EXPRESSION OF RAT BONE SIALOPROTEIN PROMOTER IN TRANSGENIC MICE

Bone sialoprotein (BSP) is a major protein of the mineralized bone ext racellular matrix that has been implicated in the nucleation of hydrox yapatite crystals, Our previous studies have demonstrated that BSP mRN A is expressed by differentiated osteoblasts, odontoblasts, and cement oblasts involved in de novo mineralized tissue formation in a tissue-s pecific and developmentally regulated manner, To determine the basis o f the selective expression of the BSP gene, we have generated four tra nsgenic mouse lines in which similar to 2.7 kb of the rat BSP promoter ligated to a luciferase reporter gene has been stably integrated into the mouse genome, Assays of luciferase activities in 5-day-old animal s has revealed consistently high levels in bone tissues with negligibl e activities in various other organs including kidney, liver, stomach, intestine, and spleen, In some animals, variable expression was obser ved in brain and skin, Temporal analyses revealed the highest lucifera se expression in neonatal bones, with expression decreasing markedly w ith subsequent growth and development, as observed previously for the endogenous gene in rats, Immunohistochemical analysis of luciferase ac tivity and in situ hybridization of luciferase mRNA in bone tissues sh ow that differentiated osteoblasts express the highest levels of lucif erase, consistent with the induction of endogenous gene expression, Th ese studies demonstrate that the regulation of the BSP gene during ost eoblastic differentiation, together with its tissue-specific, developm entally regulated expression, is primarily mediated within the similar to 2.7 kb region of the promoter.