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Wang X, Xing Z, Zhang X, Zhu L, Diekwisch TGH. Alternative Splicing of the Amelogenin Gene in a Caudate Amphibian, Plethodon cinereus. PLoS One 2013; 8:e68965. [PMID: 23840861 PMCID: PMC3694012 DOI: 10.1371/journal.pone.0068965] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2012] [Accepted: 06/09/2013] [Indexed: 11/25/2022] Open
Abstract
As the major enamel matrix protein contributing to tooth development, amelogenin has been demonstrated to play a crucial role in tooth enamel formation. Previous studies have revealed amelogenin alternative splicing as a mechanism for amelogenin heterogeneous expression in mammals. While amelogenin and its splicing forms in mammalian vertebrates have been characterized, splicing variants of amelogenin gene still remains largely unknown in non-mammalian species. Here, using PCR and sequence analysis we discovered two novel amelogenin transcript variants in tooth organ extracts from a caudate amphibian, the salamander Plethodoncinereus. The one was shorter -S- (416 nucleotides including untranslated regions, 5 exons) and the other larger -L- (851 nt, 7 exons) than the previously published “normal” gene in this species -M- (812 nucleotides, 6 exons). This is the first report demonstrating the amelogenin alternative splicing in amphibian, revealing a unique exon 2b and two novel amelogenin gene transcripts in Plethodoncinereus.
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Affiliation(s)
- Xinping Wang
- College of Veterinary Medicine, Jilin University, Changchun, Jilin, China
- * E-mail:
| | - Zeli Xing
- College of Veterinary Medicine, Jilin University, Changchun, Jilin, China
| | - Xichen Zhang
- College of Veterinary Medicine, Jilin University, Changchun, Jilin, China
| | - Lisai Zhu
- College of Veterinary Medicine, Jilin University, Changchun, Jilin, China
| | - Thomas G. H. Diekwisch
- College of Dentistry, University of Illinois at Chicago, Chicago, Illinois, United States of America
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Wang X, Deng X, Zhang X. Identification of a novel splicing form of amelogenin gene in a reptile, Ctenosaura similis. PLoS One 2012; 7:e45871. [PMID: 23029286 PMCID: PMC3454316 DOI: 10.1371/journal.pone.0045871] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2012] [Accepted: 08/22/2012] [Indexed: 11/18/2022] Open
Abstract
Amelogenin, the major enamel matrix protein in tooth development, has been demonstrated to play a significant role in tooth enamel formation. Previous studies have identified the alternative splicing of amelogenin in many mammalian vertebrates as one mechanism for amelogenin heterogeneous expression in teeth. While amelogenin and its splicing forms in mammalian vertebrates have been cloned and sequenced, the amelogenin gene, especially its splicing forms in non-mammalian species, remains largely unknown. To better understand the mechanism underlying amelogenin evolution, we previously cloned and characterized an amelogenin gene sequence from a squamate, the green iguana. In this study, we employed RT-PCR to amplify the amelogenin gene from the black spiny-tailed iguana Ctenosaura similis teeth, and discovered a novel splicing form of the amelogenin gene. The transcript of the newly identified iguana amelogenin gene (named C. Similis-T2L) is 873 nucleotides long encoding an expected polypeptide of 206 amino acids. The C. Similis-T2L contains a unique exon denominated exon X, which is located between exon 5 and exon 6. The C. Similis-T2L contains 7 exons including exon 1, 2, 3, 5, X, 6, and 7. Analysis of the secondary and tertiary structures of T2L amelogenin protein demonstrated that exon X has a dramatic effect on the amelogenin structures. This is the first report to provide definitive evidence for the amelogenin alternative splicing in non-mammalian vertebrates, revealing a unique exon X and the splicing form of the amelogenin gene transcript in Ctenosaura similis.
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Affiliation(s)
- Xinping Wang
- College of Veterinary Medicine, Jilin University, Changchun, Jilin, China.
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Sire JY, Huang Y, Li W, Delgado S, Goldberg M, Denbesten PK. Evolutionary story of mammalian-specific amelogenin exons 4, "4b", 8, and 9. J Dent Res 2011; 91:84-9. [PMID: 21948850 DOI: 10.1177/0022034511423399] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Amelogenin gene organization varies from 6 exons (1,2,3,5,6,7) in amphibians and sauropsids to 10 in rodents. The additional exons are exons 4, 8, 9, and "4b", the latter being as yet unidentified in AMELX transcripts. To learn more about the evolutionary origin of these exons, we used an in silico approach to find them in 39 tetrapod genomes. AMEL organization with 6 exons was the ancestral condition. Exon 4 was created in an ancestral therian (marsupials + placentals), then exon 9 in an ancestral placental, and finally exons "4b" and 8 in rodents, after divergence of the squirrel lineage. These exons were either inactivated in some lineages or remained functional: Exon 4 is functional from artiodactyls onward; exon 9 is known, to date, only in rodents, but could be coding in various mammals; and exon "4b" was probably coding in some rodents. We performed PCR of cDNA isolated from mouse and human tooth buds to identify the presence of these transcripts. A sequence analogous to exon "4b", and to exon 9, could not be amplified from the respective tooth cDNA, indicating that even though sequences similar to these exons are present, they are not transcribed in these species.
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Affiliation(s)
- J-Y Sire
- Evolution & Développement du squelette, UMR 7138, Université Pierre et Marie Curie, 7 Quai Saint-Bernard, Paris, France.
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Tsai TC, Wu SH, Chen HL, Tung YT, Cheng WTK, Huang JC, Chen CM. Identification of sex-specific polymorphic sequences in the goat amelogenin gene for embryo sexing. J Anim Sci 2011; 89:2407-14. [PMID: 21421829 DOI: 10.2527/jas.2010-3698] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Amelogenin (AMEL) is a conserved gene located on the sex chromosomes of mammals. It is involved in the formation of enamel, which is the hard, white material that forms the protective outer layer of each tooth. In this study, we first cloned and determined the intron sequences of the goat AMELX and AMELY genes from female and male ear tissues. The polymorphic AMEL alleles were further analyzed by PCR-based RFLP and Southern blot hybridization analyses. Results showed that intron 5 nucleotide sequences of the goat AMELY gene contains multiple deletions/insertions and shares only 48.5% identity to intron 5 of the goat AMELX gene. Based on the polymorphic AMEL intron sequences, a set of sex-specific triplex primers was designed to PCR amplify a single fragment of 264 bp from the X chromosome of female goats and 2 fragments of 264 and 206 bp from the X and Y chromosomes, respectively, of male goats. An increased sensitivity for sex determination was reached with a single blastomere at the blastula stage isolated from goat embryos. A total of 43 goat embryos were used to estimate a 100% accuracy rate of this method confirmed by chromosomal karyotyping and live births. The embryo sexing technique has been successfully applied in different strains of goats including Alpine, Saanen, Nubian, and Taiwan goats.
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Affiliation(s)
- T C Tsai
- Department of Life Sciences, National Chung Hsing University, Taichung 402, Taiwan
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Ding Y, Estrella MRP, Hu YY, Chan HL, Zhang HD, Kim JW, Simmer JP, Hu JCC. Fam83h is associated with intracellular vesicles and ADHCAI. J Dent Res 2009; 88:991-6. [PMID: 19828885 DOI: 10.1177/0022034509349454] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Defects in FAM83H on human chromosome 8q24.3 cause autosomal-dominant hypocalcified amelogenesis imperfecta (ADHCAI). FAM83H does not encode a recognizable signal peptide, so we predicted that the Fam83h protein functions within the cell. We tested this hypothesis by constitutively expressing mouse Fam83h with green fluorescent protein (GFP) fused to its C-terminus in HEK293 and HeLa cell lines. Green fluorescent signal from the Fam83h-GFP fusion protein was associated with perinuclear vesicles, usually in the vicinity of the Golgi apparatus. No signal was observed within the nucleus. In addition, we identified FAM83H nonsense mutations in Hispanic (C1330C>T; p.Q444X) and Caucasian (c.1192C>T; p.Q398X) families with ADHCAI. We conclude that Fam83h localizes in the intracellular environment, is associated with vesicles, and plays an important role in dental enamel formation. FAM83H is the first gene involved in the etiology of amelogenesis imperfecta (AI) that does not encode a secreted protein.
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Affiliation(s)
- Y Ding
- Department of Biologic and Materials Sciences, University of Michigan School of Dentistry, 1011 N. University, Ann Arbor, MI 48109-1078, USA
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Tanimoto K, Le T, Zhu L, Witkowska HE, Robinson S, Hall S, Hwang P, Denbesten P, Li W. Reduced amelogenin-MMP20 interactions in amelogenesis imperfecta. J Dent Res 2008; 87:451-5. [PMID: 18434575 DOI: 10.1177/154405910808700516] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Amelogenin with a proline 41 to threonine mutation (P41T) is hydrolyzed at a lower rate by matrix metalloproteinase 20 (MMP20), resulting in an inherited tooth enamel defect, amelogenesis imperfecta (AI). The aim of this study was to elucidate the effect of P41T on the interactions between amelogenin and MMP20, which may contribute to the formation of this type of AI. The interactions of a recombinant wild-type human amelogenin and its P41T mutant with recombinant human MMP20 were compared by substrate competition assay, pull-down assay, and surface plasmon resonance (SPR). The results showed that the binding of the P41T mutant amelogenin for MMP20 was significantly lower than that of wild-type amelogenin. Our study supports a model in which the P41T mutation reduces the interactions between amelogenin and MMP20, leading to decreased degradation of amelogenin by MMP20, and resulting in AI.
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Affiliation(s)
- K Tanimoto
- Department of Orofacial Sciences, School of Dentistry, University of California at San Francisco, San Francisco, CA 94143, USA
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Wiedemann-Bidlack FB, Beniash E, Yamakoshi Y, Simmer JP, Margolis HC. pH triggered self-assembly of native and recombinant amelogenins under physiological pH and temperature in vitro. J Struct Biol 2007; 160:57-69. [PMID: 17719243 PMCID: PMC2375294 DOI: 10.1016/j.jsb.2007.06.007] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2007] [Revised: 06/22/2007] [Accepted: 06/23/2007] [Indexed: 11/25/2022]
Abstract
Self-assembly of the extracellular matrix protein amelogenin is believed to play an essential role in regulating the growth and organization of enamel crystals during enamel formation. This study examines the effect of temperature and pH on amelogenin self-assembly under physiological pH conditions in vitro, using dynamic light scattering, turbidity measurements, and transmission electron microscopy. Full-length recombinant amelogenins from mouse (rM179) and pig (rP172) were investigated, along with proteolytic cleavage products (rM166 and native P148) lacking the hydrophilic C-terminus of parent molecules. Results indicated that the self-assembly of full-length amelogenin is primarily triggered by pH in the temperature range from 13 to 37 degrees C and not by temperature. Furthermore, very large assemblies of all proteins studied formed through the rearrangement of similarly sized nanospherical particles, although at different pH values: pH 7.7 (P148), pH 7.5 (rM166), pH 7.2 (rP172), and pH 7.2 (rM179). Structural differences were also observed. The full-length molecules formed apparently tightly connected elongated, high-aspect ratio assemblies comprised of small spheres, while the amelogenin cleavage products appeared as loosely associated spherical particles, suggesting that the hydrophilic C-terminus plays an essential role in higher-order amelogenin assembly. Hence, tightly controlled pH values during secretory amelogenesis may serve to regulate the functions of both full-length and cleaved amelogenins.
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Iwase M, Kaneko S, Kim H, Satta Y, Takahata N. Evolutionary History of Sex-Linked Mammalian Amelogenin Genes. Cells Tissues Organs 2007; 186:49-59. [PMID: 17627118 DOI: 10.1159/000102680] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Amelogenin (AMEL) arose prior to the emergence of tetrapods and transposed into an intron of the Rho GTPase-activating protein 6 gene. In the mammalian lineage leading to eutherians, a pair of homologous autosomes with this nested gene structure fused with the then already differentiating sex chromosomes by suppressing homologous recombination. As sex-chromosomal differentiation extended to the fused region, a pair of homologous AMEL genes too differentiated from each other in two steps; first in the 5' region (the promoter region to transposon MER5 in intron 2) and second in the remaining 3' region. This resulted in gametologous AMELX and AMELY in the eutherian sex chromosomes. Although the early differentiation of the 5' region between AMELX and AMELY is consistent with the lowered expression level of AMELY, there is no indication for deterioration of AMELY at the amino acid level. Rather, both AMELX and AMELY in particular lineages might undergo positive selection, followed by negative selection to preserve established function. Based on patterns and levels of AMELX and AMELY polymorphisms in the human population, it is also argued that a recombination cold spot near AMELX might be related to the cause of the ancient pseudoautosomal boundary.
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Affiliation(s)
- Mineyo Iwase
- Department of Biosystems Science, Graduate University for Advanced Studies, Hayama, Japan
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9
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Wang X, Fan JL, Ito Y, Luan X, Diekwisch TGH. Identification and characterization of a squamate reptilian amelogenin gene: Iguana iguana. JOURNAL OF EXPERIMENTAL ZOOLOGY PART B-MOLECULAR AND DEVELOPMENTAL EVOLUTION 2006; 306:393-406. [PMID: 16506230 DOI: 10.1002/jez.b.21096] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
As the principal components of the developing tooth enamel matrix, amelogenins play a significant role in tooth enamel formation and organization. In order to elucidate the structure and function of amelogenins in the evolution of enamel, we have selected the Iguana iguana as a squamate model organism. Here we report the first complete squamate amelogenin sequence available as of yet and document unique features of Iguana amelogenins and enamel. Transmission electron microscopy documented randomly oriented Iguana enamel crystals during the elongation phase compared with organized enamel crystal patterns at comparable stages in mammals. Sequencing of PCR amplified products revealed a full-length I. iguana amelogenin cDNA containing 877 nucleotides with a 564 nucleotide coding sequence encoding 187 amino acids. The homologies of the newly discovered I. iguana amelogenin amino acid sequence with the published mouse, caiman (Palaeosuchus), and snake (Elaphe) amelogenin were 41.3%, 53.5%, and 55.5%, respectively. On Western blots one major protein with a molecular weight of 24 kDa, and two minor proteins with molecular weights of 28 and 13.5 kDa, respectively, were detected based on the cross-reactivity of antisera against recombinant Rana pipiens amelogenin proteins. Sequence analysis revealed a moderate sequence homology between mammalian and reptilian amelogenin genes. A significant alteration was the deletion of the hydrophilic GSP sequence from exon 3 in the mouse sequence resulting in a conversion to a hydrophobic region in Iguana. Together, these findings identified a novel amelogenin cDNA sequence in the squamate reptilian I. iguana and functional implications for the evolution of amelogenins and enamel in squamates.
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Affiliation(s)
- Xinping Wang
- Department of Oral Biology and Allan G. Brodie Laboratory for Craniofacial Genetics, College of Dentistry, University of Illinois at Chicago, Chicago, Illinois 60612, USA
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10
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Diekwisch TGH, Wang X, Fan JL, Ito Y, Luan X. Expression and characterization of a Rana pipiens amelogenin protein. Eur J Oral Sci 2006; 114 Suppl 1:86-92; discussion 93-5, 379-80. [PMID: 16674667 DOI: 10.1111/j.1600-0722.2006.00302.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Amelogenin, the major protein of developing enamel matrix, controls enamel crystal growth via unique supermolecular features. While much has been contributed to our understanding of mammalian amelogenin function, little is known about how amelogenin and its unique physico-chemical features have evolved among vertebrates. Here we report, for the first time, amphibian amelogenin recombinant protein expression and characterization in Rana pipiens. In order to characterize R. pipiens amelogenin, the newly discovered amelogenin coding sequence was amplified, subcloned, and expressed in Eshcerichia coli. Our newly generated R. pipiens amelogenin-specific antisera resolved a major 19-kDa band on western blots of frog tooth extracts and revealed an enamel organ tissue-specific localization pattern using immunohistochemistry. Using mass spectroscopy, a single major compound with a molecular weight of 21.6 kDa was detected, which corresponded to the amino acid sequence-based molecular weight prediction of the His fusion recombinant protein. Dynamic light scattering studies resolved 41-nm radius subunits compared with 14-nm radius subunits from mouse recombinant amelogenin controls. Transmission electron microscopy revealed defined spherical subunits in R. pipiens matrix self-assembly in contrast with a homogeneous 'stippled' matrix in mouse amelogenin matrix self-assembly. Our data suggest that R. pipiens amelogenin is distinguished from mammalian amelogenins by a number of unique physico-chemical properties which may be related to specific modes of crystal formation in frog enamel.
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Affiliation(s)
- T G H Diekwisch
- Department of Oral Biology and Allan G. Brodie Laboratory for Craniofacial Genetics, College of Dentistry, University of Illinois at Chicago, Chicago, IL 60612, USA.
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Samollow PB. Status and applications of genomic resources for the gray, short-tailed opossum, Monodelphis domestica, an American marsupial model for comparative biology. AUST J ZOOL 2006. [DOI: 10.1071/zo05059] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Owing to its small size, favourable reproductive characteristics, and simple husbandry, the gray, short-tailed opossum, Monodelphis domestica, has become the most widely distributed and intensively utilised laboratory-bred research marsupial in the world today. This article provides an overview of the current state and future projections of genomic resources for this species and discusses the potential impact of this growing resource base on active research areas that use M. domestica as a model system. The resources discussed include: fully arrayed, bacterial artificial chromosome (BAC) libraries; an expanding linkage map; developing full-genome BAC-contig and chromosomal fluorescence in situ hybridisation maps; public websites providing access to the M. domestica whole-genome-shotgun sequence trace database and the whole-genome sequence assembly; and a new project underway to create an expressed-sequence database and microchip expression arrays for functional genomics applications. Major research areas discussed span a variety of genetic, evolutionary, physiologic, reproductive, developmental, and behavioural topics, including: comparative immunogenetics; genomic imprinting; reproductive biology; neurobiology; photobiology and carcinogenesis; genetics of lipoprotein metabolism; developmental and behavioural endocrinology; sexual differentiation and development; embryonic and fetal development; meiotic recombination; genome evolution; molecular evolution and phylogenetics; and more.
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12
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Delgado S, Girondot M, Sire JY. Molecular evolution of amelogenin in mammals. J Mol Evol 2005; 60:12-30. [PMID: 15696365 DOI: 10.1007/s00239-003-0070-8] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2003] [Accepted: 07/21/2004] [Indexed: 10/25/2022]
Abstract
An evolutionary analysis of mammalian amelogenin, the major protein of forming enamel, was conducted by comparison of 26 sequences (including 14 new ones) representative of the main mammalian lineages. Amelogenin shows highly conserved residues in the hydrophilic N- and C-terminal regions. The central hydrophobic region (most of exon 6) is more variable, but it has conserved a high amount of proline and glutamine located in triplets, PXQ, indicating that these residues play an important role. This region evolves more rapidly, and is less constrained, than the other well-conserved regions, which are subjected to strong constraints. The comparison of the substitution rates in relation to the CpG richness confirmed that the highly conserved regions are subjected to strong selective pressures. The amino acids located at important sites and the residues known to lead to amelogenesis imperfecta when substituted were present in all sequences examined. Evolutionary analysis of the variable region of exon 6 points to a particular zone, rich in either amino acid insertion or deletion. We consider this region a hot spot of mutation for the mammalian amelogenin. In this region, numerous triplet repeats (PXQ) have been inserted recently and independently in five lineages, while most of the hydrophobic exon 6 region probably had its origin in several rounds of triplet insertions, early in vertebrate evolution. The putative ancestral DNA sequence of the mammalian amelogenin was calculated using a maximum likelihood approach. The putative ancestral protein was composed of 177 residues. It already contained all important amino acid positions known to date, its hydrophobic variable region was rich in proline and glutamine, and it contained triplet repeats PXQ as in the modern sequences.
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Affiliation(s)
- Sidney Delgado
- FRE2696, Equipe Evolution & Développement du Squelette, Université Paris 6, Paris, France
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Wang X, Ito Y, Luan X, Yamane A, Diekwisch TGH. Amelogenin sequence and enamel biomineralization in Rana pipiens. JOURNAL OF EXPERIMENTAL ZOOLOGY PART B-MOLECULAR AND DEVELOPMENTAL EVOLUTION 2005; 304:177-86. [PMID: 15744754 DOI: 10.1002/jez.b.21035] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The amelogenin gene contributes the majority of tooth enamel proteins and plays a significant role in enamel biomineralization. While several mammalian and reptilian amelogenins have been cloned and sequenced, basal vertebrate amelogenin evolution remains to be understood. In order to start elucidating the structure and function of amelogenins in the evolution of enamel, the leopard frog (Rana pipiens) was used as a model. Tissues from Rana pipiens teeth were analyzed for enamel structure and RNA extracts were processed for sequence analysis. Electron microscopy revealed that Rana pipiens enamel contains long and parallel crystals similar to mammalian enamel, while immunoreactions confirmed the site-specific localization of cross-reactive amelogenins in Rana pipiens enamel. Sequencing of amelogenin PCR products revealed a 782bp cDNA with a 546-nucleotide coding sequence encoding 181 amino acids. The homology of the newly discovered Rana pipiens amelogenin nucleotide and amino acid sequence with the published mouse amelogenin was 38.6% and 45%, respectively. These findings report the first complete amelogenin cDNA sequence in amphibians and indicate a close homology between mammalian enamel formation and Rana pipiens enamel biomineralization.
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Affiliation(s)
- Xinping Wang
- Department of Oral Biology and Allan G. Brodie Laboratory for Craniofacial Genetics, College of Dentistry, University of Illinois at Chicago, Chicago, Illinois 60612, USA
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14
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Samollow PB, Kammerer CM, Mahaney SM, Schneider JL, Westenberger SJ, VandeBerg JL, Robinson ES. First-generation linkage map of the gray, short-tailed opossum, Monodelphis domestica, reveals genome-wide reduction in female recombination rates. Genetics 2004; 166:307-29. [PMID: 15020427 PMCID: PMC1470690 DOI: 10.1534/genetics.166.1.307] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The gray, short-tailed opossum, Monodelphis domestica, is the most extensively used, laboratory-bred marsupial resource for basic biologic and biomedical research worldwide. To enhance the research utility of this species, we are building a linkage map, using both anonymous markers and functional gene loci, that will enable the localization of quantitative trait loci (QTL) and provide comparative information regarding the evolution of mammalian and other vertebrate genomes. The current map is composed of 83 loci distributed among eight autosomal linkage groups and the X chromosome. The autosomal linkage groups appear to encompass a very large portion of the genome, yet span a sex-average distance of only 633.0 cM, making this the most compact linkage map known among vertebrates. Most surprising, the male map is much larger than the female map (884.6 cM vs. 443.1 cM), a pattern contrary to that in eutherian mammals and other vertebrates. The finding of genome-wide reduction in female recombination in M. domestica, coupled with recombination data from two other, distantly related marsupial species, suggests that reduced female recombination might be a widespread metatherian attribute. We discuss possible explanations for reduced female recombination in marsupials as a consequence of the metatherian characteristic of determinate paternal X chromosome inactivation.
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Affiliation(s)
- Paul B Samollow
- Department of Genetics, Southwest Foundation for Biomedical Research, San Antonio, Texas, 78245-0549, USA.
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15
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Abstract
Dental enamel forms as a progressively thickening extracellular layer by the action of proteins secreted by ameloblasts. The most abundant enamel protein is amelogenin, which is expressed primarily from a gene on the X-chromosome (AMELX). The two most abundant non-amelogenin enamel proteins are ameloblastin and enamelin, which are expressed from the AMBN and ENAM genes, respectively. The human AMBN and ENAM genes are located on chromosome 4q13.2. The major secretory products of the human AMELX, AMBN, and ENAM genes have 175, 421, and 1103 amino acids, respectively, and are all post-translationally modified, secreted, and processed by proteases. Mutations in AMELX have been shown to cause X-linked amelogenesis imperfecta (AI), which accounts for 5% of AI cases. Mutations in ENAM cause a severe form of autosomal-dominant smooth hypoplastic AI that represents 1.5%, and a mild form of autosomal-dominant local hypoplastic AI that accounts for 27% of AI cases in Sweden. The discovery of mutations in the ENAM gene in AI kindreds proved that enamelin is critical for proper dental enamel formation and that it plays a role in human disease. Here we review how enamelin was discovered, what is known about enamelin protein structure, post-translational modifications, processing by proteases, and its potentially important functional properties such as its affinity for hydroxyapatite and influence on crystal growth in vitro. The primary structures of human, porcine, mouse, and rat enamelin are compared, and the human enamelin gene, its structure, chromosomal localization, temporal and spatial patterns of expression, and its role in the etiology of amelogenesis imperfecta are discussed.
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Affiliation(s)
- J C-C Hu
- Department of Orthodontics and Pediatric Dentistry, University of Michigan, School of Dentistry, 1011 North University, Ann Arbor, MI 48109-1078, USA.
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16
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Chen E, Yuan ZA, Wright JT, Hong SP, Li Y, Collier PM, Hall B, D'Angelo M, Decker S, Piddington R, Abrams WR, Kulkarni AB, Gibson CW. The small bovine amelogenin LRAP fails to rescue the amelogenin null phenotype. Calcif Tissue Int 2003; 73:487-95. [PMID: 12958690 DOI: 10.1007/s00223-002-0036-7] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/15/2002] [Accepted: 03/17/2003] [Indexed: 11/25/2022]
Abstract
Amelogenins are the most abundant secreted proteins in developing dental enamel. These evolutionarily-conserved proteins have important roles in enamel mineral formation, as mutations within the amelogenin gene coding region lead to defects in enamel thickness or mineral structure. Because of extensive alternative splicing of the primary RNA transcript and proteolytic processing of the secreted proteins, it has been difficult to assign functions to individual amelogenins. To address the function of one of the amelogenins, we have created a transgenic mouse that expresses bovine leucine-rich amelogenin peptide (LRAP) in the enamel-secreting ameloblast cells of the dental organ. Our strategy was to breed this transgenic mouse with the recently generated amelogenin knockout mouse, which makes none of the amelogenin proteins and has a severe hypoplastic and disorganized enamel phenotype. It was found that LRAP does not rescue the enamel defect in amelogenin null mice, and enamel remains hypoplastic and disorganized in the presence of this small amelogenin. In addition, LRAP overexpression in the transgenic mouse (wildtype background) leads to pitting in the enamel surface, which may result from excess protein production or altered protein processing due to minor differences between the amino acid compositions of murine and bovine LRAP. Since introduction of bovine LRAP into the amelogenin null mouse does not restore normal enamel structure, it is concluded that other amelogenin proteins are essential for normal appearance and function.
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Affiliation(s)
- E Chen
- Department of Anatomy and Cell Biology, University of Pennsylvania School of Dental Medicine, 240 S. 40th St., Philadelphia, PA, USA
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17
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Abstract
Proteinases serve two important functions during dental enamel formation: They (a) process and (b) degrade enamel proteins. Different enzymes carry out these functions. Enamelysin (MMP-20) is the foremost enamel matrix-processing enzyme. Its expression initiates prior to the onset of dentin mineralization and continues throughout the secretory stage of amelogenesis. In vitro, enamelysin catalyzes all of the amelogenin cleavages that are known to occur during the secretory stage in vivo, and it is probably the enzyme responsible for the processing of all enamel proteins. There is evidence suggesting that enamelysin activity is critical for proper enamel formation. Uncleaved and processed enamel proteins often segregate into different compartments within the developing enamel layer, suggesting that they may have different functions. Intact ameloblastin and its C-terminal cleavage products localize in the superficial rod and interrod enamel, while its N-terminal cleavage products congregate in the sheath space. Intact enamelin is only present at the mineralization front within a micrometer of the enamel surface, while its cleavage products concentrate in the rod and interrod enamel. Processed enamel proteins accumulate during the secretory stage, but disappear early in the maturation stage. Enamel matrix serine proteinase 1 (EMSP1), now officially designated kallikrein 4 (KLK4), is believed to be the predominant degradative enzyme that clears enamel proteins from the matrix during maturation. KLK4 expression initiates during the transition stage and continues throughout maturation. KLK4 concentrates at the enamel surface when the enamel matrix disappears, and aggressively degrades amelogenin in vitro. During tooth development, proteinases are secreted by ameloblasts into the extracellular space, where they cleave enamel proteins by catalyzing the hydrolysis of peptide bonds. Enamel proteinases are present in low abundance and are not likely to participate directly in the mineralization process. Two major enamel proteinases have been identified: enamelysin (MMP20) and kallikrein 4 (KLK4). These proteinases are expressed at different times and have different functions. Their roles are to modify and/or to eliminate enamel matrix proteins, which affects the way enamel proteins interact with each other and with the developing enamel crystallites. A brief review of dental enamel formation is presented, followed by a more detailed analysis of enamelysin and KLK4 expression, structure, and function.
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Affiliation(s)
- James P Simmer
- University of Texas Health Science Center at San Antonio, Department of Pediatric Dentistry, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900, USA.
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18
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Hu CC, Ryu OH, Yamakoshi Y, Zhang CH, Cao X, Qian Q, Simmer JP. Pig amelogenin gene expresses a unique exon 4. Connect Tissue Res 2003; 43:435-40. [PMID: 12489195 DOI: 10.1080/03008200290001140] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The pig amelogenin gene was isolated from a Lambda genomic library, and a 6.3 kb SalI/XbaI restriction fragment, inclusive of exons 3 through 7, was subcloned into a plasmid vector. DNA sequencing revealed two putative exon 4 sequences. The derived amino acid sequence of exon 4a, KSGRWGARLTAFVSSVQ, had previously been identified in a 190-amino-acid amelogenin isoform by protein sequencing. Exon 4b encoded the peptide DLYLEAIRIDRTAF, which is homologous to exon 4-encoded segments reported for human, mouse, and rat. Oligonucleotides from both of these exons were used to amplify cDNA generated from developing teeth. Amplification products were analyzed by agarose gel electrophoresis, cloned, and characterized by DNA sequencing. Exon 4a was found in transcripts encoding amelogenin isoforms having 190 and 73 amino acids. Exon 4b was found only in apparent splicing intermediates that retained intron 3, but was not detected in any final mRNA transcripts. Pig amelogenin having apparent molecular mass of 23 kD were isolated from the enamel matrix and characterized by mass spectrometry. Two mass values, 18,512.5, and 18,571.2 Da, were measured that match the values predicted for the 162-amino-acid cleavage product of the 173-amino-acid amelogenin, and the 165-amino-acid cleavage product of the 190-amino-acid amelogenin, which includes 17 amino acids encoded by exon 4a. We conclude that the pig amelogenin gene expresses a unique exon 4 that is not homologous to, or evolved from, the exon 4 segment expressed in humans and rodents.
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Affiliation(s)
- C C Hu
- University of Texas School of Dentistry, Health Science Center at San Antonio, Department of Pediatric Dentistry, 7703 Floyd Curl Drive, San Antonio, TX 78284-7888, USA.
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19
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Hu CC, Simmer JP, Bartlett JD, Qian Q, Zhang C, Ryu OH, Xue J, Fukae M, Uchida T, MacDougall M. Murine enamelin: cDNA and derived protein sequences. Connect Tissue Res 2001; 39:47-61; discussion 63-7. [PMID: 11062988 DOI: 10.3109/03008209809023911] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Enamelin is the largest enamel protein. Recently we reported the characterization of a cDNA clone encoding porcine enamelin. The secreted protein has 1104 amino acids--over 6 times the length of amelogenin (173 amino acids) and almost 3 times the lengths of sheathlin (395 amino acids) and tuftelin (389 amino acids). Immunohistochemistry has shown that uncleaved porcine enamelin concentrates at the growing tips of the enamel crystallites while its cleavage products localize to rod and interrod enamel. Here we report the isolation and characterization of cDNA encoding murine amelogenin and demonstrate the tooth specificity of porcine enamelin. The murine clone is 4154 nucleotides in length and encodes a protein of 1274 amino acids. In the absence of post-translational modifications murine enamelin has an isotope averaged molecular mass of 137 kDa and an isoelectric point of 9.4. Multiple tissue Northern blot analyses detect porcine enamelin mRNA in developing teeth but not in liver, heart, brain, spleen, skeletal muscle and lung. Mouse and porcine enamelin share 61% amino acid identity and 75% DNA sequence identity. Mouse enamelin has 14 tandemly arranged copies of an 11 amino acid segment that is found only once in porcine enamelin.
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Affiliation(s)
- C C Hu
- University of Texas Health Science Center at San Antonio, School of Dentistry, Department of Pediatric Dentistry, 78284-7888, USA.
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20
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Moradian-Oldak J, Paine ML, Lei YP, Fincham AG, Snead ML. Self-assembly properties of recombinant engineered amelogenin proteins analyzed by dynamic light scattering and atomic force microscopy. J Struct Biol 2000; 131:27-37. [PMID: 10945967 DOI: 10.1006/jsbi.2000.4237] [Citation(s) in RCA: 138] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Dynamic light scattering (DLS) analysis together with atomic force microscopy (AFM) imaging was applied to investigate the supramolecular self-assembly properties of a series of recombinant amelogenins. The overall objective was to ascertain the contribution of certain structural motifs in amelogenin to protein-protein interactions during the self-assembly process. Mouse amelogenins lacking either amino- or carboxy-terminal domains believed to be involved in self-assembly and amelogenins having single or double amino acid mutations identical to those found in cases of amelogenesis imperfecta were analyzed. The polyhistidine-containingfull-length recombinant amelogenin protein [rp(H)M180] generated nanospheres with monodisperse size distribution (hydrodynamic radius of 20.7 +/- 2.9 nm estimated from DLS and 16.1 +/- 3.4 nm estimated from AFM images), comparable to nanospheres formed by full-length amelogenin rM179 without the polyhistidine domain, indicating that this histidine modification did not interfere with the self-assembly process. Deletion of the N-terminal self-assembly domain from amelogenin and their substitution by a FLAG epitope ("A"-domain deletion) resulted in the formation of assemblies with a heterogeneous size distribution with the hydrodynamic radii of particles ranging from 3 to 38 nm. A time-dependent dynamic light scattering analysis of amelogenin molecules lacking amino acids 157 through 173 and containing a hemagglutinin epitope ("B"-domain deletion) resulted in the formation of particles (21.5 +/- 6.8 nm) that fused to form larger particles of 49.3 +/- 4.3 nm within an hour. Single and double point mutations in the N-terminal region resulted in the formation of larger and more heterogeneous nanospheres. The above data suggest that while the N-terminal A-domain is involved in the molecular interactions for the formation of nanospheres, the carboxy-terminal B-domain contributes to the stability and homogeneity of the nanospheres, preventing their fusion to larger assemblies. These in vitro findings support the notion that the proteolytic cleavage of amelogenin at amino- and carboxy-terminii occurring during enamel formation influences amelogenin to amelogenin interactions during self-assembly and hence alters the structural organization of the developing enamel extracellular matrix, thus affecting enamel biomineralization.
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Affiliation(s)
- J Moradian-Oldak
- Center for Craniofacial Molecular Biology, School of Dentistry, University of Southern California, California, Los Angeles 90033, USA
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21
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Chen WY, Bell AW, Simmer JP, Smith CE. Mass spectrometry of native rat amelogenins: primary transcripts, secretory isoforms, and C-terminal degradation. J Dent Res 2000; 79:840-9. [PMID: 10765958 DOI: 10.1177/00220345000790031001] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Cloning technologies have established unambiguously that amelogenins always seem larger in molecular weight (Mr) by gel electrophoresis (SDS-PAGE) than by mass spectrometry (MS). This has caused many problems relating cloned versions of amelogenin to proteins actually secreted by ameloblasts in vivo. In this study, discrete protein fractions at 31-20 kDa (Mr(SDS)) were prepared from freeze-dried rat incisor enamel by techniques optimized for preserving protein integrity. N-terminal sequence and amino acid compositional analyses indicated that the major protein forming these fractions was amelogenin. As expected, the molecular weights estimated by matrix-assisted laser desorption ionization (MALDI) and electrospray ionization (ESI) MS were significantly less than their apparent molecular weights estimated by SDS-PAGE. Plots of Mr(SDS) vs. Mr(MS) for all fractions showed high linear correlation (r = 0.992). Analysis of MS data further indicated that the major protein in the 27-kDa fraction corresponded to the R180 secretory isoform of rat amelogenin, whereas some minor proteins in the 23-kDa fraction likely corresponded to a R156 secretory isoform. This was in contrast to major proteins forming the 25-, 24-, and 23-kDa fractions (Mr(SDS)), which seemed to represent proteolytic fragments of R180 progressively altered at the P169-A170, P164-L165, and F151-S152 C-terminal cleavage sites, respectively. Proteins in the 20-kDa fraction (Mr(SDS)) most closely matched by ESI-MS fragments of the R156 secretory isoform that were C-terminally-modified at the equivalent P164-L165 site.
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Affiliation(s)
- W Y Chen
- Division of Oral Biology, Faculty of Dentistry, McGill University, Montreal, QC, Canada
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22
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Chen CM, Hu CL, Wang CH, Hung CM, Wu HK, Choo KB, Cheng WT. Gender determination in single bovine blastomeres by polymerase chain reaction amplification of sex-specific polymorphic fragments in the amelogenin gene. Mol Reprod Dev 1999; 54:209-14. [PMID: 10497342 DOI: 10.1002/(sici)1098-2795(199911)54:3<209::aid-mrd1>3.0.co;2-6] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
A sensitive technique for the sexing of bovine embryos was developed using polymerase chain reaction (PCR) amplification of the bovine amelogenin (bAML) gene on the X- and Y-chromosomes of Holstein dairy cattle. Cloning and DNA sequencing showed a 45.1% homology between the fifth intron of the bAML-X and bAML-Y gene with multiple deletions. A pair of sex-specific primers was designed to allow amplification of a single fragment of 467-bp from the X-chromosome of female cattle and two fragments of 467-bp and 341-bp from the X- and Y-chromosomes of male cattle. The primers were successfully applied to bovine sexing from single blastomeres isolated from day-6 to day-7 cow embryos by direct cell lysis and PCR. Our protocol of embryo sexing should be applicable to the diagnosis of defective genes in vitro in human embryos and in other domestic or recreational animals.
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Affiliation(s)
- C M Chen
- Department of Zoology, College of Life Science, National Chung Hsing University, Taichung, Taiwan, Republic of China
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23
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Kogaya Y. Immunohistochemical localisation of amelogenin-like proteins and type I collagen and histochemical demonstration of sulphated glycoconjugates in developing enameloid and enamel matrices of the larval urodele (Triturus pyrrhogaster) teeth. J Anat 1999; 195 ( Pt 3):455-64. [PMID: 10580861 PMCID: PMC1468015 DOI: 10.1046/j.1469-7580.1999.19530455.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The presence of collagen in enameloid distinguishes it clearly from true enamel, but little is known about the phylogenetic relationship between these 2 tissues. It has previously been reported that amelogenins are the principal proteins of the enamel matrix, that type I collagen and chondroitin sulphates are the predominant matrices in dentine, and that amphibian and reptilian aprismatic enamels, contain no sulphated glycoconjugates, although certain sulphated substances are secreted into mammalian prismatic enamel during matrix formation. The larval urodele (Triturus pyrrhogaster) teeth are known to be composed of enameloid, dentine, and enamel-like tissue. To characterise the tooth matrices, the localisation of amelogenin-like proteins, type I collagen, and sulphated glycoconjugates was investigated. Chondroitin sulphates and fine fibrils immunoreactive for type I collagen were elaborated as the enameloid matrix inside the dental basement membrane. After the matrix had been deposited in full thickness, coarse collagen fibrils also immunoreactive for type I collagen and chondroitin sulphates were deposited below as the first dentine matrix. Further, enamel-like matrix with no collagen fibrils or sulphated glycoconjugates but strongly immunoreactive for amelogenins was deposited on the dentine. Although no immunolabelling for amelogenins was found over the enameloid matrix, at least at the formation stage, the zone of coarse collagen fibrils of dentine was partially immunoreactive as observed in mammalian mantle dentine. From the ontogeny and matrix constituents of larval urodele teeth, it is suggested that enameloid is originally a dentine-like tissue.
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Affiliation(s)
- Y Kogaya
- Department of Oral Anatomy, Asahi University School of Dentistry, Gifu, Japan.
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24
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Fincham AG, Moradian-Oldak J, Simmer JP. The structural biology of the developing dental enamel matrix. J Struct Biol 1999; 126:270-99. [PMID: 10441532 DOI: 10.1006/jsbi.1999.4130] [Citation(s) in RCA: 474] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The biomineralization of the dental enamel matrix with a carbonated hydroxyapatite mineral generates one of the most remarkable examples of a vertebrate mineralized tissue. Recent advances in the molecular biology of ameloblast gene products have now revealed the primary structures of the principal proteins involved in this extracellular mineralizing system, amelogenins, tuftelins, ameloblastins, enamelins, and proteinases, but details of their secondary, tertiary, and quaternary structures, their interactions with other matrix and or cell surface proteins, and their functional role in dental enamel matrix mineralization are still largely unknown. This paper reviews our current knowledge of these molecules, the probable molecular structure of the enamel matrix, and the functional role of these extracellular matrix proteins. Recent studies on the major structural role played by the amelogenin proteins are discussed, and some new data on synthetic amelogenin matrices are reviewed.
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Affiliation(s)
- A G Fincham
- Center for Craniofacial Molecular Biology, School of Dentistry, Los Angeles, California 90089, USA
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25
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Toyosawa S, O'hUigin C, Figueroa F, Tichy H, Klein J. Identification and characterization of amelogenin genes in monotremes, reptiles, and amphibians. Proc Natl Acad Sci U S A 1998; 95:13056-61. [PMID: 9789040 PMCID: PMC23708 DOI: 10.1073/pnas.95.22.13056] [Citation(s) in RCA: 113] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Two features make the tooth an excellent model in the study of evolutionary innovations: the relative simplicity of its structure and the fact that the major tooth-forming genes have been identified in eutherian mammals. To understand the nature of the innovation at the molecular level, it is necessary to identify the homologs of tooth-forming genes in other vertebrates. As a first step toward this goal, homologs of the eutherian amelogenin gene have been cloned and characterized in selected species of monotremes (platypus and echidna), reptiles (caiman), and amphibians (African clawed toad). Comparisons of the homologs reveal that the amelogenin gene evolves quickly in the repeat region, in which numerous insertions and deletions have obliterated any similarity among the genes, and slowly in other regions. The gene organization, the distribution of hydrophobic and hydrophilic segments in the encoded protein, and several other features have been conserved throughout the evolution of the tetrapod amelogenin gene. Clones corresponding to one locus only were found in caiman, whereas the clawed toad possesses at least two amelogenin-encoding loci.
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Affiliation(s)
- S Toyosawa
- Max-Planck-Institut für Biologie, Abteilung Immungenetik, Corrensstrasse 42, D-72076 Tübingen, Germany
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26
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Smith CE. Cellular and chemical events during enamel maturation. CRITICAL REVIEWS IN ORAL BIOLOGY AND MEDICINE : AN OFFICIAL PUBLICATION OF THE AMERICAN ASSOCIATION OF ORAL BIOLOGISTS 1998; 9:128-61. [PMID: 9603233 DOI: 10.1177/10454411980090020101] [Citation(s) in RCA: 497] [Impact Index Per Article: 19.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
This review focuses on the process of enamel maturation, a series of events associated with slow, progressive growth in the width and thickness of apatitic crystals. This developmental step causes gradual physical hardening and transformation of soft, newly formed enamel into one of the most durable mineralized tissues produced biologically. Enamel is the secretory product of specialized epithelial cells, the ameloblasts, which make this covering on the crowns of teeth in two steps. First, they roughly "map out" the location and limits (overall thickness) of the entire extracellular layer as a protein-rich, acellular, and avascular matrix filled with thin, ribbon-like crystals of carbonated hydroxyapatite. These initial crystals are organized spatially into rod and interrod territories as they form, and rod crystals are lengthened by Tomes' processes in tandem with appositional movement of ameloblasts away from the dentin surface. Once the full thickness of enamel has been formed, ameloblasts initiate a series of repetitive morphological changes at the enamel surface in which tight junctions and deep membrane infoldings periodically appear (ruffle-ended), then disappear for short intervals (smooth-ended), from the apical ends of the cells. As this happens, the enamel covered by these cells changes rhythmically in net pH from mildly acidic (ruffle-ended) to near-physiologic (smooth-ended) as mineral crystals slowly expand into the "spaces" (volume) formerly occupied by matrix proteins and water. Matrix proteins are processed and degraded by proteinases throughout amelogenesis, but they undergo more rapid destruction once ameloblast modulation begins. Ruffle-ended ameloblasts appear to function primarily as a regulatory and transport epithelium for controlling the movement of calcium and other ions such as bicarbonate into enamel to maintain buffering capacity and driving forces optimized for surface crystal growth. The reason ruffle-ended ameloblasts become smooth-ended periodically is unknown, although this event seems to be crucial for sustaining long-term crystal growth.
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Affiliation(s)
- C E Smith
- Faculty of Dentistry, and Department of Anatomy & Cell Biology, McGill University, Montreal, Quebec, Canada
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27
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Hu CC, Ryu OH, Qian Q, Zhang CH, Simmer JP. Cloning, characterization, and heterologous expression of exon-4-containing amelogenin mRNAs. J Dent Res 1997; 76:641-7. [PMID: 9062557 DOI: 10.1177/00220345970760020401] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The formation of dental enamel is dependent upon amelogenins, a family of proteins constituting most of the developing enamel matrix. Depending upon the species, these enamel proteins are expressed from either one or two copies of the amelogenin gene. Each gene directs the synthesis of a variety of amelogenin isoforms through alternative splicing of their pre-mRNA transcript(s). Before the role of amelogenins in dental enamel formation can be better understood, one must know the isoforms that are secreted and their biochemical properties. Previously, we cloned and characterized 7 mouse amelogenin RNA messages generated by alternative splicing. The largest amelogenin cDNA encoded a 194-residue amelogenin isoform which was the only clone to contain the 42-nucleotide exon 4 segment. Anti-peptide antibodies raised against the derived translation of this exon revealed an unexpectedly diverse assortment of murine amelogenins, suggesting that additional splicing variants could contain the exon 4 coding region. Using exon-4-specific oligonucleotide primers, we have amplified, cloned, and characterized three different amelogenin RNA messages. These messages encode amelogenin polypeptides (exclusive of signal peptides) 194, 170, and 73 amino acids in length. The isotope-averaged molecular weights for the deduced, single-phosphorylated, proteins are 21,897.1, 19,113.9, and 8176.5 Daltons, respectively. Splice-site selection for the generation of these mRNAs was identical to that of the previously characterized messages for the M180, M156, and M59 except for the inclusion of exon 4. The exon-4-containing amelogenin isoforms were heterologously expressed in E. coli by means of the pET11 expression system (Novagen, Madison, WI).
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Affiliation(s)
- C C Hu
- University of Texas School of Dentistry, Health Science Center at San Antonio, Department of Pediatric Dentistry 78284-7888, USA
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