p21, ccng1, foxo3b, and fbxw7 contribute to p53-dependent cell cycle arrest.

p53 is a transcription factor and important tumor suppressor gene, yet its mechanism of tumor suppression remains unclear. While PUMA/BBC3, NOXA/PMAIP1, and p21/CDKN1A regulate apoptosis and cell-cycle arrest, zebrafish lacking puma, noxa, and p21 do not develop cancer, suggesting additional p53 targets contribute to tumor suppression. We show that p53 can still induce cell-cycle arrest in the absence of p21, either following DNA damage or mdm2 loss, implicating other transcriptional target in p53-dependent cell-cycle arrest. We conducted a cross-species analysis to identify 137 conserved p53-upregulated genes. Our analysis also stresses the importance of ortholog to paralog analysis across species, since in many cases the paralog but not ortholog in differing species is p53 dependent. Using a CRISPR-Cas9 G0 "crispant" screen in mdm2, puma, noxa, and p21 quadruple knockout zebrafish, we identified ccng1, fbxw7, and foxo3b that are involved in p53-dependent cell-cycle arrest.