EZH2 and neoplasm: Interestingly, Ezh2-deficient tumours assessed for H3K27me3 by immunofluorescence at endpoint exhibited undetectable levels of H3K27me3 in the tumour epithelium, indicating that Ezh1 was not able to compensate for the loss of Ezh2 histone methyltransferase activity (Fig. 1c, Supplementary Figure 1C, D).