A cassette containing a splice acceptor, the puromycin resistance gene, and a poly A sequence was placed in front of a CAGGS promoter. Downstream of the promoter was placed a floxed terminator element containing three SV40 poly A sequences (tpA) followed by a bicistronic cassette encoding for Wnt7a and IRES-nlacZ. In the absence of Cre recombinase, transcription from the CAGGS enhancer/promoter is terminated by the tpA element. In the presence of cre recombinase, the tpA is recombined out and the CAGGS enhancer/promoter drives expression of both Wnt7a and betagalactosidase. Ectopic Wnt7a and lacZ expression were detected in the neuroepithelium of developing embryos when this allele was on a Tg(Nes-cre)1Kln transgenic background. (J:142352)