CHARACTERIZATION AND CLONING OF THE E11 ANTIGEN, A MARKER EXPRESSED BY RAT OSTEOBLASTS AND OSTEOCYTES

A new marker for cells of the osteoblastic lineage was identified by r aising monoclonal antibodies against an immortalized rat osteoblastic cell line, Among the different antibodies one was selected which, on t issue sections, strongly reacts with osteoblasts, preosteocytes, and o steocytes, This antibody, designated Ell, recognizes an antigen locali zed at the cell surface, The cDNA encoding the Ell antigen was cloned from a cDNA library prepared from ROS 17/2.8 cells, using a eukaryotic expression system, The Ell cDNA sequence revealed homology with the m urine OTS-8/gp38 sequence, In situ hybridization confirmed that Ell mR NA expression in bone is restricted to osteoblasts and osteocytes, The tissue specificity of the Ell expression was studied by immunohistoch emistry and Northern blot analysis, Apart from bone, Ell-positive cell s were also found in lung: namely, the alveolar cells of type I, Epith elial cells of the choroid plexus and endothelial cells of lymphatic v essels were also labeled with mAb Ell, These results were confirmed by Northern blot, as the 1.8 kb Ell mRNA transcript was detected in bone and also in lung, brain, and skin, In conclusion, we describe a novel osteoblastic product which is expressed by mature osteoblasts and new ly formed osteocytes.