IMMUNOHISTOCHEMICAL DETECTION OF ACTIVIN-A IN OSTEOCLASTS

Production of a member of transforming growth factor-beta (TGF-beta) s uperfamily, activin A, was examined in the bone tissue by using revers e transcriptase polymerase reaction. As a result, specific bands were detected showing the presence of activin A mRNA in the bone tissues. T n order to localize the production site of activin A in the bone tissu es, we tried to immunolocalize activin A in fetal mouse calvaria cultu red in a medium containing fetal calf serum, 1 alpha-25(OH)(2) vitamin D-3 and parathyroid hormone. In these cultured calvaria, bone tissues including bone-resorbing osteoclasts in vitro were observed. Positive staining demonstrating the presence of activin A resided inside of th e multinucleated cells in the bone-resorbing lacunae, suggesting the p roduction of activin A in osteoclasts. Activin A was also localized im munohistochemically in the osteoclast-like multinucleated cells develo ped in vitro. These results suggest that osteoclasts produce activin i n the bone tissues and that activin may play some roles by autocrine a nd/or paracrine manner in bone metabolisms.