Biology subjects

Luperchio, T. R.

Publications and source records attributed to Luperchio, T. R..

5 recordsLinked to original sources

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↗

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↗

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

The repressive genome compartment is established early in the cell cycle before forming the lamina associated domains

Three-dimensional (3D) genome organization is thought to be important for regulation of gene expression. Chromosome conformation capture-based studies have uncovered ensemble organizational principles such as active (A) and inactive (B) compartmentalization. In addition, large inactive regions of the genome associate with the nuclear lamina, the Lamina Associated Domains (LADs). Here we investigate the dynamic relationship between A/B-compartment organization and the 3D organization of LADs. Using refined algorithms to identify active (A) and inactive (B) compartments from Hi-C data and to define LADs from DamID, we confirm that the LADs correspond to the B-compartment. Using specialized chromosome conformation paints, we show that LAD and A/B-compartment organization are dependent upon chromatin state and A-type lamins. By integrating single-cell Hi-C data with live cell imaging and chromosome conformation paints, we demonstrate that self-organization of the B-compartment within a chromosome is an early event post-mitosis and occurs prior to organization of these domains to the nuclear lamina.

genomics↗

bioRxiv2017

Chromosome Conformation Paints Reveal The Role Of Lamina Association In Genome Organization And Regulation

Non-random, dynamic three-dimensional organization of the nucleus is important for regulation of gene expression. Numerous studies using chromosome conformation capture strategies have uncovered ensemble organizational principles of individual chromosomes, including organization into active (A) and inactive (B) compartments. In addition, large inactive regions of the genome appear to be associated with the nuclear lamina, the so-called Lamina Associated Domains (LADs). However, the interrelationship between overall chromosome conformation and association of domains with the nuclear lamina remains unclear. In particular, the 3D organization of LADs within the context of the entire chromosome has not been investigated. In this study, we describe \"chromosome conformation paints\" to determine the relationship in situ between LAD and non-LAD regions of the genome in single cells. We find that LADs organize into constrained and compact regions at the nuclear lamina, and these findings are supported by an integrated analysis of both DamID and Hi-C data. Using a refined algorithm to identify active (A) and inactive (B) compartments from Hi-C data, we demonstrate that the LADs correspond to the B compartment. We demonstrate that in situ single cell chromosome organization is strikingly predicted by integrating both Hi-C and DamID data into a chromosome conformation model. In addition, using the chromosome conformation paints, we demonstrate that LAD (and B-compartment) organization is dependent upon both chromatin state and Lamin A/C. Finally, we demonstrate that small regions within LADs escape the repressive regime at the peripheral zone to interact with the A-compartment and are enriched for both transcription start sites (TSSs) and active enhancers.

cell biology↗