Biology subjects

Anastassiadis, K.

Publications and source records attributed to Anastassiadis, K..

8 recordsLinked to original sources

bioRxiv2025

A non-catalytic role for MLL2 in controlling chromatin organisation and mobility during the priming of pluripotent cells for differentiation

How the chromatin regulator MLL2 (KMT2B) influences cell differentiation remains poorly understood. MLL2 is the main histone 3 lysine 4 (H3K4) trimethyltransferase acting at bivalent promoters in embryonic stem cells (ESCs) and is required for ESCs to differentiate into neuroectoderm. We show here that this requirement occurs during exit from naive pluripotency, days before neuroectoderm differentiation is impaired. Although MLL2 knockout has only a subtle effect on transcription during exit, reducing the expression of a few important neuroectodermal transcription factors, it substantially remodels chromatin architecture, disrupting 3D chromatin loops associated with bivalent promoters. The enzymatic activity of MLL2 is not needed for stabilising these loops or for neuroectoderm differentiation. This non-catalytic function of MLL2 in stabilising 3D chromatin loops has implications for lineage specification. Because MLL2 shares features with all four MLLs, chromatin tethering, rather than H3K4 methylation, may represent the primary function of MLL proteins during lineage commitment.

cell biology↗

bioRxiv2023

The BOD1L subunit of the mammalian SETD1A complex sustains the expression of DNA damage repair genes despite restraining H3K4 trimethylation

SETD1A is the histone 3 lysine 4 (H3K4) methyltransferase central to the mammalian version of the highly conserved eight subunit Set1 complex (Set1C) that apparently conveys H3K4 trimethylation (H3K4me3) onto all active Pol II promoters. Accordingly, the Setd1a mouse knock-out dies in early embryogenesis at the epiblast stage and mouse embryonic stem cells (ESCs) die when SETD1A is removed. We report that ESC death is accompanied by loss of expression of DNA repair genes and accumulating DNA damage. BOD1L and BOD1 are homologs of the yeast Set1C subunit, Shg1, and subunits of the mammalian SETD1A and B complexes. We show that the Shg1 homology region binds to a highly conserved central alpha-helix in SETD1A and B. Like mutagenesis of Shg1 in yeast, conditional mutagenesis of Bod1l in ESCs promoted increased H3K4 di- and tri-methylation but also, like loss of SETD1A, loss of expression of DNA repair genes, increased DNA damage and cell death. In contrast to similar losses of DNA repair gene expression, the converse changes in H3K4 methylation after loss of SETD1A or BOD1L implies that H3K4 methylation is not essential for expression of the target DNA repair genes. Because BOD1L becomes highly phosphorylated after DNA damage and acts to protect damaged replication forks, the SETD1A complex, and BOD1L in particular, are key nodes for the DNA damage repair network.

cell biology↗

bioRxiv2022

Tissue microenvironment dictates the state of human induced pluripotent stem cell-derived endothelial cells of distinct developmental origin in 3D cardiac microtissues

Each tissue and organ in the body has its own type of vasculature. Here we demonstrate that organotypic vasculature for the heart can be recreated in a three-dimensional cardiac microtissue (MT) model composed of human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes (CMs), cardiac fibroblasts (CFs) and endothelial cells (ECs). ECs in cardiac MTs upregulated expression of markers enriched in human intramyocardial ECs (iECs), such as CD36, CLDN5, APLNR, NOTCH4, IGFBP3, ARHGAP18, which were previously identified in the single-cell RNA-seq dataset from the human fetal heart (6.5-7 weeks post coitum). We further show that the local microenvironment largely dictates the organ-specific identity of hiPSC-derived ECs: we compared ECs of different developmental origins derived from two distinct mesoderm subtypes (cardiac and paraxial mesoderm) and found that independent of whether the ECs were cardiac or paraxial mesoderm derived, they acquired similar identities upon integration into cardiac microtissues. This was confirmed by single-cell RNA-seq. Overall, the results indicated that whilst the initial gene profile of ECs was dictated by developmental origin, this could be modified by the local tissue environment such that the original identity was lost and the organotypic identity acquired through local environmental signals. This developmental "plasticity" in ECs has implications for multiple pathological and disease states.

developmental biology↗

bioRxiv2020

MLL1 is required for maintenance of intestinal stem cells and the expression of the cell adhesion molecule JAML

Epigenetic control is crucial for lineage-specific gene expression that creates cellular identity during mammalian development and in adult organism. Histone 3 lysine 4 methylation (H3K4) is a universal epigenetic mark. Mixed lineage leukemia (MLL1) is the founding member of the mammalian family of H3K4 methyltransferases. It was originally discovered as the main gene mutated in early onset leukemias and then found to be required for hematopoietic stem cell development and maintenance. However, the roles of MLL1 in non-hematopoietic tissues remain largely unexplored. To bypass hematopoietic lethality, we used bone marrow transplantation and conditional mutagenesis to discover that the most overt phenotype in Mll1-mutant mice is intestinal failure. Loss of MLL1 is accompanied by a differentiation bias towards the secretory lineage with increased numbers of goblet cells. MLL1 is expressed in intestinal stem cells (ISCs) and transit amplifying (TA) cells but at reduced levels in Paneth cells and not in the villus. MLL1 is required for the maintenance of intestinal stem cells (ISCs) and proliferation in the crypt. Transcriptome analysis implicate MLL1-dependent expression in ISCs of several transcription factors including Pitx2, Gata4, Foxa1 and Onecut2, and also a cell adhesion molecule, Jaml. Reactive transcriptome changes in Paneth cells and organoids imply that JAML plays a key role in the crypt stem cell niche. All known postnatal functions of MLL1 relate to stem cell maintenance and lineage decisions thereby highlighting the suggestion that MLL1 is a master stem cell regulator. Author SummaryThe ability of adult stem cells to produce functional progenies through differentiation is critical to maintain function and integrity of organs. A fundamental challenge is to identify factors that control the transition from self-renewal to the differentiated state. Epigenetic factors amongst others can fullfill such a role. Methylation of histone 3 on lysine 4 (H3K4) is a posttranslational epigenetic modification that is associated with actively transcribed genes. In mammals, this epigenetic mark is catalyzed by one of six H3K4 methyltransferases, including the founding member of the family, MLL1. MLL1 is important for the precise functioning of the hematopoietic stem cell compartment. This raises the possibility of similar functions in other adult stem cell compartments. Due to its intense self-renewal kinetics and its simple repetitive architecture, the intestinal epithelium serves as a prime model for studying adult stem cells. We demonstrate that MLL1 controls intestinal stem cell proliferation and differentiation. Additionally, transcriptome analysis suggests a pertubation in the close interaction between intestinal stem cells and neighbouring Paneth cells through loss of junction adhesion molecule like (JAML). Our work sheds new light on the function of MLL1 for the control of intestinal stem cell identity.

genetics↗

bioRxiv2020

Reduced purine biosynthesis in humans after their divergence from Neandertals

We analyze the metabolomes of humans, chimpanzees and macaques in muscle, kidney and three different regions of the brain. Whereas several compounds in amino acid metabolism occur at either higher or lower concentrations in humans than in the other primates, metabolites in oxidative phosphorylation and purine biosynthesis are consistently present in lower concentrations in the brains of humans. In particular, metabolites downstream of adenylosuccinate lyase, which catalyzes two reactions in purine synthesis, occur at lower concentrations in humans. This enzyme carries an amino acid substitution that is present in all humans today but absent in Neandertals. By introducing the modern human substitution into the genomes of mice, as well as the ancestral, Neandertal-like substitution into the genomes of human cells, we show that this amino acid substitution is responsible for much or all of the reduction of de novo synthesis of purines in humans.

evolutionary biology↗

bioRxiv2019

MLL4 is required for the first embryonic collective cell migration whereas MLL3 is not required until birth

Methylation of histone 3 lysine 4 (H3K4) is a major epigenetic system associated with gene expression. In mammals there are six H3K4 methyltransferases related to yeast Set1 and fly Trithorax, including two orthologs of fly Trithorax-related: MLL3 and MLL4. Exome sequencing has documented high frequencies of Mll3 and Mll4 mutations in many types of human cancer. Despite this emerging importance, the requirements of these sister genes in mammalian development have only been incompletely reported. Here we examined the null phenotypes to establish that MLL3 is first required for lung maturation whereas MLL4 is first required for migration of the anterior visceral endoderm (AVE) that initiates gastrulation and is the first collective cell migration in development. This migration is preceded by a columnar to squamous transition in visceral endoderm cells that depends on MLL4. Furthermore, Mll4 mutants display incompletely penetrant, sex distorted, embryonic haploinsufficiency and adult heterozygous mutants show aspects of Kabuki syndrome, indicating that MLL4 action, unlike MLL3, is dosage dependent. The highly specific and discordant functions of these sister genes argues against their action as general enhancer factors. Summary statementThe H3K4 methyltransferases MLL3 and MLL4 have strikingly different null phenotypes during mouse development; MLL3 is required for lung maturation whereas MLL4 is required for anterior visceral endoderm migration.

developmental biology↗

bioRxiv2018

Human axial progenitors generate trunk neural crest cells

The neural crest (NC) is a multipotent embryonic cell population generating distinct cell types in an axial position-dependent manner. The production of NC cells from human pluripotent stem cells (hPSCs) is a valuable approach to study human NC biology. However, the origin of human trunk NC remains undefined and therefore current in vitro differentiation strategies induce only a modest yield of trunk NC cells. Here we show that hPSC-derived axial progenitors, the posteriorly-located drivers of embryonic axis elongation, give rise to trunk NC cells and their derivatives. Moreover, we define the molecular signatures associated with the emergence of human NC cells of distinct axial identities in vitro. Collectively, our findings indicate that there are two routes toward a human post-cranial NC state: the birth of cardiac and vagal NC is facilitated by retinoic acid-induced posteriorisation of an anterior precursor whereas trunk NC arises within a pool of posterior axial progenitors.

developmental biology↗

bioRxiv2017

Differential epigenetic landscapes and transcription factors explain X-linked gene behaviours during X-chromosome reactivation in the mouse inner cell mass

X-chromosome inactivation (XCI) is established in two waves during mouse development. First, silencing of the paternal X chromosome (Xp) is triggered, with transcriptional repression of most genes and enrichment of epigenetic marks such as H3K27me3 being achieved in all cells by the early blastocyst stage. XCI is then reversed in the inner cell mass (ICM), followed by a second wave of maternal or paternal XCI, in the embryo-proper. Although the role of Xist RNA in triggering XCI is now clear, the mechanisms underlying Xp reactivation in the inner cell mass have remained enigmatic. Here we use in vivo single cell approaches (allele-specific RNAseq, nascent RNA FISH and immunofluorescence) and find that different genes show very different timing of reactivation. We observe that the genes reactivate at different stages and that initial enrichment in H3K27me3 anti-correlates with the speed of reactivation. To define whether this repressive histone mark is lost actively or passively, we investigate embryos mutant for the X-encoded H3K27me3 demethylase, UTX. Xp genes that normally reactivate slowly are retarded in their reactivation in Utx mutants, while those that reactive rapidly are unaffected. Therefore, efficient reprogramming of some X-linked genes in the inner cell mass is very rapid, indicating minimal epigenetic memory and potentially driven by transcription factors, whereas others may require active erasure of chromatin marks such as H3K27me3.

developmental biology↗