CDKN1A and Werner syndrome: To investigate the role of p21 or p16 in the aging process of WS, we crossed the WS mice with p21–/– or p16–/– mice and obtained the first generation (G1) triple knockout mice mTer–/–Wrn–/–p21–/– (p21-TKO) or mTer–/–Wrn–/–p16–/– (p16-TKO).