RFX3 and Merkel cell skin cancer: Thirdly, a gene regulatory network (GRN) associated with MCC differentiation is strongly upregulated in MEFs expressing Multicilin/E2f4VP16, including Tp73 (203 fold)24, Foxj1 (112 fold)25, Foxn4 (66-fold)23, Myb (77-fold)47,48, and the RFX family members (Rfx2; 27-fold, Rfx3; 10-fold)25 (Table S1).