When homozygous for both co-injected transgenes, Wnt-1/GAL4/cre-11 transgenic mice are viable and fertile. Of note for Wnt-1/GAL4/cre-11 transgenic mice on the original mixed genetic background, the donating investigator (Dr. Epstein) reported that homozygous mice may be lethal as some offspring from transgenic parents die around two months of age. Both Cre recombinase and the GAL4 transcriptional activator are expressed under the direction of wingless-related MMTV integration site 1 (Wnt1) promoter/regulatory sequences. Cre recombinase activity is detected in the Wnt1 pattern of expression: in the midbrain by 8.5 dpc and, after neural tube closure, in the dorsal and ventral midlines of the midbrain a+C78. The Jackson Laboratory 2024, used with permission.