We monitored mammary tumor formation in MMTV-NIC mice bearing only the endogenous allele of Usp22 (Usp22+/+) or bearing one (Usp22OE/+) or two (Usp22OE/OE) copies of the Usp22 OE transgene in addition to the endogenous allele (Fig 1B). The gene discussed is USP22; the disease is breast cancer.