Thy-1 antigen expression by cells in the osteoblast lineage

Identification of surface markers involved in osteoblast differentiation pr ovides a method to isolate osteoblasts at various stages of maturation. In this study, we examined expression of the T lymphocyte differentiation anti gen, Thy-1, by osteoblastic cells from different species, Murine skeletal p rogenitor, neonatal calvarial, and adult bone cells (ABCs) were selected to represent osteoblasts at distinct stages of maturation, Flow cytometric an alysis showed that Thy-1 expression was undetectable on the progenitor cell s (mouse limb bud clones 14 and 17), appeared on calvarial cells (45%(+)), and was decreased on ABCs (< 10%(+)). Thy-1 was also detected in situ on os teoblastic cells in mouse calvariae, Thy-1 mRNA expression correlated with cell surface expression. Antigen expression was markedly increased during t he cells' proliferative phase in culture. Furthermore, examination of prima ry rat and human osteoblast-like cells revealed that significant levels of Thy-1 were also expressed on those cells derived from subconfluent culture. This study indicates that osteoblasts express Thy-1 antigen and that its e xpression is maximal at their earliest stage of maturation, during the prol iferative phase, and then declines as the cells mature. In a role similar t o the one it plays in the hematopoietic system, Thy-1 antigen may be useful as a differentiation marker in following the development of the osteoblast .