SIX1 and Wilms tumor: Given the availability of robust antibodies against established podocyte markers MAFB (transcription factor) and PODXL (cell surface protein) (Tran et al., 2019), both of which were found to be expressed in all tumors within the RNA-seq dataset (Table S1), we assessed the presence and localization of these markers in addition to SIX1 and WNT5A by immunofluorescence in Wilms tumor tissue of mixed histology and unknown mutational status.