NOTCH1 and neoplasm: Notch1 has been shown to function as a tumor suppressor in mouse skin [31] and Pofut1/Tgfb3-Cre mice displayed isthmus hyperplasia, suggesting that the DNA damage signal seen in Pofut1/Tgfb3-Cre hair follicles was induced by aberrant cell proliferation, as found in the case of oncogene-induced DNA damage checkpoint responses [32].