We asked whether USP21 regulates the stability of Gli1 and turned to CRISPR-CAS9 technology to knockout USP21 in HEK293T cells, which, like many cancer cells, show autonomous expression of Gli1 (Fig. S3A) (Dahmane et al., 1997; Kinzler et al., 1987; Mazza et al., 2013; Nolan-Stevaux et al., 2009; Tariki et al., 2014). The gene discussed is USP21; the disease is cancer.