Biology subjects

Tapscott, S. J.

Publications and source records attributed to Tapscott, S. J..

11 recordsLinked to original sources

bioRxiv2025

A discrete region of the D4Z4 is sufficient to initiate epigenetic silencing

The DUX4 transcription factor is briefly expressed in the early embryo and is epigenetically repressed in somatic tissues. Loss of epigenetic repression can result in the aberrant expression of DUX4 in skeletal muscle and can cause facioscapulohumeral dystrophy (FSHD). Multiple factors have been identified as necessary to maintain epigenetic silencing of DUX4 in skeletal muscle, but whether specific sequences at the DUX4 locus are sufficient for epigenetic silencing has been unknown. We cloned fragments of the D4Z4 macrosatellite repeat, the DNA region that encompasses the DUX4 retrogene, adjacent to a reporter driven by a constitutive promoter and identified a single fragment sufficient to epigenetically repress reporter gene expression. Previously identified suppressors of DUX4 expression--SETDB1, ATF7IP, SIN3A/B, and LRIF1--were necessary for silencing activity and p38 inhibitors enhanced suppression. These findings identify a key regulatory sequence for D4Z4 epigenetic repression and establish a model system for mechanistic and discovery studies.

molecular biology↗

bioRxiv2025

Multi-scale machine learning model predicts muscle and functional disease progression in FSHD

Facioscapulohumeral muscular dystrophy (FSHD) is a genetic neuromuscular disorder characterized by progressive muscle degeneration with substantial variability in severity and progression patterns. FSHD is a highly heterogeneous disease; however, current clinical metrics used tracking disease progression lack sensitivity for personalized assessment, which greatly limits the design and execution of clinical trials. This study introduces a multi-scale machine learning framework leveraging whole-body magnetic resonance imaging (MRI) and clinical data to predict regional, muscle, joint, and functional progression in FSHD. The goal this work is to create a digital twin of individual FSHD patients that can be leveraged in clinical trials. Using a combined dataset of over 100 patients from seven studies, MRI-derived metrics--including fat fraction, lean muscle volume, and fat spatial heterogeneity at baseline--were integrated with clinical and functional measures. A three-stage random forest model was developed to predict annualized changes in muscle composition and a functional outcome (timed up-and-go (TUG)). All model stages revealed strong predictive performance in separate holdout datasets. After training, the models predicted fat fraction change with a root mean square error (RMSE) of 2.16% and lean volume change with a RMSE of 8.1ml in a holdout testing dataset. Feature analysis revealed that metrics fat heterogeneity within muscle predicts muscle-level progression. The stage 3 model that combined functional muscle groups and predicted change in TUG with a RMSE of 0.6 seconds, in the holdout testing dataset. This study demonstrates the machine learning models incorporating individual muscle and performance data can effectively predict MRI disease progression and functional performance of complex tasks, addressing the heterogeneity and nonlinearity inherent in FSHD. Further studies incorporating larger longitudinal cohorts as well as comprehensive clinical and functional measures will allow for expanding and refining this model. As many neuromuscular diseases are characterized by varability and heterogeneity similar to FSHD, such approaches have broad applicability.

bioengineering↗

bioRxiv2024

DUX4-induced HSATII RNA accumulation drives protein aggregation impacting RNA processing pathways.

RNA-driven protein aggregation leads to cellular dysregulation, disrupting normal cellular processes, and contributing to the development of diseases and tumorigenesis. Here, we show that double homeobox 4 (DUX4), an early embryonic transcription factor and causative gene of facioscapulohumeral muscular dystrophy (FSHD), induces the accumulation of stable intranuclear RNAs, including nucleolar RNA and human satellite II (HSATII) RNA. Stable intranuclear RNAs drive protein aggregation in DUX4-expressing muscle cells. Specifically, HSATII RNA sequesters RNA methylation factors. HSATII-YBX1 ribonucleoprotein (RNP) complex formation is mediated by HSATII double-stranded RNA and NSUN2 activity. Aberrant HSATII-RNP complexes affect RNA processing pathways, including RNA splicing. Differential splicing of genes mediated by HSATII-RNP complexes are associated with pathways known to be dysregulated by DUX4 expression. These findings highlight the broader influence of DUX4 on nuclear RNA dynamics and suggest that HSATII RNA could be a critical mediator of RNA processing regulation. Understanding the impact of HSATII-RNP formation on RNA processing provides insight into the molecular mechanisms underlying FSHD. SUMMARYArends et al. show that DUX4-induction of stable intranuclear RNA, including pericentromeric human satellite II (HSATII) repeat RNA, leads to nuclear protein aggregation. HSATII ribonucleoprotein complexes impact RNA processing downstream of DUX4 expression.

molecular biology↗

bioRxiv2024

E-box independent chromatin recruitment turns MYOD into a transcriptional repressor

MYOD is an E-box sequence-specific basic Helix-Loop-Helix (bHLH) transcriptional activator that, when expressed in non-muscle cells, induces nuclear reprogramming toward skeletal myogenesis by promoting chromatin accessibility at previously silent loci. Here, we report on the identification of a previously unrecognized property of MYOD as repressor of gene expression, via E-box-independent chromatin binding within accessible genomic elements, which invariably leads to reduced chromatin accessibility. MYOD-mediated repression requires the integrity of functional domains previously implicated in MYOD-mediated activation of gene expression. Repression of mitogen-and growth factor-responsive genes occurs through promoter binding and requires a highly conserved domain within the first helix. Repression of cell-of-origin/alternative lineage genes occurs via binding and decommissioning of distal regulatory elements, such as super-enhancers (SE), which requires the N-terminal activation domain as well as two chromatin-remodeling domains and leads to reduced strength of CTCF-mediated chromatin interactions. Surprisingly, MYOD-mediated chromatin compaction and repression of transcription do not associate with reduction of H3K27ac, the conventional histone mark of enhancer or promoter activation, but with reduced levels of the recently discovered histone H4 acetyl-methyl lysine modification (Kacme). These results extend MYOD biological properties beyond the current dogma that restricts MYOD function to a monotone transcriptional activator and reveal a previously unrecognized functional versatility arising from an alternative chromatin recruitment through E-box or non-E-box sequences. The E-box independent repression of gene expression by MYOD might provide a promiscuous mechanism to reduce chromatin accessibility and repress cell-of-origin/alternative lineage and growth factor/mitogen-responsive genes to safeguard the integrity of cell identity during muscle progenitor commitment toward the myogenic lineage.

molecular biology↗

bioRxiv2024

SUMOylation differentially regulates SMCHD1 complex formation and function in a genomic context-specific manner

Structural Maintenance of Chromosomes Hinge Domain Containing 1 (SMCHD1) is a chromatin repressor regulating gene expression and chromatin architecture of distinct autosomal and X-chromosomal loci. SMCHD1 mutations cause derepression of the D4Z4 macrosatellite repeat-embedded DUX4 gene in skeletal muscle of facioscapulohumeral muscular dystrophy (FSHD) patients Little is known about the regulation and post-translational modification of SMCHD1. Here we report the SUMOylation dynamics of SMCHD1 and its impact on autosomal single copy and repetitive loci, and the inactive X chromosome (Xi). We identify that SMCHD1 is SUMOylated primarily at lysine 1374, uncover factors regulating SMCHD1 SUMOylation, and demonstrate that SMCHD1 interacts with chromatin repressors TRIM28, HNRNPK and SETDB1 in a SUMO-dependent manner. We find that SUMOylation impacts Xi engagement of SMCHD1, maintenance of a repressive D4Z4 chromatin structure preventing DUX4 expression, and regulation of LRIF1 promoter activity. The rapid, SUMO-dependent upregulation of DUX4 could explain the bursts of DUX4 expression typical for FSHD muscle.

molecular biology↗

bioRxiv2024

Suspended Tissue Open Microfluidic Patterning (STOMP)

Free-standing tissue structures tethered between pillars are powerful mechanobiology tools for studying cell contraction. To model interfaces ubiquitous in natural tissues and upgrade existing single-region suspended constructs, we developed Suspended Tissue Open Microfluidic Patterning (STOMP), a method to create multi-regional suspended tissues. STOMP uses open microfluidics and capillary pinning to pattern subregions within free-standing tissues, facilitating the study of complex tissue interfaces, such as diseased-healthy boundaries (e.g., fibrotic-healthy) and tissue-type interfaces (e.g., bone-ligament). We observed altered contractile dynamics in fibrotic-healthy engineered heart tissues compared to single-region tissues and differing contractility in bone-ligament enthesis constructs compared to single-tissue periodontal ligament models. STOMP is a versatile platform - surface tension-driven patterning removes material requirements common with other patterning methods (e.g., shear-thinning, photopolymerizable) allowing tissue generation in multiple geometries with native extracellular matrices and advanced 4D materials. STOMP combines the contractile functionality of suspended tissues with precise patterning, enabling dynamic and spatially controlled studies.

bioengineering↗

bioRxiv2023

Validation of the association between MRI and gene signatures in facioscapulohumeral dystrophy muscle: implications for clinical trial design

Identifying the aberrant expression of DUX4 in skeletal muscle as the cause of facioscapulohumeral dystrophy (FSHD) has led to rational therapeutic development and clinical trials. Several studies support the use of MRI characteristics and the expression of DUX4-regulated genes in muscle biopsies as biomarkers of FSHD disease activity and progression, but reproducibility across studies needs further validation. We performed lower-extremity MRI and muscle biopsies in the mid-portion of the tibialis anterior (TA) muscles bilaterally in FSHD subjects and validated our prior reports of the strong association between MRI characteristics and expression of genes regulated by DUX4 and other gene categories associated with FSHD disease activity. We further show that measurements of normalized fat content in the entire TA muscle strongly predict molecular signatures in the mid-portion of the TA. Together with moderate-to-strong correlations of gene signatures and MRI characteristics between the TA muscles bilaterally, these results suggest a whole muscle model of disease progression and provide a strong basis for inclusion of MRI and molecular biomarkers in clinical trial design.

molecular biology↗

bioRxiv2022

Human DUX4 and mouse Dux interact with STAT1 and broadly inhibit interferon-stimulated gene induction

DUX4 activates the first wave of zygotic gene expression in the early embryo. Mis-expression of DUX4 in skeletal muscle causes facioscapulohumeral dystrophy (FSHD), whereas expression in cancers suppresses IFN{gamma}-induction of MHC Class I and contributes to immune evasion. We show that the DUX4 protein interacts with STAT1 and broadly suppresses expression of IFN{gamma} stimulated genes by decreasing bound STAT1 and Pol-II recruitment. Transcriptional suppression of ISGs requires conserved (L)LxxL(L) motifs in the carboxyterminal region of DUX4 and phosphorylation of STAT1 Y701 enhances interaction with DUX4. Consistent with these findings, expression of endogenous DUX4 in FSHD muscle cells and the CIC-DUX4 fusion containing the DUX4 CTD in a sarcoma cell line inhibit IFN{gamma}-induction of ISGs. Mouse Dux similarly interacted with STAT1 and suppressed IFN{gamma} induction of ISGs. These findings identify an evolved role of the DUXC family in modulating immune signaling pathways with implications for development, cancers, and FSHD.

developmental biology↗

bioRxiv2020

Evolutionarily conserved regulation of embryonic fast-twitch skeletal muscle differentiation by Pbx factors

Vertebrate skeletal muscles are composed of both slow-twitch and fast-twitch fiber types. How the differentiation of distinct fiber types is activated during embryogenesis is not well characterized. Skeletal muscle differentiation is initiated by the activity of the myogenic basic helix-loop-helix (bHLH) transcription factors Myf5, Myod1, Myf6, and Myog. Myod1 functions as a muscle master regulatory factor and directly activates muscle differentiation genes, including those specific to both slow and fast muscle fibers. Our previous studies showed that Pbx TALE-class homeodomain proteins bind with Myod1 on the promoter of the zebrafish fast muscle gene mylpfa and are required for proper activation of mylpfa expression and the fast-twitch muscle-specific differentiation program in zebrafish embryos. Pbx proteins have also been shown to bind regulatory regions of muscle differentiation genes in mammalian muscle cells in culture. Here, we use new zebrafish mutant strains to confirm the essential roles of zebrafish Pbx factors in embryonic fast muscle differentiation. Furthermore, we examine the requirements for Pbx genes in mouse embryonic skeletal muscle differentiation, an area that has not been investigated in the mammalian embryo. Removing Pbx1 function from skeletal muscle in Myf5Cre/+;Pbx1fl/fl mouse embryos has minor effects on embryonic muscle development. However, concomitantly deleting Pbx2 function in Myf5Cre/+;Pbx1fl/fl;Pbx2-/- mouse embryos causes delayed activation and reduced expression of fast muscle differentiation genes. In the mouse, Pbx1/Pbx2-dependent fast muscle genes closely match those that have been previously shown to be dependent on murine Six1 and Six4. This work establishes evolutionarily conserved requirements for Pbx factors in embryonic fast muscle differentiation. Our studies are revealing how Pbx homeodomain proteins help direct specific cellular differentiation pathways.

developmental biology↗

bioRxiv2019

DUX4-induced bidirectional HSATII satellite repeat transcripts form intranuclear double stranded RNA foci in human cell models of FSHD

The DUX4 transcription factor is normally expressed in the cleavage stage embryo and regulates genes involved in embryonic genome activation. Mis-expression of DUX4 in skeletal muscle, however, is toxic and causes facioscapulohumeral muscular dystrophy (FSHD). We recently showed DUX4-induced toxicity is due, in part, to the activation of the double-stranded RNA (dsRNA) response pathway and the accumulation of intranuclear dsRNA foci. Here, we determined the composition of DUX4-induced dsRNAs. We found that a subset of DUX4-induced dsRNAs originate from inverted Alu repeats embedded within the introns of DUX4-induced transcripts and from DUX4-induced dsRNA-forming intergenic transcripts enriched for endogenous retroviruses, Alu and LINE-1 elements. However, these repeat classes were also represented in dsRNAs from cells not expressing DUX4. In contrast, pericentric human satellite II (HSATII) repeats formed a class of dsRNA specific to the DUX4 expressing cells. Further investigation revealed that DUX4 can initiate the bidirectional transcription of normally heterochromatin-silenced HSATII repeats. DUX4 induced HSATII RNAs co-localized with DUX4-induced nuclear dsRNA foci and with intranuclear aggregation of EIF4A3 and ADAR1. Finally, gapmer-mediated knockdown of HSATII transcripts depleted DUX4-induced intranuclear ribonucleoprotein aggregates and decreased DUX4-induced cell death, suggesting that HSATII formed dsRNAs contribute to DUX4 toxicity.

molecular biology↗

bioRxiv2018

Quantitative proteomics reveals key roles for post-transcriptional gene regulation in the molecular pathology of FSHD

DUX4 is a transcription factor whose misexpression in skeletal muscle causes facioscapulohumeral muscular dystrophy (FSHD). While DUX4s transcriptional activity has been extensively characterized, the DUX4-induced proteome remains undescribed. Here, we report concurrent measurement of RNA and protein levels in DUX4-expressing cells via RNA-seq and quantitative mass spectrometry. DUX4 transcriptional targets were robustly translated, confirming the likely clinical relevance of proposed FSHD biomarkers. However, a multitude of mRNAs and proteins exhibited discordant expression changes upon DUX4 expression. Our dataset revealed unexpected proteomic, but not transcriptomic, dysregulation of diverse molecular pathways, including Golgi apparatus fragmentation, as well as extensive post-transcriptional buffering of stress response genes. Key components of RNA degradation machineries, including UPF1, UPF3B, and XRN1, exhibited suppressed protein, but not mRNA, levels, explaining the build-up of aberrant RNAs that characterizes DUX4-expressing cells. Our results provide a resource for the FSHD community and illustrate the importance of post-transcriptional processes to DUX4-induced pathology.

genomics↗