CDKN1A and neoplasm: A more focused shRNA screen of known targets of Trp53 was conducted using fetal liver HSCs of mice that were either Eμ-Myc Puma-/- or Cdkn1a(p21)-/-Puma-/- in order to identify targets of p53 that were responsible for its tumor suppressor role independently of Cdkn1a or Puma (184).