Testing the effects of FSHD candidate gene expression in vertebrate muscle development.
The genetic lesion leading to facioscapulohumeral muscular dystrophy (FSHD) is a dominant deletion at the 4q35 locus. The generally accepted disease model involves an epigenetic dysregulation in the region resulting in the upregulation of one or more proximal genes whose overexpression specifically affects skeletal muscle. However, multiple FSHD candidate genes have been proposed without clear consensus. Using Xenopus laevis as a model for vertebrate development our lab has studied the effects of overexpression of the FSHD candidate gene ortholog, frg1 (FSHD region gene 1), showing that increased levels of frg1 systemically led specifically to an abnormal musculature and increased angiogenesis, the two most prominent clinical features of FSHD. Here we studied the overexpression effects of three other promising FSHD candidate genes, DUX4, DUX4c, and PITX1 using the same model system and methods for direct comparison. Expression of even very low levels of either DUX4 or pitx1 early in development led to massive cellular loss and severely abnormal development. These abnormalities were not muscle specific. In contrast, elevated levels of DUX4c resulted in no detectable adverse affects on muscle and DUX4c levels did not alter the expression of myogenic regulators. This data supports a model for DUX4 and PITX1 in FSHD only as pro-apoptotic factors if their expression in FSHD is confined to cells within the myogenic pathway; neither could account for the vascular pathology prevalent in FSHD. Taken together, increased frg1 expression alone leads to a phenotype that most closely resembles the pathophysiology observed in FSHD patients.
Wuebbles
Ryan D
RD
Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, B107 Chemical and Life Sciences Laboratory, Urbana, IL 61801, USA.
Long
Steven W
SW
Hanel
Meredith L
ML
Jones
Peter L
PL
D000818:Animals; D017209:Apoptosis / Q000502:physiology; D002454:Cell Differentiation; D015870:Gene Expression; D020869:Gene Expression Profiling; D018398:Homeodomain Proteins / Q000096:biosynthesis / Q000235:genetics*; D006801:Humans; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D020287:In Situ Nick-End Labeling; D024510:Muscle Development / Q000235:genetics*; D018482:Muscle, Skeletal / Q000166:cytology / Q000196:embryology*; D009132:Muscles; D020391:Muscular Dystrophy, Facioscapulohumeral / Q000235:genetics* / Q000378:metabolism; D051761:Paired Box Transcription Factors / Q000235:genetics* / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D029867:Xenopus Proteins / Q000235:genetics / Q000378:metabolism; D014982:Xenopus laevis
C121257:DUX4L1 protein, human; C543102:FRG1 protein, Xenopus; D018398:Homeodomain Proteins; D051761:Paired Box Transcription Factors; D029867:Xenopus Proteins; C101485:homeobox protein PITX1