While a previous report indicated that shRNA (short hairpin RNA) overexpression could cause cytotoxicity and lethality in mice through saturation of exportin-5 and Ago2, the PMIS mice show no toxicity.48 The PMIS-miR-17-18, PMIS-miR-19-92 and PMIS-miR-200a mice do not develop cancer or die due to liver toxicity or toxicity problems. Here, XPO5 is linked to cancer.