DUX4 and facioscapulohumeral muscular dystrophy: Given that DUX4 expression is difficult to detect in FSHD muscle cells, we employed our transgenesis system to generate a seamless vector comprising of a cassette harbouring a DUX4-responsive artificial promoter with 16 DUX4 binding sites upstream of a reporter gene (mNeon/fluorescent protein) and a downstream antibiotic selection cassette (PuroR driven by the PGK promoter: Fig. 5b).