Distribution of osteonectin mRNA and protein during human embryonic and fetal development.

We investigated the temporal and spatial distribution of osteonectin during human embryonic and fetal development, using in situ hybridization and immunohistochemistry. Osteonectin gene expression was generally found in cells exhibiting high rates of matrix production/proliferation. In mineralized tissue, a strong signal was obtained in osteoblasts, odontoblasts, and chondrocytes of the upper hypertrophic and proliferative zones. Chondrocytes of the mineralized zone showed no expression throughout the different stages of development. Strong osteonectin expression was found in odontoblasts of developing teeth. In addition, osteonectin mRNA and protein were detected in several non-mineralized tissues: steroid-producing cells of the adrenal gland and the gonads, kidney (glomeruli), lung (bronchi), skin, megacaryocytes, and large vessels. Histochemistry confirmed the results and detected extracellular osteonectin in bone and in the zone of mineralized cartilage only. The localization of osteonectin in bone, cartilage, and teeth is consistent with a role in the initiation of mineralization. However, the organ-specific distribution in non-mineralized tissues suggests an important multifunction role of this protein during human development.