Where did bone come from?

Bone is specific to vertebrates, and originated as mineralization around the basal membrane of the throat or skin, giving rise to tooth-like structures and protective shields in animals with a soft cartilage-like endoskeleton. A combination of fossil anatomy and genetic information from modern species has improved our understanding of the evolution of bone. Thus, even in man, there are still similarities in the molecular regulation of skin appendages and bone.

BMPs: from bone to body morphogenetic proteins.

The family of bone morphogenetic proteins (BMPs) comprises approximately 30 secreted cytokines that signal through transmembrane serine/threonine kinase receptors. The BMP signaling pathways are fine-tuned on multiple levels: Extracellular antagonists modify ligand activity; several co-receptors enhance or inhibit downstream signaling events through multiple mechanisms; and intracellular molecules further regulate the signaling outcome and mediate crosstalk with other pathways. BMPs affect structures and processes throughout the entire body, ranging from embryonic patterning and development through stem cells and their niches, to tissue homeostasis and regeneration.