Answer:
1931: Huggins reported that epithelial cellls from the mucosa of the urinary tract could stimulate ectopic formation of bone through ingrowth of mesenchymal tissues and subsequent differentiation into bone.
Urist found a specific protein fraction of demineralized bone matrix was responsible for the majority of osteoinductive influences.
BMP is most likely a morphogen and differentiating factor. It is growth hormone dependent and its quantity in bone matrix declines with age.