KRAS and keratoconus: However, in KC and KPC mouse models, Cre recombinase is induced at embryonic day 8.5, which leads to activation of Kras or inactivation of Trp53 (Dey et al., 2014; Hingorani et al., 2003; Hingorani et al., 2005; Rachagani et al., 2012 b).