Restricted and coordinated expression of β3-integrin and bone sialoprotein during cultured osteoblast differentiation

In this study, the expression of β3-integrin was examined in relationship to the restricted expression of bone sialoprotein (BSP). Immunohistochemical analysis indicated that the αvβ3-integrin was coincident and proximal to BSP expression in the fetal mandible bovine osteoblast culture model. αvβ3-integrin expression was expressed predominantly in a region proximal to, but not including, the substrate adherent cells. In comparison, the α5β1-integrin was expressed in a generalized pattern throughout the culture layers in a coordinated fashion to fibronectin. The temporal expression of β1- and β3-integrin was evaluated using RT-PCR and southern blot analysis. Unlike the generalized expression of β1-integrin, β3-integrin was restricted to days 3 and 5 of the culture period. The previous demonstration of similar restriction of BSP expression and the present colocalization of BSP suggests the potential coordinated expression of a specific extracellular matrix ligand with a select integrin. β3-integrin/BSP adhesion-mediated signaling may play a significant role in the process of osteoblast morphodifferentiation.