UCSF

Mesenchymal Regulation of Jaw Bone Length

Erin Lynn Ealba

With the goal of devising new therapies for skeletal diseases, injuries, and birth defects, there is keen interest to discover mechanisms through which mesenchymal cells make bone. Many studies have pointed to molecular factors that induce the osteogenic differentiation of mesenchyme in vitro, but since a clinical objective is to engineer mesenchyme for applications in vivo, more work is required to identify critical interactions between osteogenic mesenchyme and surrounding tissues, such as osteoclasts. In the developing jaws and face, all bone comes from neural crest mesenchyme (NCM) whereas osteoclasts arise from mesoderm. We take advantage of these distinct embryonic origins and transplant faster developing quail NCM into slower developing duck embryos. Previously, using this quail-duck chimeric system, we have shown that NCM makes bone by executing autonomous molecular and histogenic programs. Here, I assess the effects of NCM and their effects on host-derived osteoclasts by using histology and immunochemistry (Milligan's Trichrome, Q¢PN, Tartrate-resistant acid phosphatase (TRAP)), whole-mount staining analysis (TRAP, alizarin red), gene expression (in situs, RNA isolation, cDNA synthesis, reverse transcription quantitative real-time PCR (RT-qPCR)), Cloning (PCR, pGEM-T Easy), Fluorescence-Activated Cell Sorting (FACS), proliferation analysis (BrdU, ImageJ), Inhibiting and activating resorption (Alendronate, matrix metalloproteinase 13 (MMP13) inhibitor, recombinant osteoprotogerin (rOPG), recombinant receptor activator of nuclear factor κ β (rRANKL)), and morphometric analysis. We find that the influence of NCM on osteoclast activity has direct implications for differences in craniofacial elements. We conclude that the timing of matrix remodeling plays an important role in determining jaw length.