Progress in biomedical science commonly involves identification of new compounds, the description of novel actions of naturally occurring or exogenously administered agents and clarification of previously unknown interactions underlying physiological or pathophysiological states. Rarer, but none the less exciting are discoveries where two presumably different molecules turn out to be identical. Take bone morphogenesis as a recent example.
Mammalian bone comprises the body's largest site of connective tissue accumulation, which mainly consists of extracellular matrix proteins impregnated by minerals. Type I collagen fibers account for approximately 90% of its extracellular matrix proteins, whereas the remainder includes osteocalcin, osteopontin, osteonectin, fibronectin, thrombospondin and various glycosaminoglycans, in addition to a long list of paracrine or autocrine growth factors. The dynamic balance
Division of Endocrinology, Medizinische Klinik, Klinikum Innenstadt, Ludwig-Maximilians-Universität, München, Germany between local synthesis, deposition and degradation of bone extracellular matrix components plays a crucial role in the body's attempt to adapt