The lifespan of osteoclasts: experimental studies using the giant granule cytoplasmic marker characteristic of beige mice.

Osteoclasts are large multinucleated skeletal cells that form by fusion of bloodborne mononuclear precursors. Fusion with mononuclear precursors occurs throughout life, and survival of osteoclasts is believed to be dependent upon continued replenishment by fusion. This study examined osteoclast lifespan, defined as maximal survival without fusion, in normal mice irradiated to eliminate host stem cells and rescued with stem cells from beige (bg) mice whose osteoclasts have a distinctive phenotype. Osteoclasts of donor phenotype appeared during the second week and progressively increased so that by the sixth week no osteoclasts of host phenotype were present. Radiation alone did not produce any change in osteoclast phenotype. These data are interpreted to indicate that the maximal survival of osteoclasts without fusion of precursors is less than 6 weeks.