The developmental relationship between osteocytes and osteoclasts: A study using the quail-chick nuclear marker in endochondral ossification

Abstract

Interspecific grafts of limb buds and femurs on the chorioallantoic membrane of 5-day-old hosts and into the somatopleure of 3-day-old hosts were carried out between quail and chick embryos. Due to their different nuclear features, the cells of the two species can be identified in the chimeric bones resulting from the endochondral ossification which occurs in the explanted tissues. By following the cell lineage in the bone and marrow we were able to show that the hemopoietic and the osteogenic (comprising osteoblasts, osteocytes, and chondrocytes) cell lines have different embryological origins. The osteogenic line is derived from the limb bud mesenchyme, while the hemopoietic cells are brought into the bone marrow via the circulation. In the fixed cells of the marrow two categories have to be distinguished: the reticular cells originating from the bone rudiment and the endothelial cells which invade the cartilage and are of hematogenous origin. The osteoclasts belong to the hemopoietic cell line and are not derived from any cell type of the osteogenic line.