Effect of Integrins on Mandibular Morphogenesis and CP27 Gene Expression

The developing mandible is a unique craniofacial bone of profound importance for facial shape and dental occlusion. The development and morphogenesis of the mandible is regulated by a network of extracellular matrix/cell-surface interactions, which may include cell-surface receptors such as integrins and CP27, a unique craniofacial protein discovered in our laboratory. Objective: To determine the effect of integrins av and b1 on mandibular morphogenesis and CP27 gene expression. Methods: For temporo-spatial expression and localization analysis, E10, E12, E14, E16, E18, and E20 Swiss-Webster mice were sacrificed and processed for immunohistochemistry. To analyze integrin function as it pertains to mandible growth and development, E11 mandible organs were prepared and cultured for 6 days. During culture, the culture medium was treated with anti-integrin av, anti-integrin b1, or rabbit IgG as a control. To determine the effect of integrin function modulation on pre-osteoblasts, MC3T3 cells were treated with anti-integrin av, anti-integrin b1, or rabbit IgG as a control. Gene expression of CP27, osteocalcin and other extracellular matrix genes was evaluated via RT-PCR. Results: Immunohistochemistry revealed low-level integrin av signals in developing mandibular bone and osteoblasts, while integrin b1 featured strong signals in bone, osteoblasts, and Meckel’s cartilage. Following mandibular organ culture, mandible organs treated with anti-b1 antibody demonstrated a reduction of bone formation. Mandible organs treated with anti-av antibody were reduced in overall mandible size and exhibited an almost complete absence of bone formation. Blockage of integrins av and b1 in MC3T3 cells resulted in a 5-fold downregulation of osteocalcin gene expression and a 2-fold downregulation of CP27 gene expression while expression of other extracellular matrix genes remained unchanged. Conclusion: Our study indicates that integrins and craniofacial proteins such as CP27 contribute to mandibular morphogenesis. This study was supported by NIDCR grant DE13095 to TGHD.