Morphological and molecular analyses of bone repair

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Although bone is one of tissues with strong regenerating ability, molecular mechanism of bone repair has not been fully understood. In order to investigate molecular mechanism of bone repair by analysis of changes in gene expression during fracture healing, we conducted several experiments and obtained the following results.We first examined expression of several mRNAs after fracture of mouse ribs by RT-PCR.Apparent mRNAs for Sonic hedgehog (Shh) and Indian hedgehog (Ihh) were not found in ribes before fracture. After 12-24 hours of fracture, we found substantial level of Shh mRNA.Its expression decreased after 48-72 hours of fracture. No Shh mRNA was found on day 5 after fracture. Expression for Ihh mRNA was found after 3 days of fracture. Expression of BMP-2 mRNA increased after 24-48 hours of fracture, while no apparent changes in expression of BMP-4 and BMP-7 mRNAs was found. These results indicated that Shh may play an important role in induction of BMP-2 at early phase of fracture repair. In addition, expression of mRNA for Cbfa1, which is an essential transcription factor of osteoblast differentiation and bone formation, increased after 72 hours of fracture. We are now investigating the expression pattern of these genes by in situ hybridization.