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PubMed1992

The human enamel protein gene amelogenin is expressed from both the X and the Y chromosomes.

Amelogenins, a family of extracellular matrix proteins of the dental enamel, are transiently but abundantly expressed by ameloblasts during tooth development. Amelogenins seem to regulate the formation of crystallites during the secretory stage of enamel development, while they are specifically degraded during tooth-bud maturation. In this paper we report the characterization of the AMGX and AMGY genes on the short arms of the human X and Y chromosomes which encode the amelogenins. Our studies on the expression of the amelogenin genes in male developing tooth buds showed that both the AMGX and AMGY genes are transcriptionally active and encode potentially functional proteins. We have isolated genomic and cDNA clones from both the AMGX and AMGY loci and have studied the sequence organization of these two genes. Reverse transcriptase (RT)PCR amplification of the 5' portion of the amelogenin transcripts revealed several alternatively spliced products. The splicing pattern observed in the Y-derived mRNA varies from that of the X-derived mRNA. The promoter regions from both genes and the predicted amelogenin protein sequences are presented. This information will be useful for studying the molecular basis of X-linked amelogenesis imperfecta, for understanding the evolution and regulation of gene expression on the mammalian sex chromosomes, and for investigating the role of amelogenin genes during tooth development.

Amelogenin↗
PubMed1984

Dental and maxillofacial abnormalities in long-term survivors of childhood cancer: effects of treatment with chemotherapy and radiation to the head and neck.

Sixty-eight long-term survivors of childhood cancer were evaluated for dental and maxillofacial abnormalities. Forty-five patients had received maxillofacial radiation for lymphoma, leukemia, rhabdomyosarcoma, and miscellaneous tumors. Forty-three of the 45 patients and the remaining 23 who had not received maxillofacial radiation also received chemotherapy. Dental and maxillofacial abnormalities were detected in 37 of the 45 (82%) radiated patients. Dental abnormalities comprised foreshortening and blunting of roots, incomplete calcification, premature closure of apices, delayed or arrested tooth development, and caries. Maxillofacial abnormalities comprised trismus, abnormal occlusal relationships, and facial deformities. The abnormalities were more severe in those patients who received radiation at an earlier age and at higher dosages. Possible chemotherapeutic effects in five of 23 patients who received treatment for tumors located outside the head and neck region comprised acquired amelogenesis imperfecta, microdontia of bicuspid teeth, and a tendency toward thinning of roots with an enlarged pulp chamber. Dental and maxillofacial abnormalities should be recognized as a major consequence of maxillofacial radiation in long-term survivors of childhood cancer, and attempts to minimize or eliminate such sequelae should involve an effective interaction between radiation therapists, and medical and dental oncologists.

Adolescent↗
PubMed1995

The amelogenin gene.

Amelogenin is a major protein constituent of the developing enamel matrix. This protein is now well characterized from the data of amino acid sequences which have been shown to be at a high degree of homology between all species investigated to date. The gene structure of this protein has been demonstrated and it is confirmed that there are two amelogenin genes, one on the X-chromosome and the other on the Y-chromosome in humans. The mapping of human amelogenin gene in the p22 region on the X-chromosome and the gene on the Y-chromosome was established. It has been confirmed that several types of X-linked amelogenesis imperfecta are caused by structural defects in the amelogenin gene on the X-chromosome. The physiological importance of amelogenin in the enamel formation is suggested by the symptoms of this inherited disease in addition to inhibition experiments of amelogenin transcription and translation (Couwenhoven et al., J. Craniofac. Genet. Dev. Biol. 13:259-269, 1993; Diekwisch et al., Development 117:471-482, 1993). Recently, an attempt to synthesize recombinant mouse amelogenin by E. coli was also undertaken (Simmer et al., Calcif. Tissue Int. 54:312-319, 1994). The regulation of amelogenin expression is now under investigation (Chen et al., Dev. Dynamics 199:189-198, 1994) and the elucidation of this mechanism will contribute a great deal to the study of tooth development.

Alternative Splicing↗
PubMedDate not supplied

Trichodentoosseous (TDO) syndrome: case report and literature review.

Trichodentoosseous (TDO) syndrome is an autosomal dominant condition characterized by dysplastic nails, curly hair, bone sclerosis of the long bones and calvarium, taurodontism, and enamel hypoplasia that occurs with hypomaturation/hypocalcification defects. To date, nine previous case reports of TDO in the dental literature have shown that while taurodontism and enamel defects are consistently present in TDO, the changes in the nails, hair, and bones may be variably expressed and occasionally not noted. Because of this, a few previous cases of TDO syndrome had been diagnosed simply as amelogenesis imperfecta. This case report highlights the typical clinical findings, diagnostic problems, and the clues to diagnosing this interesting condition. Clinical management of TDO is centered on preventing dental abscesses with stainless steel crowns and improving appearance with esthetic restorations.

Abnormalities, Multiple↗
PubMedDate not supplied

Microanatomy of the dental enamel in autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED): report of three cases.

Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) is an autosomal recessive disease composed of failure of various endocrine glands, chronic mucocutaneous candidiasis, and an ectodermal dystrophy complex including hypoplasia of the dental enamel. To characterize the enamel defect further, we studied enamel microanatomy by light microscopy and scanning electron microscopy in clinically affected permanent teeth from three APECED patients. In all three cases, the enamel was partially hypoplastic and morphologically aberrant. Hypoplasia was evident as a horizontal band or as rows of pits. The incremental pattern in the abnormal enamel was obscure, and the prisms were either barely detectable or accentuated and disoriented. In scanning electron microscopy, imprints of the Tomes processes were seen on the enamel surface, but the perikymata were poorly contoured. The distribution pattern of the defective enamel corresponded to the sequence of tooth development and was suggestive of a transient insult. In the enamel affected with a hypoplastic pitted from of amelogenesis imperfecta, studied for comparison, only local hypoplastic defects were seen. Together with normal parathyroid function in one patient and normal calcification of dentin in one of the two patients with hypoparathyroidism, morphology of the enamel in APECED appears to preclude calcium deficiency as the primary cause of the enamel dystrophy.

Adolescent↗
PubMed2006

Targeted expression of csCSF-1 in op/op mice ameliorates tooth defects.

OBJECTIVE: The aim of this study was to characterize the tooth phenotype of CSF-1-deficient op/op mice and determine whether expression of csCSF-1 in these mice has a role in primary tooth matrix formation. DESIGN: Ameloblasts and odontoblasts, isolated from wt/wt frozen sections using laser capture microdissection, were analysed for csCSF-1, sCSF-1 and CSF-1R mRNA by RT-PCR. Mandibles, excised from 8 days op/op and wt/wt littermates, were examined for tooth morphology as well as amelogenin and DMP1 expression using in situ hybridisation. op/opCS transgenic mice, expressing csCSF-1 in teeth and bone using the osteocalcin promoter, were generated. Skeletal X-rays and histomorphometry were performed; teeth were analysed for morphology and matrix proteins. RESULTS: Normal dental cells in vivo express both CSF-1 isoforms and CSF-1R. Compared to wt/wt, op/op teeth prior to eruption showed altered dental cell morphology and dramatic reduction in DMP1 transcripts. op/opCS mice showed marked resolution of osteopetrosis, tooth eruption and teeth that resembled amelogenesis imperfecta-like phenotype. At 3 weeks, op/op teeth showed severe enamel and dentin defects and barely detectable amelogenin and DMP1. In op/opCS mice, DMP1 in odontoblasts increased to near normal and dentin morphology was restored; amelogenin also increased. Enamel integrity improved in op/opCS, although it was thinner than wt enamel. CONCLUSIONS: Results demonstrate that ameloblasts and odontoblasts are a source and potential target of CSF-1 isoforms in vivo. Expression of csCSF-1 within the tooth microenvironment is essential for normal tooth morphogenesis and may provide a mechanism for coordinating the process of tooth eruption with endogenous matrix formation.

Ameloblasts↗
PubMed1981

The dentition in the osteogenesis imperfecta syndromes.

The deciduous and permanent teeth in some patients with osteogenesis imperfecta syndromes are blue or brown and opalescent. As shown by radiologic examination, the pulp chambers and root canals are completely or partially obliterated by abnormal dentin. The junctions between the crowns and roots are more constricted than normal. Deciduous opalescent teeth lose their enamel readily and wear more easily than normal. Unusual wear does not occur as frequently in permanent opalescent teeth as in deciduous teeth. No relationship has been shown between the number of fractures or deformity and the degree to which the teeth are affected. In contrast, other patients with osteogenesis imperfecta have normal teeth. These clinical differences in the dentitions support the concept of genetic heterogeneity is osteogenesis imperfecta and provide information useful in genetic counseling. The differential diagnosis of opalescent teeth in osteogenesis imperfecta is not difficult provided that detailed clinical and radiologic examinations of the dentition are performed. Patients with osteogenesis imperfecta and opalescent teeth should be evaluated as soon as the deciduous teeth erupt, so that an attempt can be made to prevent loss of tooth structure. However, methods of dental care in osteogenesis imperfecta are not well delineated and deserve further study.

Amelogenesis Imperfecta↗
PubMed1997

Enamel maturation.

Enamel maturation is characterized by massive crystal growth in both width and thickness, resulting in the most highly mineralized of all mammalian skeletal tissues. The control of this process is mediated via a carefully orchestrated series of events that are temporally and spatially regulated, and it requires the co-ordinated degradation and removal of the endogenous enamel matrix. This is affected by both neutral metalloproteases and serine proteases, which are developmentally restricted and may be further modulated by changes in the chemistry of the enamel crystals themselves. Failure of these mechanisms, or the adventitious entry of mineral-binding proteins during the later stages of maturation, may result in the incomplete maturation of the enamel crystals and the eruption of dysplastic tissue.

Albumins↗
PubMed1997

The protein composition of normal and developmentally defective enamel.

The development of human enamel involves a complex series of events including the secretion and degradation of a unique extracellular matrix. Ameloblasts progress through a succession of cellular phenotypes executing specialized secretory and regulatory functions. When performing optimally, ameloblasts produce a highly structured and mineralized tissue. Given the elaborate developmental events required for normal enamel formation, it is not surprising that a variety of enamel malformations arise from defects in matrix synthesis, secretion and extracellular processing. Normal matrix secretion and post-secretory processing by ameloblasts can be affected by a variety of hereditary and environmental conditions. These disturbances can result in an abnormal amount and/or composition of matrix proteins, and subsequently, an altered enamel structure and/or mineral content. For example, abnormal matrix removal during enamel maturation apparently contributes to hypomineralization associated with dental fluorosis. Incomplete matrix removal can also occur in several different forms of the hereditary condition amelogenesis imperfects. Specific types of this condition can have retention of substantial enamel protein (e.g. 5% by weight) that is, at least in part, composed of amelogenin and/or its breakdown products. Characterization of the enamel proteins in teeth affected by developmental disturbances can provide insight into the pathogenesis and normal formation of this highly specialized tissue.

Adult↗
PubMed2016

Ultrastructure of early amelogenesis in wild-type, Amelx-/-, and Enam-/- mice: enamel ribbon initiation on dentin mineral and ribbon orientation by ameloblasts.

INTRODUCTION: Dental enamel is comprised of highly organized, oriented apatite crystals, but how they form is unclear. METHODS: We used focused ion beam (FIB) scanning electron microscopy (SEM) to investigate early enamel formation in 7-week-old incisors from wild-type, Amelx-/-, and Enam-/- C56BL/6 mice. FIB surface imaging scans thicker samples so that the thin enamel ribbons do not pass as readily out of the plane of section, and generates serial images by a mill and view approach for computerized tomography. RESULTS: We demonstrate that wild-type enamel ribbons initiate on dentin mineral on the sides and tips of mineralized collagen fibers, and extend in clusters from dentin to the ameloblast membrane. The clustering suggested that groups of enamel ribbons were initiated and then extended by finger-like membrane processes as they retracted back into the ameloblast distal membrane. These findings support the conclusions that no organic nucleator is necessary for enamel ribbon initiation (although no ribbons form in the Enam-/- mice), and that enamel ribbons elongate along the ameloblast membrane and orient in the direction of its retrograde movement. Tomographic reconstruction videos revealed a complex of ameloblast membrane processes and invaginations associated with intercellular junctions proximal to the mineralization front and also highlighted interproximal extracellular enamel matrix accumulations proximal to the interrod growth sites, which we propose are important for expanding the interrod matrix and extending interrod enamel ribbons. Amelx-/- mice produce oriented enamel ribbons, but the ribbons fuse into fan-like structures. The matrix does not expand sufficiently to support formation of the Tomes process or establish rod and interrod organization. CONCLUSION: Amelogenin does not directly nucleate, shape, or orient enamel ribbons, but separates and supports the enamel ribbons, and expands the enamel matrix to accommodate continued ribbon elongation, retrograde ameloblast movement, and rod/interrod organization.

Ameloblast↗
PubMed2000

Enamel biomineralization defects result from alterations to amelogenin self-assembly.

Enamel formation is a powerful model for the study of biomineralization. A key feature common to all biomineralizing systems is their dependency upon the biosynthesis of an extracellular organic matrix that is competent to direct the formation of the subsequent mineral phase. The major organic component of forming mouse enamel is the 180-amino-acid amelogenin protein (M180), whose ability to undergo self-assembly is believed to contribute to biomineralization of vertebrate enamel. Two recently defined domains (A and B) within amelogenin appear essential for this self-assembly. The significance of these two domains has been demonstrated previously by the yeast two-hybrid system, atomic force microscopy, and dynamic light scattering. Transgenic animals were used to test the hypothesis that the self-assembly domains identified with in vitro model systems also operate in vivo. Transgenic animals bearing either a domain-A-deleted or domain-B-deleted amelogenin transgene expressed the altered amelogenin exclusively in ameloblasts. This altered amelogenin participates in the formation an organic enamel extracellular matrix and, in turn, this matrix is defective in its ability to direct enamel mineralization. At the nanoscale level, the forming matrix adjacent to the secretory face of the ameloblast shows alteration in the size of the amelogenin nanospheres for either transgenic animal line. At the mesoscale level of enamel structural hierarchy, 6-week-old enamel exhibits defects in enamel rod organization due to perturbed organization of the precursor organic matrix. These studies reflect the critical dependency of amelogenin self-assembly in forming a competent enamel organic matrix and that alterations to the matrix are reflected as defects in the structural organization of enamel.

Amelogenesis↗