Noggin is required for early development of murine upper incisors

BMP signaling plays crucial roles in the development of many organs, including the tooth. Equally important is BMP signaling homeostasis, as demonstrated by multiple organ defects in mice lacking the extracellular BMP antagonist Noggin. Here, we show that Noggin is initially expressed in the maxillary mesenchyme adjunct to the upper incisor at the initiation stage, and then in the developing teeth, including incisors and molars, from the bud stage. Noggin mutants develop normal molars and mandibular incisors, but form a single, medially located upper incisor that is arrested at the late bud stage. Histological and molecular marker analyses demonstrated that two distinct upper incisor placodes initiate independently at E11.5, but begin to fuse at E12.5, coupling with elevated cell proliferation rates in the developing tooth germs. We further found that Chordin and Gremlin, two other BMP antagonists, are co-expressed with Noggin in the developing lower incisor and molar teeth. These observations indicate the importance of BMP signaling homeostasis, and suggest a functional redundancy between BMP antagonists during tooth development.     

Early morphogenesis of heterodont dentition in minipigs

The minipig provides an excellent experimental model for tooth morphogenesis because its diphyodont and heterodont dentition resemble that of humans. However, little information is available on the processes of tooth development in the pig. The purpose of this study was to classify the early stages of odontogenesis in minipigs from the initiation of deciduous dentition to the late bell stage when the successional dental lamina begins to develop. To analyze the initiation of teeth anlagens and the structural changes of dental lamina, a three-dimensional (3D) analysis was performed. At the earliest stage, 3D reconstruction revealed a continuous dental lamina along the length of the jaw. Later, the dental lamina exhibited remarkable differences in depth, and the interdental lamina was shorter. The dental lamina grew into the mesenchyme in the lingual direction, and its inclined growth was underlined by asymmetrical cell proliferation. After the primary tooth germ reached the late bell stage, the dental lamina began to disintegrate and fragmentize. Some cells disappeared during the process of lamina degradation, while others remained in small islands known as epithelial pearls. The minipig can therefore, inter alia, be used as a model organism to study the fate of epithelial pearls from their initiation to their contribution to pathological structures, primarily because of the clinical significance of these epithelial rests.     

Hamartomatous proliferations of odontogenic epithelium within the jaws: a potential histogenetic source of intraosseous epithelial odontogenic tumors

BACKGROUND: The jawbone is replete with a vestige of odontogenesis. The overall consensus is that intraosseous remnants of the enamel organ and dental lamina are the only histogenetic option for central epithelial odontogenic tumors. Curiously, incipient tumors or possible precursor conditions of residual odontogenic epithelium have rarely been reported in the literature. METHODS: We microscopically evaluated 39,660 biopsy samples to determine the presence of a tumor-like odontogenic epithelial nodule in the maxilla and mandible. RESULTS: Seven intraosseous specimens that associated with a focal proliferation of odontogenic epithelium were retrieved. Six hamartomatous processes showed four different morphologic patterns comparable with the tumor nests comprising ameloblastoma (n = 1), squamous odontogenic tumor (n=1), calcifying epithelial odontogenic tumor (n=2) and calcifying cystic odontogenic tumor (n=2). Among six lesions, four were the intrafollicular development. The remaining case of interest was multiple hyperplastic clear rests of Malassez in association with an impacted tooth. CONCLUSION: Although it is impossible to predict the fate of these microscopic structures of hamartomatous character, the present case series indicates that any of the dormant embryonic residues of odontogenic epithelium can return to an active state, capable of non-reactive, probably neoplastic proliferation of pathological significance.     

Primordial odontogenic tumor: Subepithelial expression of Syndecan‐1 and Ki‐67 suggests origin during early odontogenesis

Primordial odontogenic tumor (POT) is composed of variably cellular myxoid connective tissue, surrounded by cuboidal to columnar odontogenic epithelium resembling the inner epithelium of the enamel organ, which often invaginates into the underlying connective tissue. The tumor is delimited at least partially by a thin fibrous capsule. It derives from the early stages of tooth development. Syndecan‐1 is a heparan sulfate proteoglycan that has a physiological role in several cellular functions, including maintenance of the epithelial architecture, cell‐to‐cell adhesion and interaction of cells with extracellular matrix, and with diverse growth factors, stimulating cell proliferation. Ki‐67 is considered the gold standard as a cell proliferation marker. The aim of this study was to examine the expression of Syndecan‐1 and Ki‐67 proliferation index in POT and normal tooth germs to better understand the biological behavior of this tumor. Results showed that Syndecan‐1 was more intensely expressed in subepithelial mesenchymal areas of POT, in a pattern that resembles the early stages of tooth development. The cell proliferation index (4.1%) suggests that POT is a slow growing tumor. Syndecan‐1 expression in tooth germs in late cap and early bell stages was similar to POT, showing immunopositivity in subepithelial mesenchymal condensed areas. The immunohistochemical findings showed a pattern in which the population of subepithelial mesenchymal cells exhibited greater proliferative activity than the central portion of the dental papilla.     

Notch1在小鼠下颌第一磨牙牙胚发育中的表达

目的探讨Notch1在小鼠下颌第一磨牙胚胎发育过程中的组织学分布。方法制作ICR小鼠下颌第一磨牙不同发育阶段的冰冻组织切片,对小鼠下颌第一磨牙自牙胚发育起始期至出生后2天不同发育阶段组织的Notch1分布情况进行免疫组织化学染色。结果 Notch1在小鼠下颌第一磨牙牙胚发育起始期和蕾状期牙板上皮上方或其包绕的口腔上皮中表达,在牙板上皮中没有表达。自帽状期至钟状期,Notch1在牙胚的中间层表达,而在内釉上皮中无表达。至牙釉质和牙本质分泌期,Notch1仍在颈环部位的中间层表达。此外,Notch1还在牙胚发育不同时期的间充质、牙乳头和早期牙髓中表达。结论 Notch1可能在小鼠下颌第一磨牙发育过程中的牙上皮特别是内釉上皮的细胞分化,以及牙囊和牙乳头细胞分化及分化完成后的牙髓干细胞的稳定性方面有重要作用。     

An immunohistochemical study of odontogenic mixed tumours

Five cases of odontogenic mixed tumour comprising of an ameloblastic fibroma, an adenomatoid odontogenic tumour, an odonto-ameloblastoma and two ameloblastic fibro-odontomas were immunohistochemically investigated. Odontogenic epithelial cells were fully positive for cytokeratin detected by antibody KL-1, although there were some differences in its intensity. In contrast, for tenascin, only immature dental papilla-like mesenchymal tissue, especially around the dental lamina-like odontogenic epithelium, was positive, while the myxomatous area and connective tissue were negative. Positive vimentin staining was observed in some areas of immature dental papilla-like cells as well as the basement membrane of odontogenic epithelium in the ameloblastic fibroma, suggesting that this tumour had developed at the early stage of tooth formation. Proliferating nuclear cell antigen-positive cells were generally rarely seen, but were frequently observed in epithelial cells of the ameloblastic fibroma and odonto-ameloblastoma. These observations suggest that tumour cells in each odontogenic mixed tumour possess characteristic proteins associated with proliferation potential and that ameloblastic fibroma and odonto-ameloblastoma have higher proliferation potential among the tumours examined.     

Embryogenesis of the gingival cyst

The embryogenesis of gingival cysts derived from the dental lamina was studied histologically in paraffin prepared sections of 10 pairs of human fetal jaws and in individual celloidin sections of human fetal skulls. Cystic degeneration in the dental lamina was noted as early as 10 weeks in utero prior to the separation of the developing tooth bud. Rapid proliferation and growth of such cysts was seen in 15-20 week old embryos during the morphodifferentiation stage of tooth development after fragmentation of the lamina had occurred. Islands, strands and nests of dental lamina epithelium were dispersed into extraosseous locations and demonstrated histomorphologic characteristics similar to odontogenically related epithelium seen in adult gingiva. Dental lamina epithelium appears to have a particular predisposition for cystic degeneration and is probably the source of other neoplasms and hamartomas seen in the gingiva.     

Yes相关蛋白基因在牙发育中的作用

牙发育过程,包括胚胎早期预定成牙部位到发育形成完整的牙及牙周组织的发育成熟,是一个复杂的连续过程。牙发育实际上是牙源性上皮与脑神经嵴来源的牙源性间充质之间相互作用的结果,这一过程受到诸多信号的影响。Yes相关蛋白基因（YAP）是Hippo通路中的靶基因,在牙胚发育的初始阶段,可在不同部位检测到其表达。Hippo-YAP信号通路通过抑制YAP的活性,调控细胞增生和程序性细胞死亡间的平衡,从而调控器官的大小。本文就Hippo-YAP信号通路和YAP在牙发育过程中的表达等研究进展作一综述。     

Expression and roles of CCN2 in dental mesenchymal cells in primary culture—With findings in a case of odontogenic myxofibroma

Purpose of the researchTooth germ development involves multiple events, including cell proliferation and cell differentiation. Connective tissue growth factor (CTGF/CCN2) is a signaling protein involved in tooth germ development, and we investigated how it is expressed and what roles it may have in primary cultures of mesenchymal cells derived from the developing tooth germ. We also examined the expression of CCN2 in a human odontogenic myxofibroma, a benign tumor of odontogenic mesenchymal origin, and considered the possible roles of CCN2 in the development of myxofibromas.Materials and methodsMesenchymal cells of early bell-stage tooth germs were isolated from Day-90 bovine embryos and placed in primary culture. A resected specimen from a patient with odontogenic myxofibroma was prepared for immunohistochemical studies.Principal resultsThe CCN2 expression level in proliferating odontogenic mesenchymal cells freshly isolated from the early bell stage of developing bovine tooth germs and placed in primary culture was 3 times higher than that in the confluent non-proliferating cells. Recombinant CCN2 significantly increased the proliferation and type I collagen expression in odontogenic mesenchymal cells in primary culture. Immunohistochemical analysis on myxofibroma case revealed that CCN2 was detectable in MIB-1, a cellular marker of proliferation-positive odontogenic mesenchymal cells adjacent to capillary blood vessels and in the endothelial cells of the vessels in the tumor.Major conclusionCCN2 signaling would influence the proliferation of and extracellular matrix production by dental mesenchymal cells. Our results suggest that the same mechanisms of CCN2 action toward dental mesenchymal cells would also be operative in the odontogenic myxofibroma microenvironment.     

Dental lamina as presumptive source of odontogenic cyst

The possibility of the dental lamina as a source of odontogenic cyst was investigated. The mandibular first molar tooth germs with the dental lamina and surface oral epithelium were cut from 17.5-day-old C3H mouse embryos. The following 5 kinds of grafts were prepared: (I) recombinant of the dental lamina and dental papilla, (II) dental lamina, (III) dental papilla, (IV) recombinant of the oral epithelium and dental papilla and (V) oral epithelium. After the renal subcapsular transplantation to the 3-month-old syngenic male mice, each graft was harvested at timed sequences from 2 to 24 weeks and was examined histopathologically. The recombinant of the dental lamina and dental papilla (1) grew into a cyst lined by para-keratinized stratified squamous epithelium. The cyst enlarged gradually and might be compared to the odontogenic keratocyst of the human being. The recombinant of the oral epithelium and dental papilla (IV) and the oral epithelium (V) developed into a cyst lined by orthokeratinized stratified squamous epithelium which differed from the epithelium seen in Experiment (I). The dental papilla (III) grew to be a bone tissue while nothing developed from the dental lamina (II). These results suggest that the dental lamina is one of the sources of the odontogenic keratocyst and the dental papilla plays an important role in its histogenesis.     

Stem Cell Regulatory Gene Expression in Human Adult Dental Pulp and Periodontal Ligament Cells Undergoing Odontogenic/Osteogenic Differentiation

IntroductionDuring development and regeneration, odontogenesis and osteogenesis are initiated by a cascade of signals driven by several master regulatory genes.MethodsIn this study, we investigated the differential expression of 84 stem cell–related genes in dental pulp cells (DPCs) and periodontal ligament cells (PDLCs) undergoing odontogenic/osteogenic differentiation.ResultsOur results showed that, although there was considerable overlap, certain genes had more differential expression in PDLCs than in DPCs. CCND2, DLL1, and MME were the major upregulated genes in both PDLCs and DPCs, whereas KRT15 was the only gene significantly downregulated in PDLCs and DPCs in both odontogenic and osteogenic differentiation. Interestingly, a large number of regulatory genes in odontogenic and osteogenic differentiation interact or crosstalk via Notch, Wnt, transforming growth factor β (TGF-β)/bone morphogenic protein (BMP), and cadherin signaling pathways, such as the regulation of APC, DLL1, CCND2, BMP2, and CDH1. Using a rat dental pulp and periodontal defect model, the expression and distribution of both BMP2 and CDH1 have been verified for their spatial localization in dental pulp and periodontal tissue regeneration.ConclusionsThis study has generated an overview of stem cell–related gene expression in DPCs and PDLCs during odontogenic/osteogenic differentiation and revealed that these genes may interact through the Notch, Wnt, TGF-β/BMP, and cadherin signaling pathways to play a crucial role in determining the fate of dental derived cell and dental tissue regeneration. These findings provided a new insight into the molecular mechanisms of the dental tissue mineralization and regeneration.     

The pathogenesis of odontogenic cysts: a review

The pathogenesis of the three common forms of odontogenic cyst is discussed. It is concluded that the dental cyst arises from proliferation of the epithelial rests of Malassez in a focus of inflammation stimulated by pulpal necrosis of the associated tooth. It enlarges by unicentric expansion from the hydrostatic pressure of its contents. The dentigerous cyst arises from pooling of inflammatory exudate, which is derived from the obstructed follicular veins of an unerupted tooth and accumulates between the reduced enamel epithelium and the crown of the tooth. It enlarges by unicentric expansion from the hydrostatic pressure of its contents. The odontogenic keratocyst arises by proliferation of the residues of the dental lamina, possibly as a hamartomatous abnormality. It enlarges by both multicentric expansion due to the proliferation of localized groups of epithelial cells in the lining and by unicentric expansion from the hydrostatic pressure of its contents.     

K-Ras gene status and expression of Ras/mitogen-activated protein kinase (MAPK) signaling molecules in ameloblastomas

BACKGROUND: To clarify the roles of rat sarcoma (Ras)/mitogen-activated protein kinase (MAPK) signaling pathway in oncogenesis and cytodifferentiation of odontogenic tumors, K-Ras gene status and expression of Ras, Raf1, MAPK/extracellular signal-regulated kinase (ERK) kinase (MEK)1, and ERK1/2 proteins were analyzed in ameloblastomas as well as in tooth germs. METHODS: Paraffin sections of 10 tooth germs and 46 benign and 6 malignant ameloblastomas were examined immunohistochemically for the expression of K-Ras, Raf1, MEK1, and ERK1/2. Frozen tissue samples of 22 benign ameloblastomas and 1 malignant (metastasizing) ameloblastoma were analyzed by direct DNA sequencing to detect K-Ras gene alteration. RESULTS: Immunohistochemical reactivity for K-Ras, Raf1, MEK1, and ERK1/2 was detected in both normal and neoplastic odontogenic epithelium, and these molecules were reactive chiefly with odontogenic epithelial cells neighboring the basement membrane. Plexiform ameloblastomas showed slightly stronger expression of these Ras/MAPK signaling molecules than follicular ameloblastomas. Keratinizing cells and granular cells showed decreased reactivity for the signaling molecules. Basal cell ameloblastomas showed slightly stronger reactivity for the signaling molecules than did the other subtypes. K-Ras immunoreactivity in malignant ameloblastomas was lower than that in dental lamina of tooth germs. Direct DNA sequencing showed a GGT to GCT point mutation at codon 12 of K-Ras gene in one ameloblastoma. Conclusion: Expression of K-Ras, Raf1, MEK1, and ERK1/2 in tooth germs and ameloblastomas suggests that Ras/MAPK signaling pathway functions to regulate cell proliferation and differentiation in both normal and neoplastic odontogenic epithelium. K-Ras gene status implied that K-Ras mutations might play a minor role in oncogenesis of odontogenic epithelium.     

ADAM28在小鼠牙胚发育中的时空表达

目的:研究ADAM28在小鼠牙胚发育中的时空分布。方法:采用免疫组织化学方法和图像分析技术观察ADAM28在小鼠牙胚发育各期的表达分布及差异。结果:ADAM28在牙胚发育各时期均有不同程度的表达。帽状期开始即在口腔上皮及成釉器星网层细胞、基底膜、牙乳头细胞和牙囊细胞表达强阳性,到钟状晚期,成釉细胞、釉基质、上皮根鞘和牙乳头细胞阳性表达;至冠根硬组织发育期,成釉细胞、成牙本质细胞、上皮根鞘、成牙骨质细胞、牙乳头细胞、牙囊细胞阳性表达。结论:ADAM28作为上皮和间充质间重要的信号分子,参与了从蕾状期到钟状晚期、从基质分泌到硬组织形成的牙冠、牙根形态发生过程,它可能在牙源性间充质细胞的早期形成、增殖与分化启动中发挥重要作用。     

Tooth and jaw: molecular mechanisms of patterning in the first branchial arch

The mammalian jaw apparatus is ultimately derived from the first branchial arch derivatives, the maxillary and mandibular processes, and composed of a highly specialised group of structures. Principle amongst these are the skeletal components of the mandible and maxilla and the teeth of the mature dentition. Integral to the development of these structures are signalling interactions between the stomodeal ectoderm and underlying neural crest-derived ectomesenchymal cells that populate this region. Recent evidence suggests that in the early mouse embryo, regionally restricted expression of homeobox-containing genes, such as members of the Dlx, Lhx and Gsc classes, are responsible for generating early polarity in the first branchial arch and establishing the molecular foundations for patterning of the skeletal elements. Teeth also develop on the first branchial arch and are derived from both ectoderm and the underlying ectomesenchyme. Reciprocal signalling interactions between these cell populations also control the odontogenic developmental programme, from early patterning of the future dental axis to the initiation of tooth development at specific sites within the ectoderm. In particular, members of the Fibroblast growth factor (Fgf), Bmp, Hedgehog and Wnt families of signalling molecules induce regionally restricted expression of downstream target genes in the odontogenic ectomesenchyme. Finally, the processes of morphogenesis and cellular differentiation ultimately generate a tooth of specific class. Many of the same genetic interactions that are involved in early tooth development mediate these effects through the activity of localised signalling centres within the developing tooth germ.     

β-连环蛋白和腺瘤性结肠息肉病蛋白在小鼠牙胚发育中的表达及相互关系的研究

目的观察β-连环蛋白（β-catenin）和腺瘤性结肠息肉病（APC）蛋白在胎鼠下颌第一磨牙牙胚中的表达,探讨两者的作用及相互关系。方法将昆明小鼠按雌雄比2∶1合笼,发现阴栓视为妊娠,定为E0.5 d,制作E13.5 d、E14.5 d、E15.5 d、E16.5 d、E17.5 d胎鼠下颌第一磨牙石蜡切片,免疫组化SP法检测β-catenin和APC蛋白的表达与分布。结果β-catenin在牙胚蕾状期、帽状期、钟状期上皮内均有表达,且随着发育的成熟,其表达逐渐增强,着色于细胞膜、质及核。APC蛋白在蕾状期牙蕾上皮呈强阳性表达,随着牙胚发育其表达逐渐减弱,着色在细胞膜、质。β-catenin与APC蛋白有显著的负相关性（P<0.01）。结论β-catenin表达于牙胚早期细胞核及细胞质内,提示其参与了牙胚早期的细胞增殖过程。β-catenin与APC蛋白的时空表达有重叠现象,并呈显著负相关,这符合WNT经典信号通路中两者的作用关系。     

牙源性角化囊肿发生的实验研究

摘要 目的:探讨牙源性角化囊肿的组织由来。方法:将小鼠胎仔的牙板与牙乳头、口腔粘膜上皮与牙乳头,以及牙胚制成移植片,分别移植到同系成鼠的肾被膜下,定期回收组织片,进行组织病理学观察。结果:发现58例移植片中,41例形成角化囊肿,45例伴有牙体组织形成。结论:实验产生的角化囊肿在组织学上与人的牙源性角化囊肿十分相似,可以为进一步研究该囊肿提供一个较理想的动物模型;证实了牙源性上皮可以发生角化;提示了牙板、口腔粘膜上皮和外釉上皮可能是该囊肿的组织由来之一。