Spry1 and spry2 are essential for development of the temporomandibular joint

Transmission electron microscopic study of the surface layer of surgical resected disc specimens in human temporomandibular joint

In this study, we investigated specific and characteristic findings of the surface layer of surgical resected disc specimens in human temporomandibular joint osteoarthritis cases by transmission electron microscopy (TEM).Specimens were surgically removed from the TMJ of 5 cases (4 female patients: 5 cases) clinically osteoarthritis. Following findings were observed by TEM. Images were photographed on a JEM1400-Flash Electron microscope (JEOL, Japan) equipped with an EM-14661FLASH high-sensitivity digital complementary metal-oxide-semiconductor camera.Following findings were observed by TEM. 1) The surface is covered with plump fibroblastic and histiocytoid cells. 2) Collagen fiber bundles and collagenous matrix are exposed onto the eroded disc surface. 3) Fibrinous dense material is observed on the eroded disc surface. 4) Bundles of collagen fibers are densely observed. 5) Collagen bundles are rich around capillary vessels. 6) Synovial surface cells reveal features of activated macrophages with vacuole formation. Especially, plump fibroblastic and histiocytoid cells, and activated macrophages with vacuole, which were significant findings of the surface layer. These findings might have a significant effect on the regulation of synovial fluid.

Evolution and development of the mammalian jaw joint: Making a novel structure

A jaw joint between the squamosal and dentary is a defining feature of mammals and is referred to as the temporomandibular joint (TMJ) in humans. Driven by changes in dentition and jaw musculature, this new joint evolved early in the mammalian ancestral lineage and permitted the transference of the ancestral jaw joint into the middle ear. The fossil record demonstrates the steps in the cynodont lineage that led to the acquisition of the TMJ, including the expansion of the dentary bone, formation of the coronoid process, and initial contact between the dentary and squamosal. From a developmental perspective, the components of the TMJ form through tissue interactions of muscle and skeletal elements, as well as through interaction between the jaw and the cranial base, with the signals involved in these interactions being both biomechanical and biochemical. In this review, we discuss the development of the TMJ in an evolutionary context. We describe the evolution of the TMJ in the fossil record and the development of the TMJ in embryonic development. We address the formation of key elements of the TMJ and how knowledge from developmental biology can inform our understanding of TMJ evolution.

The Temporomandibular Joint: A Critical Review of Life-Support Functions, Development, Articular Surfaces, Biomechanics and Degeneration

The temporomandibular joint is a highly conserved articulation because it promotes survival and propagation via the essential functions of mastication, communication, and routine mating success (dentofacial esthetics). The temporomandibular joint is a unique secondary joint formed between the endochondral temporal bone and the mandibular secondary condylar cartilage via Indian hedgehog and bone morphogenetic protein signaling that is closely related to ear development. A dynamic epigenetic environment is provided by Spry1 and Spry2 genetic induction of the lateral pterygoid and temporalis muscles. Mechanical loading of the condylar periosteum during fetal development produces a superficial layer of fibrocartilage that separates from the condyle to form the interposed temporomandibular joint disc. The articular surfaces of the condyle and fossa are dynamically modified periosteum that has healing and regenerative capability. This unique tissue is composed of a superficial fibrous layer (synovial surface) with an underlying proliferative (cambium) layer that produces a cushioning layer of fibrocartilage which subsequently forms bone. Prior to occlusion of the first primary (deciduous) molars at about 16 months, facial development is dominated by primary genetic mechanisms. After achieving posterior functional occlusion, biomechanics enhances temporomandibular joint maturation, and assumes control of facial growth, development and adaptation. Concurrently, hypothalamus control of musculoskeletal physiology shifts from insulin-like growth factor IGF2 to IGF1, which affects bone via muscular loading (biomechanics). Three layers of temporomandibular joint fibrocartilage are resistant to heavy functional loading, but parafunctional clenching may result in degeneration that is first manifest as trabecular sclerosis of the mandibular condyle.

The TMJ Disc Is a Common Ancestral Feature in All Mammals, as Evidenced by the Presence of a Rudimentary Disc During Monotreme Development

The novel mammalian jaw joint, known in humans as the temporomandibular joint or TMJ, is cushioned by a fibrocartilage disc. This disc is secondarily absent in therian mammals that have lost their dentition, such as giant anteaters and some baleen whales. The disc is also absent in all monotremes. However, it is not known if the absence in monotremes is secondary to the loss of dentition, or if it is an ancestral absence. We use museum held platypus and echidna histological sections to demonstrate that the developing monotreme jaw joint forms a disc primordium that fails to mature and become separated from the mandibular condyle. We then show that monotreme developmental anatomy is similar to that observed in transgenic mouse mutants with reduced cranial musculature. We therefore suggest that the absence of the disc on monotremes is a consequence of the changes in jaw musculature associated with the loss of adult teeth. Taken together, these data indicate that the ancestors of extant monotremes likely had a jaw joint disc, and that the disc evolved in the last common ancestor of all mammals.

Rat mandibular condyle and fossa grew separately then unified as a single joint at 20 days old, which was the weaning age

Magnetic resonance imaging (MRI) was used to observe growth of the mandibular condyle, mandibular fossa, and articular disc as a single unit. Changes in each component's relative position and size were observed using 7-tesla MRI. Mandibular condyle chondrocytes' growth was evaluated with immunohistochemistry, using the expression of zinc transporter ZIP13. Three-dimensional T₁-weighted (T_1w) MRI was used to obtain images of the TMJ of Sprague Dawley rats at 4-78 days old (P4-78) with a voxel resolution of 65 μm. Two-dimensional T_1w MR images were acquired after a subcutaneous injection of the contrast reagent gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA). The T_1w MR images showed that the mandibular condyle was located posterior to the mandibular fossa until P20; however, it then moved to a location underneath the mandibular fossa. In the Gd-DTPA enhanced images, the articular disc was identified as a region with lower signal intensity from P20. The number of ZIP13-positive chondrocytes at P6 was larger than the number at P24. In conclusion, the mandibular condyle with cartilage and disc grows on the posterior side of the mandibular fossa until P20, which was the weaning age. Then, the condyle fit into the mandibular fossa and completed the functional unit.

Evidence of vasculature and chondrocyte to osteoblast transdifferentiation in craniofacial synovial joints: Implications for osteoarthritis diagnosis and therapy

Temporomandibular joint osteoarthritis (TMJ OA) leads to permanent cartilage destruction, jaw dysfunction, and compromises the quality of life. However, the pathological mechanisms governing TMJ OA are poorly understood. Unlike appendicular articular cartilage, the TMJ has two distinct functions as the synovial joint of the craniofacial complex and also as the site for endochondral jaw bone growth. The established dogma of endochondral bone ossification is that hypertrophic chondrocytes undergo apoptosis, while invading vasculature with osteoprogenitors replace cartilage with bone. However, contemporary murine genetic studies support the direct differentiation of chondrocytes into osteoblasts and osteocytes in the TMJ. Here we sought to characterize putative vasculature and cartilage to bone transdifferentiation using healthy and diseased TMJ tissues from miniature pigs and humans. During endochondral ossification, the presence of fully formed vasculature expressing CD31⁺ endothelial cells and α-SMA⁺ vascular smooth muscle cells were detected within all cellular zones in growing miniature pigs. Arterial, endothelial, venous, angiogenic, and mural cell markers were significantly upregulated in miniature pig TMJ tissues relative to donor matched knee meniscus fibrocartilage tissue. Upon surgically creating TMJ OA in miniature pigs, we discovered increased vasculature and putative chondrocyte to osteoblast transformation dually marked by COL2 and BSP or RUNX2 within the vascular bundles. Pathological human TMJ tissues also exhibited increased vasculature, while isolated diseased human TMJ cells exhibited marked increased in vasculature markers relative to control 293T cells. Our study provides evidence to suggest that the TMJ in higher order species are in fact vascularized. There have been no reports of cartilage to bone transdifferentiation or vasculature in human-relevant TMJ OA large animal models or in human TMJ tissues and cells. Therefore, these findings may potentially alter the clinical management of TMJ OA by defining new drugs that target angiogenesis or block the cartilage to bone transformation.

Morphological association between the muscles and bones in the craniofacial region

The strains of inbred laboratory mice are isogenic and homogeneous for over 98.6% of their genomes. However, geometric morphometric studies have demonstrated clear differences among the skull shapes of various mice strains. The question now arises: why are skull shapes different among the mice strains? Epigenetic processes, such as morphological interaction between the muscles and bones, may cause differences in the skull shapes among various mice strains. To test these predictions, the objective of this study is to examine the morphological association between a specific part of the skull and its adjacent muscle. We examined C57BL6J, BALB/cA, and ICR mice on embryonic days (E) 12.5 and 16.5 as well as on postnatal days (P) 0, 10, and 90. As a result, we found morphological differences between C57BL6J and BALB/cA mice with respect to the inferior spine of the hypophyseal cartilage or basisphenoid (SP) and the tensor veli palatini muscle (TVP) during the prenatal and postnatal periods. There was a morphological correlation between the SP and the TVP in the C57BL6J, BALB/cA, and ICR mice during E15 and P0. However, there were not correlation between the TVP and the SP during P10. After discectomy, bone deformation was associated with a change in the shape of the adjacent muscle. Therefore, epigenetic modifications linked to the interaction between the muscles and bones might occur easily during the prenatal period, and inflammation seems to allow epigenetic modifications between the two to occur.

FGF signaling patterns cell fate at the interface between tendon and bone

Tendon and bone are attached by a transitional connective tissue that is morphologically graded from tendinous to osseous and develops from bipotent progenitors that co-express scleraxis (Scx) and Sox9 (Scx⁺/Sox9⁺). Scx⁺/Sox9⁺ progenitors have the potential to differentiate into either tenocytes or chondrocytes, yet the developmental mechanism that spatially resolves their bipotency at the tendon-bone interface during embryogenesis remains unknown. Here, we demonstrate that development of Scx⁺/Sox9⁺ progenitors within the mammalian lower jaw requires FGF signaling. We find that loss of Fgfr2 in the mouse tendon-bone interface reduces Scx expression in Scx⁺/Sox9⁺ progenitors and induces their biased differentiation into Sox9⁺ chondrocytes. This expansion of Sox9⁺ chondrocytes, which is concomitant with decreased Notch2-Dll1 signaling, prevents formation of a mixed population of chondrocytes and tenocytes, and instead results in ectopic endochondral bone at tendon-bone attachment units. Our work shows that FGF signaling directs zonal patterning at the boundary between tendon and bone by regulating cell fate decisions through a mechanism that employs Notch signaling.

The Interaction of Genetic Background and Mutational Effects in Regulation of Mouse Craniofacial Shape

Inbred genetic background significantly influences the expression of phenotypes associated with known genetic perturbations and can underlie variation in disease severity between individuals with the same mutation. However, the effect of epistatic interactions on the development of complex traits, such as craniofacial morphology, is poorly understood. Here, we investigated the effect of three inbred backgrounds (129X1/SvJ, C57BL/6J, and FVB/NJ) on the expression of craniofacial dysmorphology in mice (Mus musculus) with loss of function in three members of the Sprouty family of growth factor negative regulators (Spry1, Spry2, or Spry4) in order to explore the impact of epistatic interactions on skull morphology. We found that the interaction of inbred background and the Sprouty genotype explains as much craniofacial shape variation as the Sprouty genotype alone. The most severely affected genotypes display a relatively short and wide skull, a rounded cranial vault, and a more highly angled inferior profile. Our results suggest that the FVB background is more resilient to Sprouty loss of function than either C57 or 129, and that Spry4 loss is generally less severe than loss of Spry1 or Spry2 While the specific modifier genes responsible for these significant background effects remain unknown, our results highlight the value of intercrossing mice of multiple inbred backgrounds to identify the genes and developmental interactions that modulate the severity of craniofacial dysmorphology. Our quantitative results represent an important first step toward elucidating genetic interactions underlying variation in robustness to known genetic perturbations in mice.

Implications of Vertebrate Craniodental Evo-Devo for Human Oral Health

Highly processed diets eaten by postindustrial modern human populations coincide with higher frequencies of third molar impaction, malocclusion, and temporomandibular joint disorders that affect millions of people worldwide each year. Current treatments address symptoms, not causes, because the multifactorial etiologies of these three concerns mask which factors incline certain people to malocclusion, impaction, and/or joint issues. Deep scientific curiosity about the origins of jaws and dentitions continues to yield rich insights about the developmental genetic mechanisms that underpin healthy craniodental morphogenesis and integration. Mounting evidence from evolution and development (Evo-Devo) studies suggests that function is another mechanism important to healthy craniodental integration and fit. Starting as early as weaning, softer diets and thus lower bite forces appear to relax or disrupt integration of oral tissues, alter development and growth, and catalyze impaction, malocclusion, and jaw joint disorders. How developing oral tissues respond to bite forces remains poorly understood, but biomechanical feedback seems to alter balances of local bone resorption and deposition at the tooth-bone interface as well as affect tempos and amounts of facial outgrowth. Also, behavioral changes in jaw function and parafunction contribute to degeneration and pain in joint articular cartilages and masticatory muscles. The developmental genetic contribution to craniodental misfits and disorders is undeniable but still unclear; however, at present, human diet and jaw function remain important and much more actionable clinical targets. New Evo-Devo studies are needed to explain how function interfaces with craniodental phenotypic plasticity, variation, and evolvability to yield a spectrum of healthy and mismatched dentitions and jaws.

A Joint Less Ordinary: Intriguing Roles for Hedgehog Signalling in the Development of the Temporomandibular Synovial Joint

This review highlights the essential role of Hedgehog (Hh) signalling in the developmental steps of temporomandibular joint (TMJ) formation. We review evidence for intra- and potentially inter-tissue Hh signaling as well as Glioma-Associated Oncogene Homolog (GLI) dependent and independent functions. Morphogenesis and maturation of the TMJ’s individual components and the general landscape of Hh signalling is also covered. Comparison of the appendicular knee and axial TMJ also reveals interesting differences and similarities in their mechanisms of development, chondrogenesis and reliance on Hh signalling.

Sprouty2 regulates endochondral bone formation by modulation of RTK and BMP signaling

Skeletal development is regulated by the coordinated activity of signaling molecules that are both produced locally by cartilage and bone cells and also circulate systemically. During embryonic development and postnatal bone remodeling, receptor tyrosine kinase (RTK) superfamily members play critical roles in the proliferation, survival, and differentiation of chondrocytes, osteoblasts, osteoclasts, and other bone cells. Recently, several molecules that regulate RTK signaling have been identified, including the four members of the Sprouty (Spry) family (Spry1-4). We report that Spry2 plays an important role in regulation of endochondral bone formation. Mice in which the Spry2 gene has been deleted have defective chondrogenesis and endochondral bone formation, with a postnatal decrease in skeletal size and trabecular bone mass. In these constitutive Spry2 mutants, both chondrocytes and osteoblasts undergo increased cell proliferation and impaired terminal differentiation. Tissue-specific Spry2 deletion by either osteoblast- (Col1-Cre) or chondrocyte- (Col2-Cre) specific drivers led to decreased relative bone mass, demonstrating the critical role of Spry2 in both cell types. Molecular analyses of signaling pathways in Spry2(-/-) mice revealed an unexpected upregulation of BMP signaling and decrease in RTK signaling. These results identify Spry2 as a critical regulator of endochondral bone formation that modulates signaling in both osteoblast and chondrocyte lineages.

Augmented Indian hedgehog signaling in cranial neural crest cells leads to craniofacial abnormalities and dysplastic temporomandibular joint in mice

Extensive studies have pinpointed the crucial role of Indian hedgehog (Ihh) signaling in the development of the appendicular skeleton and the essential function of Ihh in the formation of the temporomandibular joint (TMJ). In this study, we have investigated the effect of augmented Ihh signaling in TMJ development. We took a transgenic gain-of-function approach by overexpressing Ihh in the cranial neural crest (CNC) cells using a conditional Ihh transgenic allele and the Wnt1-Cre allele. We found that Wnt1-Cre-mediated tissue-specific overexpression of Ihh in the CNC lineage caused severe craniofacial abnormalities, including cleft lip/palate, encephalocele, anophthalmos, micrognathia, and defective TMJ development. In the mutant TMJ, the glenoid fossa was completely absent, whereas the condyle and the articular disc appeared relatively normal with slightly delayed chondrocyte differentiation. Our findings thus demonstrate that augmented Ihh signaling is detrimental to craniofacial development, and that finely tuned Ihh signaling is critical for TMJ formation. Our results also provide additional evidence that the development of the condyle and articular disc is independent of the glenoid fossa.

Genetic Influences on Temporomandibular Joint Development and Growth

The temporomandibular joint (TMJ) is a small synovial joint at which the mandible articulates with the skull during movements involved in speaking and mastication. However, the secondary cartilage lining its joint surfaces is indicative of a very different developmental history than limb cartilages. This review summarizes our current knowledge of genes that regulate the formation of primary components of the TMJ, as well as genes that regulate postnatal growth of the TMJ. Although the TMJ is regulated by some of the same genes that are important in limb joints, others appear unique to the TMJ or have different actions. Runx2, Sox9, and members of the TGF-β/BMP family are critical drivers of chondrogenesis during condylar cartilage morphogenesis, and Indian hedgehog (Ihh) is important for formation of the articular disc and cavitation. Osterix (Osx) is a critical regulator of endochondral bone formation during postnatal TMJ growth.

Mouse genetic models for temporomandibular joint development and disorders

The temporomandibular joint (TMJ) is a synovial joint essential for hinge and sliding movements of the mammalian jaw. Temporomandibular joint disorders (TMD) are dysregulations of the muscles or the TMJ in structure, function, and physiology, and result in pain, limited mandibular mobility, and TMJ noise and clicking. Although approximately 40-70% adults in the USA have at least one sign of TMD, the etiology of TMD remains largely unknown. Here, we highlight recent advances in our understanding of TMD in mouse models.

Gene Mutations Associated with Temporomandibular Joint Disorders: A Systematic Review

Background

The temporomandibular joint (TMJ) is a bilateral synovial joint between the mandible and the temporal bone of the skull. TMJ disorders (TMDs) are a set of complicated and poorly understood clinical conditions, in which TMDs are associated with a number of symptoms including pain and limited jaw movement. The increasing scientific evidence suggests that genetic factors play a significant role in the pathology of TMDs. However, the underlying mechanism of TMDs remains largely unknown.

Objective

The study aimed to determine the associated genes to TMDs in humans and animals.

Methods

The literature search was conducted through databases including Medline (Ovid), EMBASE (Ovid), and PubMed (NLM) by using scientific terms for TMDs and genetics in March 2015. Additional studies were identified by searching bibliographies of highly relevant articles and Scopus (Elsevier).

Results

Our systematic analyses identified 31 articles through literature searches. A total of 112 genes were identified to be significantly and specifically associated with TMDs.

Conclusion

Our systematic review provides a list of accurate genes associated with TMDs and suggests a genetic contribution to the pathology of TMDs.

The developing story of Sprouty and cancer

Sprouty proteins are evolutionarily conserved modulators of MAPK/ERK pathway. Through interacting with an increasing number of effectors, mediators, and regulators with ultimate influence on multiple targets within or beyond ERK, Sprouty orchestrates a complex, multilayered regulatory system and mediates a crosstalk among different signaling pathways for a coordinated cellular response. As such, Sprouty has been implicated in various developmental and physiological processes. Evidence shows that ERK is aberrantly activated in malignant conditions. Accordingly, Sprouty deregulation has been reported in different cancer types and shown to impact cancer development, progression, and metastasis. In this article, we have tried to provide an overview of the current knowledge about the Sprouty physiology and its regulatory functions in health, as well as an updated review of the Sprouty status in cancer. Putative implications of Sprouty in cancer biology, their clinical relevance, and their proposed applications are also revisited. As a developing story, however, role of Sprouty in cancer remains to be further elucidated.

Sprouty 1 predicts prognosis in human epithelial ovarian cancer

Sprouty proteins are evolutionary-conserved modulators of receptor tyrosine kinase (RTK) signaling. We have previously reported inverse correlation of the Sprouty 1 (Spry1) protein expression with ovarian cancer cell proliferation, migration, invasion and survival. In the present study, the expression status of Spry1 protein and its clinical relevance in patients with epithelial ovarian cancer were explored. Matched tumor and normal tissue samples from 100 patients with epithelial ovarian cancer were immunohistochemically stained for Spry1. Expression of ERK, p-ERK, Ki67, FGF-2, VEGF and IL-6 and their correlation with Spry1 were also evaluated. In addition, correlation between Spry1 and clinicopathological characteristics and predictive significance of Spry1 for overall survival (OS) and disease-free survival (DFS) were analysed. Our data indicated that Spry1 was significantly downregulated in tumor tissues (p=0.004). Spry1 showed significant inverse correlation with p-ERK/ERK (p=0.045), Ki67 (p=0.010), disease stage (p=0.029), tumor grade (p=0.037), recurrence (p=0.001) and lymphovascular invasion (p=0.042). It was revealed that Spry1 low-expressing patients had significantly poorer OS (p=0.010) and DFS (p=0.012) than those with high expression of Spry1. Multivariate analysis showed that high Spry1 (p=0.030), low stage (p=0.048) and no residual tumor (p=0.007) were independent prognostic factors for a better OS, among which high Spry1 (p=0.035) and low stage (p=0.035) remained as independent predictors of DFS, too. We also found that the expression of Spry1 significantly correlates with the expression of Spry2 (p<0.001), but not that of Spry4. In conclusion, we report for the first time to our knowledge that Spry1 protein is downregulated in human epithelial ovarian cancer. Spry1 expression significantly impacts tumor behavior and shows predictive value as an independent prognostic factor for survival and recurrence.

A correlational study of serum alkaline phosphatase level and developmental mandibular laterognathism

The abnormal cartilage/bone metabolism in unilateral condyle may be a direct factor that contributes to developmental mandibular laterognathism. However, although many molecules have been demonstrated to play crucial roles in the development of temporomandibular joints, the exact molecular mechanisms that lead to the disrupted condylar cartilage/bone development were greatly unknown. In this retrospective study, our findings revealed that serum alkaline phosphatase (ALP) level in adult patients with developmental mandibular laterognathism was lower than that in control subjects, and the serum ALP levels continue to reduce in adult patients (>20 years old). Although the exact relationship between the lower serum ALP level and developmental mandibular laterognathism is unclear, the findings further support the opinion that the condylar growth may sustain for a long time in the affected condyle in patients with developmental mandibular laterognathism and offer an alternative choice to use total serum ALP activity as a possible biomarker to assess condylar growth activity in patients with developmental mandibular laterognathism.

Lubricin protects the temporomandibular joint surfaces from degeneration

The temporomandibular joint (TMJ) is a specialized synovial joint essential for the mobility and function of the mammalian jaw. The TMJ is composed of the mandibular condyle, the glenoid fossa of the temporal bone, and a fibrocartilagenous disc interposed between these bones. A fibrous capsule, lined on the luminal surface by the synovial membrane, links these bones and retains synovial fluid within the cavity. The major component of synovial fluid is lubricin, a glycoprotein encoded by the gene proteoglycan 4 (Prg4), which is synthesized by chondrocytes at the surface of the articular cartilage and by synovial lining cells. We previously showed that in the knee joint, Prg4 is crucial for maintenance of cartilage surfaces and for regulating proliferation of the intimal cells in the synovium. Consequently, the objective of this study was to determine the role of lubricin in the maintenance of the TMJ. We found that mice lacking lubricin have a normal TMJ at birth, but develop degeneration resembling TMJ osteoarthritis by 2 months, increasing in severity over time. Disease progression in Prg4^−/− mice results in synovial hyperplasia, deterioration of cartilage in the condyle, disc and fossa with an increase in chondrocyte number and their redistribution in clusters with loss of superficial zone chondrocytes. All articular surfaces of the joint had a prominent layer of protein deposition. Compared to the knee joint, the osteoarthritis-like phenotype was more severe and manifested earlier in the TMJ. Taken together, the lack of lubricin in the TMJ causes osteoarthritis-like degeneration that affects the articular cartilage as well as the integrity of multiple joint tissues. Our results provide the first molecular evidence of the role of lubricin in the TMJ and suggest that Prg4^−/− mice might provide a valuable new animal model for the study of the early events of TMJ osteoarthritis.

BMPRIA mediated signaling is essential for temporomandibular joint development in mice

The central importance of BMP signaling in the development and homeostasis of synovial joint of appendicular skeleton has been well documented, but its role in the development of temporomandibular joint (TMJ), also classified as a synovial joint, remains completely unknown. In this study, we investigated the function of BMPRIA mediated signaling in TMJ development in mice by transgenic loss-of- and gain-of-function approaches. We found that BMPRIA is expressed in the cranial neural crest (CNC)-derived developing condyle and glenoid fossa, major components of TMJ, as well as the interzone mesenchymal cells. Wnt1-Cre mediated tissue specific inactivation of BmprIa in CNC lineage led to defective TMJ development, including failure of articular disc separation from a hypoplastic condyle, persistence of interzone cells, and failed formation of a functional fibrocartilage layer on the articular surface of the glenoid fossa and condyle, which could be at least partially attributed to the down-regulation of Ihh in the developing condyle and inhibition of apoptosis in the interzone. On the other hand, augmented BMPRIA signaling by Wnt1-Cre driven expression of a constitutively active form of BmprIa (caBmprIa) inhibited osteogenesis of the glenoid fossa and converted the condylar primordium from secondary cartilage to primary cartilage associated with ectopic activation of Smad-dependent pathway but inhibition of JNK pathway, leading to TMJ agenesis. Our results present unambiguous evidence for an essential role of finely tuned BMPRIA mediated signaling in TMJ development.

Analysis by Light, Scanning, and Transmission Microscopy of the Intima Synovial of the Temporomandibular Joint of Human Fetuses during the Development

Objective. To characterize morphologically and ultrastructurally using light microscopy, the scanning electron microscopy and transmission electron microscopy the intima synovial of the temporomandibular joint (TMJ) of human fetuses between the 10th and the 38th week of development. Materials and Methods. The TMJ was dissected bilaterally in 37 human fetuses belonging to the Institute of Embryology of the University Complutense of Madrid and of the Federal University of São Paulo. Results. The outcome by light microscopy showed the morphology of the TMJ and that the formation of inferior joint cavity precedes the superior joint cavity and the presence of blood vessels in the synovial. Conclusion. By scanning and transmission electron microscopy we observed the presence of two well-defined cell types in the intima layer of synovial of the TMJ of human fetuses, macrophage-like type A cell and fibroblast-like type B cell, and the presence of the a third cell type, defined by the name of intermediate lining cell in the intima layer of the synovial.

Interaction between Foxc1 and Fgf8 during mammalian jaw patterning and in the pathogenesis of syngnathia

Syngnathia (bony fusion of the upper and lower jaw) is a rare human congenital condition, with fewer than sixty cases reported in the literature. Syngnathia typically presents as part of a complex syndrome comprising widespread oral and maxillofacial anomalies, but it can also occur in isolation. Most cartilage, bone, and connective tissue of the head and face is derived from neural crest cells. Hence, congenital craniofacial anomalies are often attributed to defects in neural crest cell formation, survival, migration, or differentiation. The etiology and pathogenesis of syngnathia however remains unknown. Here, we report that Foxc1 null embryos display bony syngnathia together with defects in maxillary and mandibular structures, and agenesis of the temporomandibular joint (TMJ). In the absence of Foxc1, neural crest cell derived osteogenic patterning is affected, as osteoblasts develop ectopically in the maxillary prominence and fuse with the dentary bone. Furthermore, we observed that the craniofacial musculature is also perturbed in Foxc1 null mice, which highlights the complex tissue interactions required for proper jaw development. We present evidence that Foxc1 and Fgf8 genetically interact and that Fgf8 dosage is associated with variation in the syngnathic phenotype. Together our data demonstrates that Foxc1 – Fgf8 signaling regulates mammalian jaw patterning and provides a mechanistic basis for the pathogenesis of syngnathia. Furthermore, our work provides a framework for understanding jaw patterning and the etiology of other congenital craniofacial anomalies, including temporomandibular joint agenesis.

Approximately one-third of all babies born with congenital defects, exhibit malformations of the head and face. Anomalies can include cleft lip, cleft palate, and abnormal development of bones and muscles. Such defects result in significant infant mortality, as well as life-long physical and social consequences for patients. Improved repair and the development of prevention strategies requires a thorough understanding of the underlying genetic, molecular, and environmental factors that contribute to normal craniofacial development and the pathogenesis of disease. In this study, we report the first genetic model of syngnathia, a rare human craniofacial defect characterized by bony fusion of the upper and lower jaw. We discovered that Foxc1 is required for normal development of the bones and muscles of the jaw as well as the jaw joint. Our studies provide a mechanistic basis for understanding the cause of human syngnathia as well as the failure of jaw joint formation. Furthermore, our work enhances our knowledge of jaw development and may inform treatment strategies for patients with syngnathia and related craniofacial malformation conditions.

Association between the SPRY1 gene polymorphism and obesity-related traits and osteoporosis in Korean women

BACKGROUND

Emerging evidence has revealed a close relationship between obesity and osteoporosis. It was reported recently that conditional knockout of the Spry1 gene in mice adipocytes causes an increase in body fat and a decrease in bone mass, and that these phenotypes are rescued by Spry1 overexpression in adipose tissue. In this study, we investigated whether genetic variation in the human SPRY1 gene is associated with obesity-related phenotypes and/or osteoporosis in humans.

METHODS

We performed a candidate gene association analysis between the four single nucleotide polymorphisms (SNPs) and 14 imputed SNPs in the SPRY1 gene and obesity-related traits and osteoporosis in a Korean women cohort (3013 subjects).

RESULTS

All four SPRY1 gene SNPs were significantly associated with either obesity-related traits or osteoporosis. The TGCC haplotype in the SRPY1 gene showed simultaneous association with an increased risk for obesity-related traits, percentage body fat (p=0.0087) and percentage abdominal fat (p=0.047), and osteoporosis (odds ratio=1.50; p=0.025) in the recessive genetic model.

CONCLUSIONS

Our results support a previous finding in conditional Spry1 gene knockout mice and suggest that the SPRY1 gene is an important genetic factor for determining the risk of both obesity and osteoporosis in humans.

Muenke syndrome mutation, FgfR3P²⁴⁴R, causes TMJ defects

Muenke syndrome is characterized by various craniofacial deformities and is caused by an autosomal-dominant activating mutation in fibroblast growth factor receptor 3 (FGFR3(P250R) ). Here, using mice carrying a corresponding mutation (FgfR3(P244R) ), we determined whether the mutation affects temporomandibular joint (TMJ) development and growth. In situ hybridization showed that FgfR3 was expressed in condylar chondroprogenitors and maturing chondrocytes that also expressed the Indian hedgehog (Ihh) receptor and transcriptional target Patched 1(Ptch1). In FgfR3(P244R) mutants, the condyles displayed reduced levels of Ihh expression, H4C-positive proliferating chondroprogenitors, and collagen type II- and type X-expressing chondrocytes. Primary bone spongiosa formation was also disturbed and was accompanied by increased osteoclastic activity and reduced trabecular bone formation. Treatment of wild-type condylar explants with recombinant FGF2/FGF9 decreased Ptch1 and PTHrP expression in superficial/polymorphic layers and proliferation in chondroprogenitors. We also observed early degenerative changes of condylar articular cartilage, abnormal development of the articular eminence/glenoid fossa in the TMJ, and fusion of the articular disc. Analysis of our data indicates that the activating FgfR3(P244R) mutation disturbs TMJ developmental processes, likely by reducing hedgehog signaling and endochondral ossification. We suggest that a balance between FGF and hedgehog signaling pathways is critical for the integrity of TMJ development and for the maintenance of cellular organization.