Local regulation of craniofacial osteogenesis by neural crest stem cells

Objective: Craniofacial bones such as the maxilla and mandible originate from neural crest stem cells (NCSCs) that undergo intramembranous ossification. Although several studies have focused on the in vivo patterning of individual bones, there has been little work on mechanisms controlling the timing of bone formation. Understanding the temporal regulation of craniofacial osteogenesis is a prerequisite for advancing stem cell- and molecular-based therapies to treat clinical conditions specific to the face and jaw.

Methods: Avians are an ideal model system for such investigations due to the availability and accessibility of their embryos. In particular, quail and duck, which show relatively large differences in their embryonic maturation rates (17 versus 28 days to hatching, respectively), can be exploited to identify molecular mechanisms that control the timing of key events during craniofacial osteogenesis such as osteocyte specification, proliferation, matrix deposition, and mineralization. Moreover, the integration of other processes that may influence osteogenesis, such as vascularization and resorption, can also be studied concomitantly. Unilateral transplants of premigratory NCSCs were performed between stage-matched duck and quail embryos. Chimeras were grown to specific stages corresponding to the progression of osteogenesis. Molecular, cellular, and histological analyses were undertaken to identify donor-induced changes in the timing of osteogenesis. Alterations to vasculogenesis and osteoclast activity in the host were also assayed by injecting fluorescent microbeads and whole-embyro TRAP staining, respectively.

Results: NCSC-derived mesenchyme controls the timing of osteocyte specification, proliferation, matrix deposition, and mineralization. In addition, vasculogenesis and osteoclast activity are influenced in the host.

Conclusion: Our results demonstrate that the NCSC-derived local environment predominantly regulates the timing of each step during craniofacial osteogenesis.