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The effect of TGF-β 1 on the expression of alkaline phosphatase (ALPase) activity was examined during osteoblastic cell line (MG-63) differentiation induced by 1,25-dihydroxyvitamin D3(1,25D3). TGF-β 1 and 1,25D3were found to enhance ALPase activity. However, preincubation of the cells with 1,25D3transiently abolished the effects of TGF-β 1. Kinetics of the complex responses to TGF-β 1 and 1,25D3were found to correlate well with that of the expression level of type II receptor for TGF-β. These results suggest that 1,25D3may regulate the cellular responses to TGF-β 1 in part via regulation of functional receptor for TGF-β.

A cDNA for the rat bone morphogenetic protein (BMP) type IA receptor (BMPR-IA) was isolated from a dental pulp cell cDNA library. The rat BMPR-IA cDNA encodes a protein of 532 amino acids with a single transmembrane domain and a putative serine/threonine kinase domain. The overall amino acid sequence identity between the rat and human BMPR-IA was 97 %. Reverse transcriptase-polymerase chain reaction analysis revealed that BMPR-IA mRNA was highly expressed in the BMP-induced bone forming tissues throughout the stages tested.

Expression of homeobox genes in relation to ectopic bone formation induced by bone morphogenetic protein (BMP) was investigated. Oligonucleotide primers corresponding to highly conserved regions of Hox cluster and Msx genes were designed to detect homeobox sequences by means of the polymerase chain reaction (PCR). Nine rat homologues of Hox duster genes and two Msx genes were discovered in the BMP-implanted tissue, at earlier stage and later cartilage and bone formation stage, respectively. The PCR study provided evidence of dynamic changes in BMP-induced homeobox gene expression.Copyright 1994, 1999 Academic Press, Inc.