TP53 and neoplasm: To that end, we first back-crossed the Shmt1 knockout mouse for 10 generations to the C57BL/6 strain and then the interbred it with 3 different tumor models where Myc is either the direct cause of transformation (λ-Myc transgenic mice, Figure 2A, [24]) or constitutes an important circuit (p53 knockout mice, Figure 2B, [27] and ApcMin mice of intestinal tumorigenesis, Figure 2C, [28]).