A PGK neomycin resistance cassette replaced exons 4-7 of the Spp1 gene. No Spp1 transcript was detected by RT-PCR in embryonic fibroblasts or adult kidney from homozygous mutant animals. Spp1 transcript was not detected in homozygous mutant animals by in situ hybridization. Immunohistochemistry studies of adult kidney and bone did not detect protein in homozygous mutant mice.