We crossed mice constitutively deficient for macroH2A histones (H2afy and H2afy2 dKO strain)10 to the BrafCAPtenflTyr-CreERT2 triallelic melanoma strain22 (Extended Data Fig. 1a) and initiated tumours through the topical application of 4-hydroxytamoxifen in wild-type (WT) mice and in dKO mice. Here, MACROH2A1 is linked to neoplasm.