Human ameloblastoma tumors express the amelogenin gene

Amelogenin is a Potential Biomarker for the Aggressiveness in Odontogenic Tumors

Amelogenin (AMEL), the major structural protein of the enamel organic matrix, constitutes more than 90% of the enamel’s protein content, Aberrations of amelogenin are thought to be involved in the oncogenesis of odontogenic epithelium. The expression of amelogenin is possibly an indicator of differentiation of epithelial cells in the odontogenic tumors. Aim of the study: Investigating the expression of amelogenin in some odontogenic tumors, using an anti-amelogenin polyclonal antibody, and then compare it with AMEL expression in tooth buds as control. Materials and Methods: study sample consisted of 10 formalin-fixed, paraffin- embedded specimens of ameloblastoma, 10 Keratocystic odontogenic tumors, and 10 tooth buds were conventionally stained with hematoxylin-eosin and immunohistochemically with AMEL polyclonal antibody. Results: All of the odontogenic tumors expressed AMEL in the epithelial component, Intensity of expression in ameloblastoma and Keratocystic odontogenic tumor was lower, compared with tooth buds, Statistical analysis indicated a significant differences between the tumors and tooth buds. Conclusion: Amelogenin can be used as a marker for odontogenic epithelium, and the expression of amelogenin is possibly an indicator of epithelial cells differentiation in the odontogenic tumors, and therefore in prediction of the histological behavior of odontogenic tumors.

Assessment of quality of life in giant ameloblastoma adolescent patients who have had mandible defects reconstructed with a free fibula flap

Background

The reconstruction of mandibular defects after giant ameloblastoma resection is one of the most challenging problems facing reconstructive surgeons. Mandibular resection has been associated with a poor quality of life (QOL), particularly in adolescent patients reconstructed with a free fibula flap. This study aims to evaluate QOL outcomes in adolescent patients who have had mandibular resections of giant ameloblastoma and reconstruction with a free fibula flap and to collect information about their socio-cultural situation.

Methods

The present study assessed 45 adolescent patients who had undergone immediate mandible reconstruction with a free fibula flap for faint ameloblastoma using University of Washington Quality of Life (UW-QOL) and 14-item Oral Health Impact Profile (OHIP-14) questionnaires.

Results

Thirty-five of the 54 questionnaires were returned (64.81%). In the UW-QOL, of the twelve disease-specific domains, the best three scores from the patients related to pain, shoulder and appearance and the worst three scores related to chewing, anxiety and saliva. In the OHIP-14, the lowest-scoring domain was handicap, followed by physical pain and social disability.

Conclusions

Mandibular reconstruction with a free fibular flap significantly influenced the adolescent patients’ QOL. Adolescent patients pay more attention to postoperative facial appearance; this should be considered in surgical planning.

Current concepts and occurrence of epithelial odontogenic tumors: I. Ameloblastoma and adenomatoid odontogenic tumor

Ameloblastomas and adenomatoid odontogenic tumors (AOTs) are common epithelial tumors of odontogenic origin. Ameloblastomas are clinico-pathologically classified into solid/multicystic, unicystic, desmoplastic, and peripheral types, and also divided into follicular, plexiform, acanthomatous, granular types, etc., based on their histological features. Craniopharyngiomas, derived from the remnants of Rathke's pouch or a misplaced enamel organ, are also comparable to the odontogenic tumors. The malignant transformation of ameloblastomas results in the formation of ameloblastic carcinomas and malignant ameloblastomas depending on cytological dysplasia and metastasis, respectively. AOTs are classified into follicular, extrafollicular, and peripheral types. Ameloblastomas are common, have an aggressive behavior and recurrent course, and are rarely metastatic, while AOTs are hamartomatous benign lesions derived from the complex system of the dental lamina or its remnants. With advances in the elucidation of molecular signaling mechanisms in cells, the cytodifferentiation of epithelial tumor cells in ameloblastomas and AOTs can be identified using different biomarkers. Therefore, it is suggested that comprehensive pathological observation including molecular genetic information can provide a more reliable differential diagnosis for the propagation and prognosis of ameloblastomas and AOTs. This study aimed to review the current concepts of ameloblastomas and AOTs and to discuss their clinico-pathological features relevant to tumorigenesis and prognosis.

Review article: Current concepts of ameloblastoma pathogenesis

Ameloblastoma is a locally destructive and invasive tumour that can recur despite adequate surgical removal. Molecular studies have offered interesting findings regarding ameloblastoma pathogenesis. In the present review, the following topics are discussed regarding its molecular nature: clonality, cell cycle proliferation, apoptosis, tumour suppressor genes, ameloblastin and other enamel matrix proteins, osteoclastic mechanism and matrix metalloproteinases and other signalling molecules. It is clear from the literature reviewed that translational studies are necessary to identify prognostic markers of ameloblastoma behaviour and to establish new diagnostic tools to the differential diagnosis of unicystic from multicystic ameloblastoma. Finally, molecular biology studies are also important to develop more effective alternative approaches to the treatment of this aggressive odontogenic tumour.

Intraosseous ameloblastoma

Ameloblastomas are benign slow-growing aggressive neoplasms with a poorly understood potential for rare metastasis. They are capable of reaching large sizes with extensive local bone erosion and destruction. They are composed of a mixture of ameloblastic epithelium and mesenchyme and arise from rests of outer and inner enamel epithelium and dental lamina. Microscopically, ameloblastomas are recognizable from their recapitulation of embryologic ameloblasts and stellate reticulum. There are 3 subtypes: the conventional or solid-multicystic variant, the unicystic variant, and the desmoplastic variant. Treatment planning for a given tumor includes consideration of location, primary versus recurrent, size, presence of cortical perforation, and age and health of the patient. Complete excision is recommended for conventional and desmoplastic variants. The unicystic variant requires additional subtyping to determine the best treatment approach.

[Maxillary and mandibular carcinogenesis: research and prospects]

Development and growth of odontogenic tumours depend on impairment of numerous genes and molecules. In recent years, most of the genes involved in dental development were identified. This produced a new basis for the study of oral pathology and maxillofacial carcinogenesis. A better understanding of these molecular phenomena should allow to better determine the evolution of such lesions. Research breakthroughs should facilitate the development of new molecular and genetic therapeutic perspectives.

Molecular pathology of odontogenic tumors

Odontogenic tumors are lesions derived from the elements of the tooth-forming apparatus and are found exclusively within the jawbones. This review represents a contemporary outline of our current understanding of the molecular and genetic alterations associated with the development and progression of odontogenic tumors, including oncogenes, tumor-suppressor genes, oncoviruses, growth factors, telomerase, cell cycle regulators, apoptosis-related factors, regulators of tooth development, hard tissue-related proteins, cell adhesion molecules, matrix-degrading proteinases, angiogenic factors, and osteolytic cytokines. It is hoped that better understanding of related molecular mechanisms will help to predict the course of odontogenic tumors and lead to the development of new therapeutic concepts for their management.

Analysis of amelogenin gene (AMGX, AMGY) expression in ameloblastoma

Although the amelogenin gene is expressed in ameloblastoma, the precise expression pattern of X and Y amelogenin genes (AMGX, AMGY) in this tumor has not yet been identified. In this study, we analyzed amelogenin gene expression in 19 samples (9 male, 10 female) of oral ameloblastomas by RT-PCR and detect the chromosomal origin of amelogenin mRNA by restriction enzyme digestion of the RT-PCR product. All tumor samples expressed amelogenin mRNA. We could detect increased level of AMGY expression in all male samples, higher than that of AMEX. It is an interesting finding as in normal male tooth development, the expression of AMGY is very much lower than that of AMGX. We postulate that epigenetic change of sex chromosomes may have some correlations with tumorigenesis of ameloblastoma. We also discuss the other possible mechanisms and points for future studies on this change in expression pattern.

Ameloblastin is a cell adhesion molecule required for maintaining the differentiation state of ameloblasts

Tooth morphogenesis results from reciprocal interactions between oral epithelium and ectomesenchyme culminating in the formation of mineralized tissues, enamel, and dentin. During this process, epithelial cells differentiate into enamel-secreting ameloblasts. Ameloblastin, an enamel matrix protein, is expressed by differentiating ameloblasts. Here, we report the creation of ameloblastin-null mice, which developed severe enamel hypoplasia. In mutant tooth, the dental epithelium differentiated into enamel-secreting ameloblasts, but the cells were detached from the matrix and subsequently lost cell polarity, resumed proliferation, and formed multicell layers. Expression of Msx2, p27, and p75 were deregulated in mutant ameloblasts, the phenotypes of which were reversed to undifferentiated epithelium. We found that recombinant ameloblastin adhered specifically to ameloblasts and inhibited cell proliferation. The mutant mice developed an odontogenic tumor of dental epithelium origin. Thus, ameloblastin is a cell adhesion molecule essential for amelogenesis, and it plays a role in maintaining the differentiation state of secretory stage ameloblasts by binding to ameloblasts and inhibiting proliferation.

Allelic loss of tumor suppressor genes in ameloblastic tumors

Ameloblastoma is an odontogenic tumor with a variety of histologic appearances and an unpredictable biologic behavior. Little is known about allelic losses of tumor suppressor genes in ameloblastomas. This study surveyed DNA damage in ameloblastomas and correlated this with histologic sub-type and clinical outcome. There were 12 ameloblastomas (two peripheral, eight solid, and two unicystic) and three ameloblastic carcinoma studied for loss of heterozygosity of tumor suppressor genes on chromosomes 1p, 3p, 9p,10q, and 17p (L-myc, hOGG1, p16, pten, and p53). The frequency of allelic loss and the intratumoral heterogeneity were calculated. L-myc (71% frequency of allelic loss) and pten (62% frequency of allelic loss) had the most frequent allelic losses. Overall frequency of allelic loss and intratumoral heterogeneity were higher in mandibular and in unicystic tumors and lower in tumors that recurred/metastasized. The rate of allelic loss in the three carcinomas was similar to that seen in benign tumors. The frequency of allelic loss and intratumoral heterogeneity did not correlate with age, gender, histologic subtype, or prognosis. Since tumors that behaved aggressively did not harbor more allelic losses, it is likely that DNA damage in ameloblastomas and ameloblastic carcinomas is sporadic and cumulative. We conclude that other genetic or epigenetic mechanisms may be responsible for malignant behavior in ameloblastic carcinomas.

mRNA expression and phenotype of odontogenic tumours in the v-Ha-ras transgenic mouse

Ameloblastomas are the most common odontogenic neoplasia in humans, and although typically considered locally invasive and benign, frequently recur subsequent to surgical resection. The Tg.AC transgenic mouse carrying the v-Ha-ras oncogene has been found to spontaneously develop ameloblastoma-like tumours (35% by 1 year of age) that are rare in the wild type FVB background strain.

OBJECTIVE

The purpose of this study was to characterise the mRNA expression of genes in the mouse tumours that are either expressed in human ameloblastomas or essential for normal odontogenesis and to correlate the expression to the histological phenotype.

STUDY METHODS

Histological, immunohistochemical and RT-PCR studies were used to evaluate clinically demonstrable odontogenic tumours occurring spontaneously in seven Tg.AC v-Ha-ras transgenic mice (homozygous, at 7 months of age or heterozygous at 11 months of age).

RESULTS

Most genes profiled were expressed in all tumour samples, however three (amelogenin, matrix metalloproteinase-20 (MMP-20) and Dlx7) displayed differential expression. In addition, only the most highly differentiated tumour stained positively for collagen. In most cases, the variable expression could be explained by reference to the histological phenotype, although differences in gene expression were apparent within the Type 2 and the mixed phenotype tumours.

CONCLUSIONS

These data confirm that many of the genes thought to be important in odontogenesis and odontogenic tumour formation in humans are also expressed in these murine ameloblastoma-like tumours however genes associated with terminal differentiation of ameloblasts demonstrate differential expression between the tumour phenotypes.

Intragenomic conflict and cancer

Intragenomic conflict occurs when some elements within the genome produce effects that enhance their own probability of replication or transmission at the expense of other elements within the same genome. Here it is proposed that mutations involved in intragenomic conflict are particularly likely to be co-opted by evolving lineages of cancer cells, and hence should be associated with the occurrence of cancer. We discuss several types of intragenomic conflict that are associated with various forms of cancer.

Clear cell odontogenic carcinoma. Report of two cases and review of the literature

This study reviews the literature and reports on the morphologic and immunophenotypic features of 2 clear cell odontogenic carcinomas occurring in the mandible of elderly women, showing extensive infiltration into adjacent tissues. The tumor cells were large, with clear cytoplasm, and arranged in irregular sheets. Some of the latter demonstrated a peripheral rim of cells with eosinophilic cytoplasm or included duct-like structures. There was no evidence of ameloblastic differentiation. Most cells contained glycogen granules and were immunoreactive for cytokeratins and epithelial membrane antigen. In the differential diagnosis other clear cell odontogenic, salivary gland, and metastatic tumors should be considered. Both cases were treated with surgical excision, and the patients are free of disease after 3 and 5 years, respectively. In the literature, however, variable behavior of these tumors has been reported, including recurrence and metastases. It is recommended that terms such as clear cell ameloblastoma and clear cell odontogenic tumor not be used to describe such tumors.

Use of calretinin in the differential diagnosis of unicystic ameloblastomas

AIMS

Calretinin, a 29-kDa calcium-binding protein is expressed widely in normal human tissues and tumours including both unicystic and solid and multicystic ameloblastomas. The histological distinction between unicystic ameloblastomas and certain non-neoplastic odontogenic cysts can be problematic. The objective of this study was to determine whether calretinin was expressed in the lining epithelium of odontogenic keratocysts, residual and dentigerous cysts and to determine whether this calcium-binding protein could be used to distinguish these cysts from the unicystic ameloblastoma.

METHODS AND RESULTS

The lining epithelium in 22 cases of odontogenic keratocyst, 26 cases of residual cyst and 20 cases of dentigerous cyst were examined for the expression of calretinin. No positive epithelial staining was observed in any of these cystic lesions. In comparison, however, 81.5% of cases of unicystic ameloblastoma showed a coarse dark brown staining of the more superficial epithelial cell layers. Scattered positive stromal and epithelial cells were present; these were interpreted as mast cells.

CONCLUSIONS

Calretinin appears to be a specific immunohistochemical marker for neoplastic ameloblastic epithelium and we suggest that it may be an important diagnostic aid in the differential diagnosis of cystic odontogenic lesions and ameloblastic tumours.

Tuftelin mRNA is expressed in a human ameloblastoma tumor

RT-PCR, Southern blotting and DNA sequencing have established for the first time that tuftelin mRNA is expressed in human ameloblastoma tumor. The expression of amelogenin mRNA in ameloblastoma was also established, confirming earlier reports by Snead et al. These results corroborate, on a molecular level, the enamel organ epithelial origin of ameloblastoma. In view of the present results, it is interesting that previous studies have indicated that although ameloblastoma, a non-mineralized odontogenic tumor, transcribes amelogenin mRNA, amelogenin (and enamelin) proteins are not expressed in this tissue. However, in mineralizing odontogenic tumors, both these classes of proteins are expressed.

Cloning and characterization of the human ameloblastin gene

We isolated the full-length human ameloblastin (AMBN) cDNA clone using reverse transcription-polymerase chain reaction (RT-PCR) methods. Sequence analysis of the AMBN cDNA revealed an open reading frame of 1341bp encoding a 447-amino-acid protein. Comparison with pig, cattle, rat, and mouse AMBN sequences showed a high amino acid sequence similarity and led to the identification of a novel 78bp (26 amino acids) insert resulting from internal sequence duplication. By DNA analysis of a human genomic clones, the AMBN gene was shown to consist of 13 exons and a novel 78bp segment, which proved to comprise two small exons. Human ameloblastomas express AMBN transcripts that contain some mutations.

Immunohistochemical detection and distribution of enamelysin (MMP-20) in human odontogenic tumors

Enamelysin is a tooth-specific protease that was initially isolated from porcine enamel organ and subsequently from human odontoblasts. Since this protease is thought to play important roles in tooth development, the evaluation of enamelysin in odontogenic tumors may aid our understanding of the histogenesis and cell differentiation of such lesions. A monoclonal antibody (203-1C7) was generated against synthesized human enamelysin oligopeptide and was used to assess the immunolocalization of enamelysin in healthy developing tooth germs and various types of odontogenic lesions. In tooth germs, enamelysin expression was detected only in the secretory enamel. Thus, 203-1C7 may serve as an enamel-specific marker in the late stage of enamel matrix development and calcification. In odontogenic lesions, strong enamelysin staining was demonstrated in the immature enamel matrix of ameloblastic fibro-odontomas and odontomas. Furthermore, enamelysin was also detected in globular amyloid masses and calcified foci in calcifying epithelial odontogenic tumors, hyaline droplets, small and large mineralized areas in adenomatoid odontogenic tumors, and a portion of ghost cells in calcifying odontogenic cysts. Positive reactivity was also observed in selected tumor cells in some of these tumors. No intracellular staining for enamelysin was detected in ameloblastomas or the ameloblastic portion of ameloblastic fibro-odontomas. Also, enamelysin was not detected in dentin, dysplastic dentinoid hyaline matrices, and cementum that were present within the tumors examined. Thus, taken together, our results suggest that the enamelysin-specific monoclonal antibody (203-1C7) may be utilized as a marker of early enamel development and that enamelysin may be involved in the pathogenesis of specific odontogenic tumors.

Aberrant gene expression in epithelial cells of mixed odontogenic tumors

Comparative investigations of odontogenic cells in normally forming teeth and tumors may provide insights into the mechanisms of the differentiation process. The present study is devoted to late phenotypic markers of ameloblast and odontoblast cells, i.e., proteins involved in biomineralization. The in situ expression of amelogenins, keratins, collagens type III and IV, vimentin, fibronectin, osteonectin, and osteocalcin was performed on normal and tumor odontogenic human cells. The pattern of protein expression showed some similarities between ameloblasts and odontoblasts present in normally developing human teeth and cells present in neoplastic tissues of ameloblastic fibroma, ameloblastic fibro-odontomas, and complex odontomas. Amelogenins (for ameloblasts) and osteocalcin (for odontoblasts) were detected in cells with well-organized enamel and dentin, respectively. In contrast, "mixed" cells located in epithelial zones of mixed odontogenic tumors co-expressed amelogenins and osteocalcin, as shown by immunostaining. The presence of osteocalcin transcripts was also demonstrated by in situ hybridization in these cells. Keratins and vimentin were detected in the same epithelial zones. Tumor epithelial cells were associated with various amounts of polymorphic matrix (amelogenin- and osteocalcin-immunoreactive), depending on the types of mixed tumors. No osteocalcin labeling was found in epithelial tumors. This study confirms that the differentiation of normal and tumor odontogenic cells is accompanied by the expression of some common molecules. Furthermore, the gene products present in normal mesenchymal cells were also shown in odontogenic tumor epithelium. These data may be related to a tumor-specific overexpression of the corresponding genes transcribed at an undetectable level during normal development and/or to an epithelial-mesenchymal transition proposed to occur during normal root formation. A plausible explanation for the results is that the odontogenic tumor epithelial cells are recapitulating genetic programs expressed during normal odontogenesis, but the tumor cells demonstrate abnormal expression patterns for these genes.

Amelogenin expression in canine oral tissues and lesions

Amelogenins are major enamel proteins within the enamel extracellular matrix. The expression of amelogenin was confirmed in neonatal tissues of the canine jaw. The sequence of a portion of canine amelogenin cDNA, within exons 5 and 6, was determined and found to be closely homologous to sequences reported in the cow, pig, mouse and human being. Two acanthomatous epulides collected from clinically affected dogs showed amelogenin expression, whereas 22 other canine oral lesions, including six additional acanthomatous epulides, did not show amelogenin expression. Examination of structural proteins may allow precise identification of the histogenesis of the odontogenic neoplasms, which are often difficult to distinguish by means of morphological criteria alone.

Establishment of ameloblastoma cell line, AM-1

Ameloblastomas are slowly growing, locally invasive neoplasms with a potentially destructive behaviour. The molecular mechanisms that regulate the cell growth and invasion of ameloblastoma cells are unknown. Because ameloblastoma cells placed in culture have a very limited lifespan, the establishment of immortalized clones of ameloblastoma cells would aid its study. We produced an immortalized ameloblastoma cell line (AM-1) using human papillomavirus type-16. This cell line maintains epithelial cell morphology and expresses cytokeratins K8, K14, K18, K19. Furthermore, bcl-2 protein, which prevents apoptosis, is expressed. We investigated the behaviour of these cells on a collagen matrix in vitro. These cells grew in a monolayer over foci of collagen degradation and could invade the collagen gel at such sites. Since the behavior of cell line AM-1 mimics the behavior of ameloblastoma in vivo, it may be a valuable model for the study of these neoplasms.

Production of amelogenin by enamel epithelium of Hertwig's root sheath

OBJECTIVE

To study the multiple potentials of differentiating odontogenic epithelial cells.

STUDY DESIGN

Bilateral first and second maxillary molars of 30 immature rats were perforated into the pulp chambers with a round bur. The pulps were observed histologically and immunohistochemically for amelogenin 3, 7, and 14 days after the perforation.

RESULTS

On day 7, the enamel epithelium of Hertwig's root sheath migrated and formed oval-shaped epithelial islands that resembled epithelial rests of Malassez. On day 14, the islands consisted of epithelial cells with large nuclei and cytoplasm partially surrounded by a subsequently formed osteodentin and cementum. Immunoreactivity for amelogenin was observed in the large epithelial cells and in the area between the cells as well as the calcified tissues. Some of the enamel epithelium resembling columnar ameloblasts of the enamel organ were also positive for amelogenin.

CONCLUSIONS

The enamel epithelium of Hertwig's root sheath appeared to differentiate into ameloblasts and produce amelogenin.

Clear cell ameloblastoma or odontogenic carcinoma. A case report

An ameloblastoma of the right maxilla with a biphasic pattern of folicular ameloblastoma and clear cells, with an aggressive clinical behaviour in a 71-year-old male is reported. A literature review of clear cell ameloblastomas is made, focussing the discussion on the convenience of considering this type of ameloblastoma to be a low-grade odontogenic carcinoma.

Embryonic growth and the evolution of the mammalian Y chromosome. II. Suppression of selfish Y-linked growth factors may explain escape from X-inactivation and rapid evolution of Sry

The mammalian Y chromosome may be an attractor for selfish growth factors. A suppressor of the selfish growth effects would be expected to spread were it to have an appropriate parent-specific expression rule. A suppressor could act by boosting the resource demands of competing female embryos. This possibility may explain incidences of the escape from X-inactivation and provides a rationale for why these genes typically have Y-linked homologues. Alternatively, a suppressor could act to decrease the resource demands of males with the selfish Y. This possibility is supported by the finding that the size of male, but not female, human infants is negatively correlated to the number of X chromosomes. A protracted arms race between a selfish gene and its suppressor may ensue. Both the variation in copy number of Zfy and the unusually fast sequence evolution of Sry may be explained by such an arms race. As required by the model, human Sry is known to have an X-linked suppressor. Preliminary evidence suggests that, as predicted, rapid sequence evolution of Sry may be correlated with female promiscuity. The case for fast sequence evolution as the product of maternal/foetal conflict is strengthened by consideration of the rapid evolution of placental lactogens in both ruminants and rodents.

Polyoma virus-induced murine odontogenic tumors

Neonatal mouse pups were injected subcutaneously with polyoma virus to induce odontogenic tumors. This treatment resulted in a spectrum of tumors that arose in organs dependent upon epithelial-mesenchymal interactions for their organogenesis, which included the teeth, salivary glands, thymus, and lacrimal glands. In addition, several odontogenic tumors with a histologic resemblance to ameloblastoma were identified and analyzed with respect to the presence of markers specific for various stages of ameloblast differentiation. Immunodetection analyses of the odontogenic tumors identified fibronectin and laminin, typical of basement membrane organization during early tooth organogenesis. These same tumors failed to express amelogenin, a gene whose expression is limited to differentiated ameloblasts. In contrast, a 47 kDa enamelin-like polypeptide was identified with the use of an antienamelin antibody. These data were interpreted to suggest that the polyoma virus truncated the differentiation pathway for these odontogenic tissues at an early stage of their development and retained the expression of basement membrane components and the enamelin-like polypeptides, yet excluded expression of amelogenin gene products. This observation suggests that polyoma viral transformation may dysregulate odontogenic tissue interactions and produce tumors composed of cells arrested at a specific stage in their development.

Maintenance of amelogenin gene expression by transformed epithelial cells of mouse enamel organ

Electroporation was used to introduce foreign genes into cells derived from the mouse enamel organ epithelia (EOE). Optimal conditions for this electroporation were established. The introduction of a plasmid construct bearing the coding region for the large T-antigen from polyoma virus into EOE cells permitted the establishment of a derivative cell line that has the following characteristics: (1) the cells could be passaged many times; (2) they expressed a keratin-containing cytoskeleton; and (3) approx. 60% of the cells expressed amelogenin, a tissue-specific gene product unique to ameloblasts. Potential uses for such a cell line include analysis of: (1) the upstream regulatory regions required for temporally and spatially restricted expression of amelogenin; (2) the post-translational modification of amelogenin in synchronized cells and (3) the organization and biomineralization of enamel extracellular matrix in monolayer culture.