Dear Editor,CRISPR/Cas9 has revolutionized genome editing technology due to its simplicity and robustness (Mali et al.,2013).Several inducible CRISPR/Cas9 systems recently developed make spatiotemporal genome editing possible (Konermann et al.,2013;Balboa et al.,2015;Dow et al.,2015;Zetsche et al.,2015;Liu et al.,2016;Kleinjan et al.,2017;Maji et al.,2017;Senturk et al.,2017;Lu et al.,2018).However,whether these inducible CRISPR/Cas9 systems can mediate efficient in vivo somatic mutagenesis for tumor modeling remains to be tested.Destabilizing domain (DD),a member of the post-translationally inducible elements,can be fused to Cas9 protein to construct an inducible CRISPR/Cas9 system (Senturk et al.,2017).The DD tag guides newly synthesized DD-Cas9 protein to the proteasome for degradation,which can be abrogated by ligand trimethoprim (TMP) (Fig.1A) (lwamoto et al.,2010;Sando et al.,2013).Because of the convenience of TMP delivery and no endogenous targets found for TMP in mammals,TMP-inducible Cas9 stabilization would be extremely attractive for achieving post-translationally tunable genome editing in vivo.