Expression of calcitonin receptors during osteoclast differentiation in mouse metatarsals

Metatarsal bones of 15-day-old mouse embryos contain proliferative tartrate-resistant acid phosphatase (TRAP) negative (-) osteoclast progenitors that progressively differentiate into multinucleated TRAP positive (+) osteoclasts. Using histochemical and autoradiographic techniques, we have examined the expression of calcitonin receptors during osteoclast differentiation in mouse metatarsals. Fresh mouse metatarsals from embryos aged 14-17 days and metatarsals from 15-day-old embryos cultured for 1, 2, 3, and 6 days were stained for TRAP. Calcitonin binding to osteoclasts and their precursors was studied by incubating metatarsals with [125I]salmon calcitonin (sCT) and quantitating grain counts from autoradiographs of tissue sections. Calcitonin receptors first appear on nonproliferating osteoclast precursors, most often just after or simultaneously with the development of TRAP activity. The effect of sCT on the development of TRAP+ mononuclear preosteoclasts was examined by culturing 15-day-old metatarsals in the continuous presence of 5 mU sCT for periods of up to 3 days and quantitating the number of TRAP+ mononuclear preosteoclasts that develop. Calcitonin did not affect the differentiation of osteoclasts up to the stage of the TRAP+ mononuclear preosteoclast.