A portion of exon 1 including the ATG start site was replaced with a cassette containing an IRES element, a tau-GFP fusion gene, a loxP site, a PGK-1 promoter, a neomycin resitance gene, a PGK-1 polyA tail and a second loxP site. Western blot analysis confirmed the absence of protein in spinal cords from homozygous null mice. The tau-GFP fusion protein is expressed from the Robo3 promoter. (J:89438)