Exon 6 was disrupted by an IRES-lacZ reporter and floxed neo cassette that replaced sequence encoding Met119 through the end of the gene, including the RGD region. Mutant calvarial cells showed no wild-type mRNA in either Northern blot or RT-PCR. Immunostaining of osteocytes confirmed lack of wild-type protein in mutant mice, and X-gal staining demonstrated lacZ activity in heterozygote hypertrophic chondrocytes, osteoblasts and osteocytes. (J:85859)