Reduced survival of Mx1-Cre, NrasG12D mice. (A) Injecting Mx1-Cre, NrasG12D mice with poly I:C excises a transcriptional repressor (“STOP”) cassette and induces NrasG12D expression from the endogenous genetic locus. (B) The recombined NrasG12D allele is detected in blood cells 3 weeks after a single injection of poly I:C (250 μg) in mice that inherited the Mx1-Cre transgene (Mx1−Cre+) but not in Mx1−Cre− littermates. The DNA fragments amplified from the WT and recombined alleles migrate at 500 and 534 bp, respectively. (C) Kaplan-Meier survival curves of Mx1-Cre, NrasG12D (n = 22) and control WT littermates (n = 38) in the C57BL6/129Sv/jae F1 background (P < .0001).