Osteoclast precursors and macrophages

Osteoclasts (OCs) share a common origin with macrophages. Our experiments have shown that macrophage-colony stimulation factor (M-CSF) dependent cells from mouse bone marrow and spleen are capable of been turned into multinucleated tartrate-resistant acidic phosphatase (TRAP) positive cells with up to 150 nuclei. Macrophages retrieved from mouse peritoneal cavity with thioglycollate medium were also OCs inducible. But cells with only three nuclei at most were generated when same experimental conditions were used. It is not surprised because macrophages from peritoneal cavity were matural cells so that different from osteoclast-committed osteoclast precursors. The question is: why RAW264.7, a peritoneal macrophage cell line transformed by Abelson leukemia virus, can be turned into huge osteoclasts, even in the absence of M-CSF?