Use of Tritiated Thymidine for the Study of the Origin of the Osteoclast

Abstract

THE origin of the osteoclast has been in question for about a century. So far back as 1873, Kölliker¹ maintained that the osteoclast was formed by the fusion of precursor cells and that these precursor cells were osteoblasts. However, Kölliker's work lacked convincing proof, and as a result, numerous theories appeared concerning the origin of the osteoclast. These theories were based largely on morphological studies of metaphyseal osteoclasts. The presence of numerous cell types at this site makes observation of cellular transitions difficult. In order to circumvent this difficulty, we have examined the distal periosteum of young mouse femora, where numerous osteoclasts appear. The cellular complement of the osteogenic layer of the periosteum generally consists of pre-osteoblasts and osteoblasts.