Difference of osteopontin gene regulation between bone and kidney

Osteopontin is a sialoprotein that is expressed in various cells. It plays a variety of important roles in cell adhesion, migration, signaling, calcification, and immunity. Its diverse functions indicate that the regulation of osteopontin may also vary extensively among tissues. Although osteopontin promoter has been studied in vitro, in vivo analyses may be more appropriate for elucidating osteopontin's functions. In an attempt to investigate osteopontin gene expression, we generated transgenic mice in which the bacterial beta-galactosidase reporter gene was conjugated downstream of osteopontin promoter. The osteopontin promoter was a mouse -910 bp upstream fragment, which we had previously found functional in 3T3 cells. Among 34 transgenic founders, 13 mice were transgenic, as determined with the polymerase chain reaction. Osteopontin and beta-galactosidase signals were evaluated with in situ hybridization. Among the 13 transgenic mice, 3 were beta-galactosidase-positive. In these transgenic mice, osteopontin signals were observed in bones and kidneys, whereas beta-galactosidase message was detected only in bones. This suggests that the -910 bp osteopontin promoter is active in bones but not in kidneys. These data imply that the promoter region required for osteopontin expression in kidneys may differ from that in bones.