Bone marrow cells isolated from long bones of a ddY mouse were cultured on sperm whale dentin and examined by light, scanning and transmission electron microscopy. The osteoclasts in vitro showed essentially the same ultrastructures as in vivo. The distribution of actin in the osteoclasts was examined by an indirect immunofluorescent antibody method, which revealed a wide ring-shaped area under the fluorescence microscope. Transmission electron microscopy showed that the ring-shaped area corresponded to the clear zone. The clear zone and resorption lacunae were examined by a double illuminating method to determine the relationship between the clear zone and the lacunae, which could be divided into three types. The distribution and function of the clear zone are discussed.
Actins Animals