The transgene insertion comprises the following sequences flanked by insulator sequences: the CAG promoter, a loxP site flanked STOP cassette, sequence encoding amino acids of 1744 2531 (Notch1 intracellular domain; NICD) of mouse Notch1, and poly(A) signal sequences. The Notch1 sequence is only expressed after cre-mediated removal of the STOP cassette. (J:273599)