A GFPCre expression cassette was inserted into the transcription start site (ATG) of the Prox1 genomic locus along with a neomycin selection cassette. A thymidine kinase negative-selection cassette was also included. The targeting construct was electroporated into W9.5 mouse ES cells. Following selection and screening via standard methods, correctly targeted ES cell clones were used to generate the chimeric mice. (J:158959)