Transgenic mice carrying the lacZ gene driven by the Fog2 promoter have been developed by S. Tevosian. In these animals, the lacZ gene is incorporated (“knocked-in”) into the Fog2 locus to allow β-galactosidase expression as a fusion protein in frame with the first 235 amino acids of the FOG2 protein. The Fog2-lacZ module is followed by an ires-eGFP cassette. This creates a null allele of Fog2 gene. The Fog2-LacZ-eGFP construct was linearized with KspI and electroporated into the CJ7 ES cells. The correctly targeted clone was selected by the Southern blot analysis and injected into C57BL/6J blastocysts. Fog2-lacZ-eGFP animals were maintained on the mixed C57BL/6J/129 background. lacZ Expression in whole dissected embryonic lungs was analyzed by staining for β-galactosidase activity with X-gal after fixation for 30 min.