ResearchPad - facioscapulohumeral-muscular-dystrophy https://www.researchpad.co Default RSS Feed en-us © 2020 Newgen KnowledgeWorks <![CDATA[Single-nucleus RNA-seq identifies divergent populations of FSHD2 myotube nuclei]]> https://www.researchpad.co/article/elastic_article_14649 Although misexpression of DUX4 has been known as the major cause in FSHD, it is lowly expressed in patient samples and analysis of the consequences of DUX4 expression has largely relied on artificial overexpression. Here, we took advantage of recent methodological advances to observe native DUX4 expression at the single-nucleus level in FSHD2 patient-derived myotubes. Using single-nucleus RNA-seq (snRNA-seq), we were able to detect endogenous DUX4-expressing nuclei and the extent of spreading of DUX4-target gene expression across many nuclei. Our highly sensitive snRNA-seq method further allowed us to identify two populations of FSHD myotube nuclei with distinct transcriptional profiles. One is highly enriched with DUX4 and target genes (FSHD-Hi) while the other has sparser DUX4 and FSHD-induced genes expressed (FSHD-Lo), reflecting two potentially different pathological states of patient myotubes. We observed a set of transcription factors specifically upregulated in FSHD-Hi myotube nuclei associated with the cell cycle, and significant upregulation of DUX4 paralog DUXA that contributes to further upregulation of DUX4 target genes. We propose that transcription factors downstream of DUX4 may amplify DUX4 signal and thus act to perpetuate FSHD.

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<![CDATA[Transgenic Drosophila for Investigating DUX4 and FRG1, Two Genes Associated with Facioscapulohumeral Muscular Dystrophy (FSHD)]]> https://www.researchpad.co/article/5989db4bab0ee8fa60bda2e6

Facioscapulohumeral muscular dystrophy (FSHD) is typically an adult onset dominant myopathy. Epigenetic changes in the chromosome 4q35 region linked to both forms of FSHD lead to a relaxation of repression and increased somatic expression of DUX4-fl (DUX4-full length), the pathogenic alternative splicing isoform of the DUX4 gene. DUX4-fl encodes a transcription factor expressed in healthy testis and pluripotent stem cells; however, in FSHD, increased levels of DUX4-fl in myogenic cells lead to aberrant regulation of target genes. DUX4-fl has proven difficult to study in vivo; thus, little is known about its normal and pathogenic roles. The endogenous expression of DUX4-fl in FSHD-derived human muscle and myogenic cells is extremely low, exogenous expression of DUX4-fl in somatic cells rapidly induces cytotoxicity, and, due in part to the lack of conservation beyond primate lineages, viable animal models based on DUX4-fl have been difficult to generate. By contrast, the FRG1 (FSHD region gene 1), which is linked to FSHD, is evolutionarily conserved from invertebrates to humans, and has been studied in several model organisms. FRG1 expression is critical for the development of musculature and vasculature, and overexpression of FRG1 produces a myopathic phenotype, yet the normal and pathological functions of FRG1 are not well understood. Interestingly, DUX4 and FRG1 were recently linked when the latter was identified as a direct transcriptional target of DUX4-FL. To better understand the pathways affected in FSHD by DUX4-fl and FRG1, we generated transgenic lines of Drosophila expressing either gene under control of the UAS/GAL4 binary system. Utilizing these lines, we generated screenable phenotypes recapitulating certain known consequences of DUX4-fl or FRG1 overexpression. These transgenic Drosophila lines provide resources to dissect the pathways affected by DUX4-fl or FRG1 in a genetically tractable organism and may provide insight into both muscle development and pathogenic mechanisms in FSHD.

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<![CDATA[High Frequency Hearing Loss and Hyperactivity in DUX4 Transgenic Mice]]> https://www.researchpad.co/article/5989da8aab0ee8fa60b9db85

Facioscapulohumeral muscular dystrophy (FSHD) is caused by mutations leading to ectopic expression of the transcription factor DUX4, and encompasses both muscle-related and non-muscle phenotypes. Mouse models bearing this gene represent valuable tools to investigate which pathologies are due to DUX4 expression, and how DUX4 leads to these pathologies. The iDUX4(2.7) mouse contains an X-linked doxycycline-inducible DUX4 gene that shows low level basal expression in the absence of doxycycline, leading to male lethality, generally in embryo, but always before 8 weeks of age. Here, we describe additional non-muscle phenotypes in this animal model. We find that iDUX4(2.7) female carriers are extremely hyperactive, spending large amounts of time ambulating and much less time resting. Rare 3-week old males, although hypophagic, runted and extremely fragile, are capable of high activity, but show periods of catatonic torpor in which animals appear dead and respiration is virtually absent. We also examine a non-muscle phenotype of interest to FSHD, high frequency hearing loss. We find that young iDUX4(2.7) females are significantly impaired in their ability to hear at frequencies above 8 kHz. These phenotypes make the iDUX4(2.7) mouse an attractive model in which to study non-muscle activities of DUX4.

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