Consistent with its MCC-specific expression, we demonstrated that a genomic fragment within the human CCNA1 promoter can drive Luciferase reporter gene expression in response to the MCC TFs E2F4 (but only in the presence of MCIDAS), FOXJ1 and MYB (Figure 5D and Figure 5—figure supplement 1C) in 293T/17 cells, similar to a FOXJ1 promoter fragment previously shown to display MCC-restricted expression (Tan et al., 2013). Here, E2F4 is linked to Merkel cell skin cancer.