RB1 and neoplasm: Consistent with the loss of Rb1 in TEAZ tumors, when we stained for phospho-Rb1 in both a TEAZ tumor and standard embryo injection F0 tumor (i.e. mitfa:BRAF injected into a tp53−/− background without any Cas9/sgRNA), we found that most of the cells in the TEAZ tumor are phospho-Rb1 negative, whereas most of the embryo injection tumor cells are Rb1+ (Fig. S3).