SIRT1 and breast cancer: We introduced the MMTV-PyMT transgene into stocks of mice carrying the H355Y point mutation [38] in the Sirt1 gene (an allele referred to as Sirt1Y that encodes a protein with no detectable catalytic activity) and studied the emergence of mammary tumors in Sirt1+/+, Sirt1+/Y, and Sirt1Y/Y females.