variants of the chaperone aryl hydrocarbon receptor interacting protein (AIP) have a novel pediatric metabolic disease presenting a severe, complex clinical phenotype characterized by failure to develop following birth. Analysis of Aip knockout mouse embryonic fibroblasts and patient-derived dermal fibroblasts revealed that AIP was required to support proteostasis; including proteasome activity, induction of autophagy and lysosome function. aip knockout zebrafish, recapitulated the phenotype of the children; dying at an early stage of development when autophagy is required to adapt to periods of starvation. Our results demonstrate that AIP plays a crucial role in initiating autophagy and maintaining proteostasis in vitro and in vivo. One Sentence SummaryHomozygous loss of the chaperone AIP results in a novel pediatric disease exhibiting multiple features of a lysosomal storage disease.

molecular biology↗

bioRxiv2024

In-utero rescue of neurological dysfunction in a mouse model of Wiedemann-Steiner syndrome

Wiedemann-Steiner syndrome (WDSTS) is a rare genetic cause of intellectual disability primarily caused by heterozygous loss of function variants in the gene encoding the histone methyltransferase KMT2A. Prior studies have shown successful postnatal amelioration of disease phenotypes for Rett, Rubinstein-Taybi and Kabuki syndromes, related Mendelian disorders of the epigenetic machinery. To explore whether the neurological phenotype in WDSTS is treatable in-utero, we created a novel mouse model carrying a loss of function variant in between two loxP sites. Kmt2a+/LSL mice demonstrate core features of WDSTS including growth retardation, craniofacial abnormalities, and hypertrichosis as well as hippocampal memory defects. The neurological phenotypes show rescue upon restoration of KMT2A in-utero following breeding to a nestin-Cre. Together, our data provide a novel mouse model to explore the therapeutic window in WDSTS. Our work suggests that WDSTS has a window of opportunity extending at least until the mid-point of in-utero development, making WDSTS an ideal candidate for future therapeutic strategies. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=133 SRC="FIGDIR/small/604339v1_ufig1.gif" ALT="Figure 1"> View larger version (40K): org.highwire.dtl.DTLVardef@1b913caorg.highwire.dtl.DTLVardef@1c23ce3org.highwire.dtl.DTLVardef@12b8a25org.highwire.dtl.DTLVardef@17a9a4e_HPS_FORMAT_FIGEXP M_FIG Graphical abstract C_FIG

genetics↗

bioRxiv2023

Growth retardation in a mouse model of Kabuki syndrome 2 bears mechanistic similarities to Kabuki syndrome 1

Growth retardation is a characteristic feature of both Kabuki syndrome 1 (KS1) and Kabuki syndrome 2 (KS2), Mendelian disorders of the epigenetic machinery with similar phenotypes but distinct genetic etiologies. We previously described skeletal growth retardation in a mouse model of KS1 and further established that a Kmt2d-/- chondrocyte model of KS1 exhibits precocious differentiation. Here we characterized growth retardation in a mouse model of KS2, Kdm6atm1d/+. We show that Kdm6atm1d/+ mice have decreased femur and tibia length compared to controls and exhibit abnormalities in cortical and trabecular bone structure. Kdm6atm1d/+ growth plates are also shorter, due to decreases in hypertrophic chondrocyte size and hypertrophic zone height. Given these disturbances in the growth plate, we generated Kdm6a-/- chondrogenic cell lines. Similar to our prior in vitro model of KS1, we found that Kdm6a-/- cells undergo premature, enhanced differentiation towards chondrocytes compared to Kdm6a+/+ controls. RNA-seq showed that Kdm6a-/- cells have a distinct transcriptomic profile that indicates dysregulation of cartilage development. Finally, we performed RNA-seq simultaneously on Kmt2d-/-, Kdm6a-/-, and control lines at Days 7 and 14 of differentiation. This revealed surprising resemblance in gene expression between Kmt2d-/- and Kdm6a-/- at both time points and indicates that the similarity in phenotype between KS1 and KS2 also exists at the transcriptional level.

genetics↗

bioRxiv2023

Neuron-specific chromatin disruption at CpG islands and aging-related regions in Kabuki syndrome mice

Many Mendelian developmental disorders caused by coding variants in epigenetic regulators have now been discovered. Epigenetic regulators are broadly expressed, and each of these disorders typically exhibits phenotypic manifestations from many different organ systems. An open question is whether the chromatin disruption - the root of the pathogenesis - is similar in the different disease-relevant cell types. This is possible in principle, since all these cell-types are subject to effects from the same causative gene, that has the same kind of function (e.g. methylates histones) and is disrupted by the same germline variant. We focus on mouse models for Kabuki syndrome types 1 and 2, and find that the chromatin accessibility abnormalities in neurons are mostly distinct from those in B or T cells. This is not because the neuronal abnormalities occur at regulatory elements that are only active in neurons. Neurons, but not B or T cells, show preferential chromatin disruption at CpG islands and at regulatory elements linked to aging. A sensitive analysis reveals that the regions disrupted in B/T cells do exhibit chromatin accessibility changes in neurons, but these are very subtle and of uncertain functional significance. Finally, we are able to identify a small set of regulatory elements disrupted in all three cell types. Our findings reveal the cellular-context-specific effect of variants in epigenetic regulators, and suggest that blood-derived "episignatures" may not be well-suited for understanding the mechanistic basis of neurodevelopment in Mendelian disorders of the epigenetic machinery.

genomics↗

bioRxiv2023

Novel mouse model of Weaver syndrome displays overgrowth and excess osteogenesis reversible with KDM6A/6B inhibition

Weaver syndrome is a Mendelian disorder of the epigenetic machinery (MDEM) caused by germline pathogenic variants in EZH2, which encodes the predominant H3K27 methyltransferase and key enzymatic component of Polycomb repressive complex 2 (PRC2). Weaver syndrome is characterized by striking overgrowth and advanced bone age, intellectual disability, and distinctive facies. We generated a mouse model for the most common Weaver syndrome missense variant, EZH2 p.R684C. Ezh2R684C/R684C mouse embryonic fibroblasts (MEFs) showed global depletion of H3K27me3. Ezh2R684C/+ mice had abnormal bone parameters indicative of skeletal overgrowth, and Ezh2R684C/+ osteoblasts showed increased osteogenic activity. RNA-seq comparing osteoblasts differentiated from Ezh2R684C/+and Ezh2+/+ bone marrow mesenchymal stem cells (BM-MSCs) indicated collective dysregulation of the BMP pathway and osteoblast differentiation. Inhibition of the opposing H3K27 demethylases Kdm6a/6b substantially reversed the excessive osteogenesis in Ezh2R684C/+ cells both at the transcriptional and phenotypic levels. This supports both the ideas that writers and erasers of histone marks exist in a fine balance to maintain epigenome state, and that epigenetic modulating agents have therapeutic potential for the treatment of MDEMs.

genetics↗

bioRxiv2022

KMT2D regulates thymic egress by modulating maturation and integrin expression

ObjectiveThere is a clinical need to understand how dysregulated thymocyte development, caused by pathogenic variants in the gene encoding the histone-modifying enzyme, lysine methyltransferase 2D (KMT2D), contributes to immune dysfunction, including immune deficiency, autoimmunity, and lymphoproliferative sequela, and immune-driven mortality in individuals with Kabuki syndrome type 1 (KS1). MethodsWe studied peripheral T cells and thymocytes in both individuals with KS1 and murine constitutive and conditional targeted Kmt2d in T cells and hematopoietic lineages. KMT2D target genes, identified by RNA-sequencing of murine Kmt2d-knockout single-positive thymocytes, were validated with H3K4me3 ChIP-PCR and flow cytometry. ResultsRecent thymic emigrant (RTE) and naive T cells were reduced, and memory and double-negative (DN)-T cells were expanded in human KS1 and murine models. Kmt2d loss led to Mature 1 CD8+-single positive (SP) thymocyte accumulation and a decrease in SP thymocyte egress licensing expression (normally associated with the Mature 2 phenotype). Splenomegaly is associated with hematopoietic-driven Kmt2d loss and brings to light potential overlapping phenotypes with lymphoproliferative syndromes. Finally, we identified a KMT2D-regulated cluster of integrins which likely mediates aspects of the T cell egression. ConclusionsSingle-positive thymocyte populations deficient in Kmt2d display less integrin, less maturation, and less egress licensing gene expression; thereby, altering the downstream peripheral T cell composition that contribute to the observed KS1-associated immune deficiency. T cell intrinsic Kmt2d loss increases the percentage of peripheral DNT cells potentially through dysregulated apoptotic signaling, while hematopoietic-driven Kmt2d loss predisposes to splenomegaly; therefore, loss of Kmt2d recapitulates several distinct features of lymphoproliferative syndromes.

immunology↗

bioRxiv2021

Universal prediction of cell cycle position using transfer learning

BackgroundThe cell cycle is a highly conserved, continuous process which controls faithful replication and division of cells. Single-cell technologies have enabled increasingly precise measurements of the cell cycle both as a biological process of interest and as a possible confounding factor. Despite its importance and conservation, there is no universally applicable approach to infer position in the cell cycle with high-resolution from single-cell RNA-seq data. ResultsHere, we present tricycle, an R/Bioconductor package, to address this challenge by leveraging key features of the biology of the cell cycle, the mathematical properties of principal component analysis of periodic functions, and the use of transfer learning. We estimate a cell cycle embedding using a fixed reference dataset and project new data into this reference embedding; an approach that overcomes key limitations of learning a dataset dependent embedding. Tricycle then predicts a cell-specific position in the cell cycle based on the data projection. The accuracy of tricycle compares favorably to gold-standard experimental assays, which generally require specialized measurements in specifically constructed in vitro systems. Using internal controls which are available for any dataset, we show that tricycle predictions generalize to datasets with multiple cell types, across tissues, species and even sequencing assays. ConclusionsTricycle generalizes across datasets, is highly scalable and applicable to atlas-level single-cell RNA-seq data.

genomics↗

bioRxiv2020

Leveraging the Mendelian Disorders of the Epigenetic Machinery to Systematically Map Functional Epigenetic Variation

The Mendelian Disorders of the Epigenetic Machinery (MDEMs) have emerged as a class of Mendelian disorders caused by loss-of-function variants in epigenetic regulators. Although each MDEM has a different causative gene, they exhibit several overlapping disease manifestations. Here, we hypothesize that this phenotypic convergence is a consequence of common abnormalities at the epigenomic level, which directly or indirectly lead to downstream convergence at the transcriptomic level. Therefore, we seek to identify abnormalities shared across multiple MDEMs, in order to pinpoint locations where epigenetic variation is causally related to disease phenotypes. To this end, we perform a comprehensive interrogation of chromatin (ATAC-Seq) and expression (RNA-Seq) states in B cells from mouse models of three MDEMs (Kabuki types 1&2 and Rubinstein-Taybi syndromes). We build on recent work in covariate-powered multiple testing to develop a new approach for the overlap analysis, which enables us to find extensive overlap primarily localized in gene promoters. We show that disruption of chromatin accessibility at promoters often leads to disruption of downstream gene expression, and identify 463 loci and 249 genes with shared disruption across all three MDEMs. As an example of how widespread dysregulation leads to specific phenotypes, we show that subtle expression alterations of multiple, IgA-relevant genes, collectively contribute to IgA deficiency in KS1 and RT1. In contrast, we predict that KS2 does not have IgA deficiency, and confirm this observation in vivo. We propose that the joint study of MDEMs offers a principled approach for systematically mapping functional epigenetic variation in mammals.

genetics↗

bioRxiv2020

Purifying selection acts on germline methylation to modify the CpG mutation rate at promoters

In the study of molecular features like epigenetic marks, it is appealing to ascribe observed patterns to the action of natural selection. However, this conclusion requires a test for selection based on a well-defined notion of neutrality. Here, focusing on epigenetic marks at gene loci, we formalize what it means for an epigenetic mark to be neutral, and develop a test for selection. Our test respects the foundational aspect of epigenetics: trans-regulation by transcription factors and chromatin modifiers. It also enables adjustment for confounders. We establish that promoter DNA methylation, promoter H3K4me3 and exonic H3K36me3 are all under selection, and that this is unlikely to be a passive consequence of selection on gene expression. The effect of these epigenetic marks on fitness is arguably partly explained by a causal involvement in gene regulation. However, we also investigate the complementary explanation that DNA methylation and H3K36me3 are under selection in part because they modify the mutation rate of important genomic regions. We show that this explanation is consistent with empirical observations as well as population genetics theory, because of the trans-regulation. Exemplifying the protection of important regions from high mutability, we demonstrate that in humans the more intolerant to loss-of-function mutations a gene is, the lower its coding mutation rate is. Our framework for selection inference is simple but general, and we speculate that its core ideas will be useful for additional molecular features beyond epigenetic marks.

evolutionary biology↗

bioRxiv2020

Inhibition of KDM1A activity restores adult neurogenesis and improves hippocampal memory in a mouse model of Kabuki syndrome

Kabuki syndrome (KS) is a rare cause of intellectual disability primarily caused by loss of function mutations in lysine-specific methyltransferase 2D (KMT2D), which normally adds methyl marks to lysine 4 on histone 3. Previous studies have shown that a mouse model of KS (Kmt2d+/{beta}Geo) demonstrates disruption of adult neurogenesis and hippocampal memory. Proof-of-principle studies have shown postnatal rescue of neurological dysfunction following treatments that promote chromatin opening, however, these strategies are non-specific and do not directly address the primary defect of histone methylation. Since lysine-specific demethylase 1A (LSD1/KDM1A) normally removes the H3K4 methyl marks added by KMT2D, we hypothesize that inhibition of KDM1A demethylase activity may ameliorate molecular and phenotypic defects stemming from KMT2D loss. To test this hypothesis, we evaluated a recently developed KDM1A inhibitor (TAK-418) in Kmt2d+/{beta}Geo mice. We find that orally administered TAK-418 increases the numbers of newly born Doublecortin (DCX)+ cells and processes in hippocampus in a dose dependent manner. We also observe TAK-418-dependent rescue of histone modification defects in hippocampus both by Western blot and ChIP-Seq. Treatment rescues gene expression abnormalities including those of immediate early genes such as FBJ osteosarcoma oncogene (Fos) and FBJ osteosarcoma oncogene homolog B (Fosb). After 2 weeks of TAK-418, Kmt2d+/{beta}Geo mice demonstrate normalization of hippocampal memory defects. In summary, our data suggest that KDM1A inhibition is a plausible treatment strategy for KS and support the hypothesis that the epigenetic dysregulation secondary to KMT2D dysfunction plays a major role in the postnatal neurological disease phenotype in KS.

genetics↗

bioRxiv2020

Promoter CpG density is predictive of downstream gene loss-of-function intolerance

The aggregation and joint analysis of large numbers of exome sequences has recently made it possible to de-rive estimates of intolerance to loss-of-function (LoF) variation for human genes. Here, we demonstrate strong and widespread coupling between genic LoF-intolerance and promoter CpG density across the human genome. Genes downstream of the most CpG-rich pro-moters (top 10% CpG density) have a 67.2% probability of being highly LoF-intolerant, using the LOEUF metric from gnomAD. This is in contrast to 7.4% of genes downstream of the most CpG-poor (bottom 10% CpG density) promoters. Combining promoter CpG density with exonic and promoter conservation explains 33.4% of the variation in LOEUF, and the contribution of CpG density exceeds the individual contributions of exonic and promoter conservation. We leverage this to train a simple and easily interpretable predictive model that out-performs other existing predictors and allows us to classify 1,760 genes - which currently lack reliable LOEUF estimates - as highly LoF-intolerant or not. These predictions have the potential to aid in the interpretation of novel patient variants. Moreover, our results reveal that high CpG density is not merely a generic feature of human promoters, but is preferentially encountered at the promoters of the most selectively constrained genes, calling into question the prevailing view that CpG islands are not subject to selection.

genetics↗

bioRxiv2019

Precocious Chondrocyte Differentiation Disrupts Skeletal Growth in Kabuki Syndrome Mice

Kabuki syndrome 1 (KS1) is a Mendelian disorder of the epigenetic machinery caused by mutations in the gene encoding KMT2D, which methylates lysine 4 on histone H3 (H3K4). KS1 is characterized by intellectual disability, postnatal growth retardation, and distinct craniofacial dysmorphisms. A mouse model (Kmt2d+/ {beta} Geo) exhibits features of the human disorder and has provided insight into other phenotypes; however, the mechanistic basis of skeletal abnormalities and growth retardation remains elusive. Using high-resolution micro-computed tomography we show that Kmt2d+/{beta}Geo mice have shortened long bones and ventral bowing of skulls. In vivo expansion of growth plates within both the skull and long bones suggests disrupted endochondral ossification as a common disease mechanism. Stable chondrocyte cell lines harboring inactivating mutations in Kmt2d exhibit increased proliferation and differentiation, which further supports this mechanism. A known inducer of chondrogenesis, SOX9, and its targets show markedly increased expression in Kmt2d-/- chondrocytes. By transcriptome profiling, we identify Shox2 as a putative KMT2D target. We propose that decreased KMT2D-mediated H3K4me3 at Shox2 releases Sox9 inhibition and thereby leads to enhanced chondrogenesis, providing a novel and plausible explanation for precocious chondrocyte differentiation. Our findings not only provide insight into the pathogenesis of growth retardation in KS1, but also suggest novel therapeutic targets to rescue growth retardation in KS1 and related disorders.

genetics↗

bioRxiv2018

Transcriptional suppression from KMT2D loss disrupts cell cycle and hypoxic responses in neurodevelopmental models of Kabuki syndrome

Chromatin modifiers act to coordinate gene expression changes critical to neuronal differentiation from neural stem/progenitor cells (NSPCs). Lysine-specific methyltransferase 2D (KMT2D) encodes a histone methyltransferase that promotes transcriptional activation, and is frequently mutated in cancers and in the majority (>70%) of patients diagnosed with the congenital, multisystem intellectual disability (ID) disorder Kabuki syndrome 1 (KS1). Critical roles for KMT2D are established in various non-neural tissues, but the effects of KMT2D loss in brain cell development have not been described. We conducted parallel studies of proliferation, differentiation, transcription, and chromatin profiling in KMT2D-deficient human and mouse models to define KMT2D-regulated functions in neurodevelopmental contexts, including adult-born hippocampal NSPCs in vivo and in vitro. We report cell-autonomous defects in proliferation, cell cycle, and survival, accompanied by early NSPC maturation in several KMT2D-deficient model systems. Transcriptional suppression in KMT2D-deficient cells indicated strong perturbation of hypoxia-responsive metabolism pathways. Functional experiments confirmed abnormalities of cellular hypoxia responses in KMT2D-deficient neural cells, and accelerated NSPC maturation in vivo. Together, our findings support a model in which loss of KMT2D function suppresses expression of oxygen-responsive gene programs important to neural progenitor maintenance, resulting in precocious neuronal differentiation in a mouse model of KS1.\n\nGraphical Abstract\n\nO_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=91 SRC=\"FIGDIR/small/484410v3_ufig1.gif\" ALT=\"Figure 1\">\nView larger version (22K):\norg.highwire.dtl.DTLVardef@55dd1aorg.highwire.dtl.DTLVardef@1270c80org.highwire.dtl.DTLVardef@a5bda2org.highwire.dtl.DTLVardef@144df37_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗