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Figure 2. Possible signaling cascades that may promote the fusion of the mononuclear cells recruited to the DF. Both CSF-1 and ODF are known to promote osteoclast formation, whereas OPG inhibits this by preventing cell-to-cell signaling. The downstream products of the transcription factors c-fos and NF
B that promote osteoclast formation are not yet known. Arrows with crosses ( 
) reflect inhibition of gene expression, whereas other arrows reflect enhancement of gene expression or stimulation of cell fusion.
