Double homeobox 4 (DUX4) is a candidate disease gene for facioscapulohumeral 
dystrophy (FSHD), one of the most common muscular dystrophies characterized by 
progressive skeletal muscle degeneration. Despite great strides in understanding 
precise genetics of FSHD, the molecular pathophysiology of the disease remains 
unclear. One of the major limitations has been the availability of appropriate 
molecular tools to study DUX4 protein. In the present study, we report the 
development of five new monoclonal antibodies targeted against the N- and 
C-termini of human DUX4, and characterize their reactivity using Western blot 
and immunofluorescence staining. Additionally, we show that expression of the 
canonical full coding DUX4 induces cell death in human primary muscle cells, 
whereas the expression of a shorter splice form of DUX4 results in no such 
toxicity. Immunostaining with these new antibodies reveals a differential effect 
of two DUX4 isoforms on human muscle cells. These antibodies will provide an 
excellent tool for investigating the role of DUX4 in FSHD pathogenesis.