Immunohistochemical investigations on the differentiation marker protein E11 in rat calvaria, calvaria cell culture and the osteoblastic cell line ROS 17/2.8.

Until now, many extracellular matrix proteins, e.g. osteopontin and osteonectin, have been used to determine a cell's osteogenic maturation. The disadvantage in evaluation of these proteins is their relative wide-ranging appearance throughout the osteogenic differentiation process. Thus, the aim of this study was to establish an immunohistochemical setup using E11, a marker that binds selectively to cells of the late osteogenic cell lineage. In addition, the histochemical expression of the bone matrix proteins osteonectin, osteopontin and fibronectin was compared to that of E11 using monoclonal antibodies. For light microscopical detection of osteogenic markers in cultured cells we developed a simple paraffin technique using a fibrin glue as embedding medium. This allows the handling of cultured cells such as a tissue sample and includes the use of stored biological specimens for further immunohistochemical experiments. We used newborn rat calvariae for whole tissue preparations and for isolation and cultivation of bone cells. In addition, we included the rat osteosarcoma cell line ROS 17/2.8 in this study. For the first time, we have localised E11 in osteocytes of rat calvaria preparations at the electron microscopical level. E11 was detected at plasma membranes of osteocytes and their processes, but not at those of osteoblasts. Accompanying experiments with cultured newborn rat calvaria cells and ROS 17/2.8 cells revealed E11 reactivity on a subset of cells. The results obtained confirm the suitability of the differentiation marker E11 as a sensitive instrument for the characterisation of bone cell culture systems.