Jones Takako I, Parilla Megan, Jones Peter L
The Department of Cell and Developmental Biology, University of Massachusetts Medical School Worcester, Massachusetts, United States of America.
The Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America.
PLoS One. 2016 Mar 4;11(3):e0150938. doi: 10.1371/journal.pone.0150938. eCollection 2016.
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.
面肩肱型肌营养不良症(FSHD)通常是一种成年起病的显性肌病。与两种形式的FSHD相关的4号染色体q35区域的表观遗传变化导致抑制作用松弛,DUX4-fl(DUX4全长)的体细胞表达增加,DUX4-fl是DUX4基因的致病性可变剪接异构体。DUX4-fl编码一种在健康睾丸和多能干细胞中表达的转录因子;然而,在FSHD中,肌源性细胞中DUX4-fl水平升高会导致靶基因的异常调控。事实证明,在体内研究DUX4-fl很困难;因此,人们对其正常和致病作用知之甚少。DUX4-fl在FSHD来源的人类肌肉和肌源性细胞中的内源性表达极低,在体细胞中DUX4-fl的外源性表达会迅速诱导细胞毒性,并且部分由于灵长类谱系以外缺乏保守性,基于DUX4-fl的可行动物模型一直难以建立。相比之下,与FSHD相关的FRG1(FSHD区域基因1)在从无脊椎动物到人类的进化过程中是保守的,并且已经在几种模式生物中进行了研究。FRG1的表达对肌肉组织和脉管系统的发育至关重要,FRG1的过表达会产生肌病表型,但FRG1的正常和病理功能尚未得到很好的理解。有趣的是,当FRG1被确定为DUX4-FL的直接转录靶点时,DUX4和FRG1最近被联系起来。为了更好地理解在FSHD中受DUX4-fl和FRG1影响的途径,我们利用UAS/GAL4二元系统的控制,生成了表达这两种基因的果蝇转基因品系。利用这些品系,我们生成了可筛选的表型,概括了DUX4-fl或FRG1过表达的某些已知后果。这些转基因果蝇品系提供了资源,用于在一种遗传上易于处理的生物体中剖析受DUX4-fl或FRG1影响的途径,并可能为FSHD的肌肉发育和致病机制提供见解。