Samples of the tumor-free back skin and DMBA/TPA-induced skin tumors from wild-type FVB/N mice were immunohistochemically (IHC) stained for Ki-67, a cell proliferation marker (Gerdes et al., 1984), and myosin regulatory light chain (MLC) phosphorylated at Ser19 site (pS19-MLC), as the pS19-MLC level reflects the contractile activity of actomyosin (Riento and Ridley, 2003) (Figure 1A), wherein smooth and skeletal muscle cells were used as the internal positive control for pS19-MLC staining (Supplementary Figures S1A,B). This evidence concerns the gene MLC1 and skin neoplasm.