SRC and neoplasm: Moreover, we verified that heterochromatin levels, based on expression of heterochromatin markers HP1a and H3K9me2, increased by 120% and 23%, respectively, and specifically in Ras/Src tumor cells overexpressing HP1a, i.e., tumor clones of rasG12V, HP1a; csk−/− flies, but not in surrounding non-tumor cells (Fig. 1D–G).