The targeting strategy involved deleting the signal sequence and fusing a tau-lacZ PGK-neomycin cassette in frame with the initiation codon. There was no expression of endogenous mRNA by in situ hybridization in homozygous mutant animals. Heterozygous embryos expressed beta-galactosidase in a pattern that was indistinguishable from the endogenous expression pattern. (J:75288)