(A) Stacked bar graphs showing distribution of hyperplastic and dysplastic, in transition and normal-like structures before and 14 days after TAg downregulation in submandibular salivary glands of 4-month-old Tet-op-TAgMMTV-tTA/p53−/− (tTa/TAg/p53+/−) mice. (B) Bar graphs comparing relative protein expression levels in submandibular salivary tissue 14 days after TAg downregulation in 4-month-old Tet-op-TAgMMTV-tTA/p53−/− and Tet-op-TAgMMTV-tTA (tTA/TAg) and 7-month-old Tet-op-TAgMMTV-tTA mice. Absence of p53 was associated with significant reductions in relative expression levels of p21 (p<0.01), p27 (p<0.01) and total pRb (p<0.05). No significant differences in expression levels of Cyclin D1, CDK6, CDK4, Cyclin E, CDK2, phosphorylated pRb, DP-1 or E2F-1 were found between 4-month-old Tet-op-TAgMMTV-tTA/p53−/− and Tet-op-TAgMMTV-tTA mice. There were significant differences in expression of Cyclin D1, CDK6, CDK4, CDK2, pRb, phosphorylated pRb, DP-1 and E2F-1 between 7-month-old Tet-op-TAgMMTV-tTA and 4-month-old Tet-op-TAgMMTV-tTA/p53−/− and Tet-op-TAgMMTV-tTA mice. Relative protein expression levels determined by quantification of western blots using densitometry. Mean and SEM indicated. Timepoints=0 (A) and 14 (A,B) days after administration of doxycycline to downregulate TAg. m= age in months. *:p<0.05, Student’s t test (two-tailed).Cohort sizes by genotype at different timepoints: (A) 4m tTA/TAg/p53−/−: 0(n=5), 14(n=4), (B) 4m tTA/TAg/p53−/− : 14(n=3), 4m tTA/TAg: 14(n=5), 7mtTA/TAg: 14(n=5).