Paxillin is a target for the tyrosine kinase Src, and Src plays a critical role in osteoclastic bone resorption but not OCL formation.(8) Animals lacking Src form increased numbers of OCLs, but the animals develop osteopetrosis(22) because Src kinase plays an important role in cytoskeletal organization and OCL function. Here, SRC is linked to osteopetrosis.