To understand the precise mechanism of bone formation induced by bone morphogeneticproteins (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, duringectopic 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 thestages tested and that mRNA for activin type IA receptor, which was shown to serve as areceptor for BMP as well, was also expressed. These results suggest that these three receptorsplay important roles for the ectopic bone formation induced by BMP. In addition, expression of mRNAs for TGF-βtype I and type II receptors and activin type IB and type II receptors wasalso detected in the BMP-implanted tissues, which suggested the possible involvement of TGF-βs and activins as ligands in the ectopic bone formation.
The comparison of the rat BMPR-IA with the human and mouse counterparts showed highconservation among species. This finding suggests that BMPs may exert their effects through highly conserved pathway among species.