Hoxa2 Gene Expression In Rat Mandibular And Tibial Defects Regeneration And Repair Of A Comparative Study

Jaw defect is common especially, which is produced by wound,infection, tumor and congenital disease. So it is very significant toresearch its regenerated mechanism. Cranial maxillofacial skeleton,which is derived from the cranial neural crest ectomesenchyme, whiletrunk appendicular skeleton is from mesenchyme, has a distinctivemechanism of intramembranous ossification. Ectomesenchyme displaysthe activity of various homobox a2 gene during osteoblast differentiation.During the development of embryonic skeleton, Hoxa2 gene is notexpressed in cranial maxillofacial skeleton, while it is positivelyexpressed in trunk appendicular skeleton. And exogenous Hoxa2 canresult in the trans-formation from lower jaw to hyoid bone. The eventshowed that there was some distinct with the mechanism of adult jaw andlimb bone regeneration. In our experiment, through constructed the ratmodel of jaw and tibia bone defect, We compared to the expression ofhoxa2 gene in these calluses by morphology, immunohistochemistry andRT-PCR amplification, and investigated the molecular mechanism of jawbone regeneration.Methods: Twenty healthy and male SD rats were equally dividedinto five groups. Jaw and tibia bone defects that size about 4mm wereconstructed in one side, and another side was constructed as control group.The rats were put to death on day 3, 7, 10, 14 and 21 after the operation. The calluses of jaw and tibia bone were examined by histology,immunohistochemistry and RT-PCR amplification. The samples werefixed in 10% formalin(PH=7.4), decalcified in 10% EDTA (PH=7.6),embedded in paraffin, and carried out HE stain and immunohisto-chemistry by using Hoxa2 antibody; Total RNA was respectivelyextracted from calluses on day 3, 7, 10, 14 and 21 after the operation, aswell as control group. Primers were designed by 636th-880th basesequence of hoxa2 mRNA andβ-actin made inside reference. Theexpression of hoxa2 was examined by RT-PCR amplification.Results: We found that new bone had formed on day 7 afteroperation, defect region was fundamental filled with new bone on day 14,and was not distinct with normal bone tissue on day 21. ThroughImmunohistochemical analysis, we observed that Hoxa2 displayed strongprotein expression in the cell of normal and regeneration tibia, but notfound in jaw bone. The result of RT-PCR amplification was that the genefragment of hoxa2 cDNA, whose length was 245 bp, was detected both inthe repair group and control group in tibia bone, differences wereconsidered significant at p＜0.001. However, the hoxa2 cDNA was notdetected in the jaw bone tissue.Conslusion: The rat model of jaw and tibia bone defect that sizeabout 4mm can heal by itself. During adult bone regeneration, hoxa2 wasexpressed in the tibia and not in the jaw bone, as similarity as embryonic bone development. It was suggested the regeneration of jaw bone maybeexist a distinctive mechanism of molecular regulation.