Precise control of jaw length during development is crucial for proper form and function. Previously we have shown that in birds, neural crest mesenchyme (NCM) confers species-specific size and shape to the beak by regulating molecular and histological programs for the induction and deposition of cartilage and bone. Here we reveal that a hitherto unrecognized but similarly essential mechanism for establishing jaw length is the ability of NCM to mediate bone resorption. Osteoclasts are considered the predominant cells that resorb bone, although osteocytes have also been shown to participate in this process. In adults, bone resorption is tightly coupled to bone deposition as a means to maintain skeletal homeostasis. Yet, the role and regulation of bone resorption during growth of the embryonic skeleton have remained relatively unexplored. We compare jaw development in short-beaked quail versus long-billed duck and find that quail have substantially higher levels of enzymes expressed by bone-resorbing cells including tartrate-resistant acid phosphatase (TRAP), Matrix metalloproteinase 13 (Mmp13), and Mmp9. Then, we transplant NCM destined to form the jaw skeleton from quail to duck and generate chimeras in which osteocytes arise from quail donor NCM and osteoclasts come exclusively from the duck host. Chimeras develop quail-like jaw skeletons coincident with dramatically elevated expression of TRAP, Mmp13, and Mmp9. To test for a link between bone resorption and jaw length, we block resorption using a bisphosphonate, osteoprotegerin protein, or an MMP13 inhibitor, and this significantly lengthens the jaw. Conversely, activating resorption with RANKL protein shortens the jaw. Finally, we find that higher resorption in quail presages their relatively lower adult jaw bone mineral density (BMD) and that BMD is also NCM-mediated. Thus, our experiments suggest that NCM not only controls bone resorption by its own derivatives but also modulates the activity of mesoderm-derived osteoclasts, and in so doing enlists bone resorption as a key patterning mechanism underlying the functional morphology and evolution of the jaw.

Neural crest mesenchyme (NCM) controls species-specific pattern in the craniofacial skeleton but how this cell population accomplishes such a complex task remains unclear. To elucidate mechanisms through which NCM directs skeletal development and evolution, we made chimeras from quail and duck embryos, which differ markedly in their craniofacial morphology and maturation rates. We show that quail NCM, when transplanted into duck, maintains its faster timetable for development and autonomously executes molecular and cellular programs for the induction, differentiation, and mineralization of bone, including premature expression of osteogenic genes such as Runx2 and Col1a1. In contrast, the duck host systemic environment appears to be relatively permissive and supports osteogenesis independently by providing circulating minerals and a vascular network. Further experiments reveal that NCM establishes the timing of osteogenesis by regulating cell cycle progression in a stage- and species-specific manner. Altering the time-course of D-type cyclin expression mimics chimeras by accelerating expression of Runx2 and Col1a1. We also discover higher endogenous expression of Runx2 in quail coincident with their smaller craniofacial skeletons, and by prematurely over-expressing Runx2 in chick embryos we reduce the overall size of the craniofacial skeleton. Thus, our work suggests that NCM establishes species-specific size in the craniofacial skeleton by controlling cell cycle, Runx2 expression, and the timing of key events during osteogenesis.

Changes in the oral cavity observed in patients with HPT suggested both decreased cortical density and increased likelihood of oral tori. The contemporary oral manifestations of primary HPT are different from those previously reported, and health care providers should be aware of newer, more subtle findings that may be present when treating patients with HPT.

SUMMARYMany tissue-engineering approaches for repair and regeneration involve transplants between species. Yet a challenge is distinguishing donor versus host effects on gene expression. This study provides a simple molecular strategy to quantify species-specific contributions in chimeras and xenografts. Species-specific primers for reverse transcription quantitative real-time PCR (RT-qPCR) were designed by identifying silent mutations in quail, duck, chicken, mouse and human ribosomal protein L19 (RPL19). cDNA from different pairs of species was mixed in a dilution series and species-specific RPL19 primers were used to generate standard curves. Then quail cells were transplanted into transgenic-GFP chick and resulting chimeras were analyzed with species-specific primers. Fluorescence-activated cell sorting (FACS) confirmed that donor-and host-specific levels of RPL19 expression represent actual proportions of cells. To apply the RPL19 strategy, we measured Runx2 expression in quail-duck chimeras. Elevated Runx2 levels correlated with higher percentages of donor cells. Finally, RPL19 primers also discriminated mouse from human and chick. Thus, this strategy enables chimeras and/or xenografts to be screened rapidly at the molecular level.

The role of AP-1 family members in the action of PTHrP was examined in cementoblasts. PTHrP increased mRNA and protein levels of all Fos members, but only one Jun member (JunB) was increased. Overexpression of JunB in cementoblasts mimicked actions of PTHrP to support osteoclastogenesis and inhibit cementoblast differentiation, suggesting that the actions of PTHrP on mesenchymal cells operate through JunB.Introduction: Cementoblasts are mesenchymal cells that share phenotypic features with osteoblasts in vitro; however, unlike osteoblasts, cementoblasts rarely support osteoclastogenesis in vivo. The osteoblast-mediated support of osteoclastogenesis involves PTH-induced reduction in osteoprotegerin (OPG) expression. PTH acts on osteoblastic cells through specific signaling pathways and transcription factors such as activator protein 1 (AP-1). The purpose of this study was to determine the impact of PTH-related protein (PTHrP) on AP-1 transcription factors in cementoblasts and the role of JunB in the actions of PTHrP. Materials and Methods: Cementoblastic cells were treated with PTHrP and evaluated for mRNA and protein levels of AP-1 family members. Stable transfectants of OCCM cells overexpressing JunB were evaluated for OPG production, ability to support osteoclastogenesis, and measures of proliferation and differentiation. Results: PTHrP treatment in vitro resulted in a time-dependent upregulation of mRNA and proteins for the Fos family members, but only JunB of the Jun family. OPG mRNA and protein levels were reduced by PTHrP in OCCM and were lower in JunB overexpressing cells than controls. In co-culture experiments, TRACP

The 2005-06 officers of the National Student Research Group (NSRG) of the American Association for Dental Research (AADR) have summarized their activities in developing the NSRG into an effective organization aimed at fostering future dental researchers. The officers have focused their efforts on establishing opportunities for the pre-doctoral dental student members of the AADR to participate in and formally present their research during dental school. In addition to the many research awards and fellowships already sponsored by the NSRG and the AADR, the NSRG has established new travel awards for students to present at specialty groups' annual meetings. Other recent initiatives have included a contact list of all dental schools, along with local student research group (SRG) leadership contacts, advice during the creation of a new teaching fellowship opportunity, fundraising efforts to support student research and the NSRG infrastructure, and successfully pursuing a student voting position on the AADR Board. A brief addendum detailing recent activities and future initiatives is also included. The article describes membership requirements, selection of officers, and contacts for additional information. We hope that this Discovery! will serve to increase the awareness of students, researchers, and administrators regarding the role of the NSRG.

Various tissue‐engineering strategies for repair and regeneration involve using cells from different species in chimeras or xenografts. Yet a major challenge is distinguishing between donor‐versus host‐effects on gene expression. This study provides a simple molecular strategy to quantify species‐specific contributions in chimeras and xenografts using species‐specific primers for ribosomal protein L19 (RPL19). cDNA from quail, duck, chicken, mouse, and human was mixed in pairs as a dilution series, species‐specific RPL19 expression was measured, a linear regression was calculated, and the ratios of donor and host cells were estimated. To test the accuracy of the approach, quail cells were transplanted into transgenic‐GFP chick and resulting chimeras were analyzed with species‐specific primers. Fluorescent‐activated cell sorting validated the RPL19 strategy. To apply the RPL19 strategy, Runx2 expression was measured in quail‐duck chimeras. Elevated Runx2 levels correlated with higher percentages of donor cells. Finally, RPL19 primers were also shown to discriminate human‐mouse samples. Thus, this study offers a straightforward and universal strategy that enables chimeras and xenografts to be screened efficiently and rapidly prior to obtaining critical information at the molecular level. Supported by K08 DE021705 and T32 DE007306 from NIDCR to ELE.; R01 DE016402 from the NIDCR to RAS.Grant Funding Source: NIDCR

The jaw shows great evolutionary variation in size. Our recent work demonstrates that skeletal cells derived from neural crest mesenchyme (NCM) control jaw size. Yet mechanisms by which NCM accomplishes this task remain unclear. One scenario is that interactions between NCM and adjacent cells, such as osteoclasts, play a critical role in determining jaw size. Unlike NCM‐derived osteoblasts that make bone, osteoclasts come from the hematopoietic lineage and resorb bone. A finely tuned balance between osteoblast and osteoclast activities may ultimately establish jaw size. Factors known to mediate these interactions include members and targets of the TGFÎ2 signaling pathway. To test if NCM controls jaw size through TGFÎ2 signaling and osteoclasts, we employ a quail‐duck chimeric transplant system. Previously, we have shown that quail donor NCM makes bone by executing autonomous molecular programs within duck hosts. Here, we perform transplants and gain‐ and loss‐of‐function experiments. We find that NCM controls jaw size through TGFÎ2 signaling and by regulating osteoclasts. Funded by NIDCR T32 DE007306 and K08 DE021705A to ELE; NSF DGE‐0648991 to JY; CIHR Fellowship to AHJ; and NIDCR R01 DE016402 to RAS.Grant Funding Source : NIH