Expression of serine/threonine kinase receptors during ectopic bone formation induced by bone morphogenetic protein (BMP).

To understand the precise mechanism of bone formation induced by bone morphogenetic proteins (BMPs), it is important to elucidate the receptor system of BMPs. In this study, expression of mRNAs for serine/threonine kinase receptors, including BMP receptors, during ectopic bone formation induced by BMP, was investigated, and also the molecular cloning of rat BMP type IA receptor (BMPR-IA) was performed. Polymerase chain reaction (PCR)-based analysis revealed that mRNAs for BMP type IA and type IB receptors were expressed in the BMP-induced bone forming tissues throughout the stages tested and that mRNA for activin type IA receptor, which was shown to serve as a receptor for BMP as well, was also expressed. These results suggest that these three receptors play important roles for the ectopic bone formation induced by BMP. In addition, expression of mRNAs for TGF-beta type I and type II receptors and activin type IB and type II receptors was also detected in the BMP-implanted tissues, which suggested the possible involvement of TGF-betas and activins as ligands in the ectopic bone formation. The comparison of the rat BMPR-IA with the human and mouse counterparts showed high conservation among species. This finding suggests that BMPs may exert their effects through highly conserved pathway among species.