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A curriculum vitae of teeth: evolution, generation, regeneration.

Koussoulakou DS, Margaritis LH, Koussoulakos SL - Int. J. Biol. Sci. (2009)

Bottom Line: Over the course of 500,000,000 years of evolution, many of those structures migrated into the mouth cavity.In addition, the total number of teeth per dentition generally decreased and teeth morphological complexity increased.These interactions involve spatially restricted expression of several, teeth-related genes and the secretion of various transcription and signaling factors.

View Article: PubMed Central - PubMed

Affiliation: University of Athens, Faculty of Biology, Department of Cell Biology and Biophysics, Athens, Greece.

ABSTRACT
The ancestor of recent vertebrate teeth was a tooth-like structure on the outer body surface of jawless fishes. Over the course of 500,000,000 years of evolution, many of those structures migrated into the mouth cavity. In addition, the total number of teeth per dentition generally decreased and teeth morphological complexity increased. Teeth form mainly on the jaws within the mouth cavity through mutual, delicate interactions between dental epithelium and oral ectomesenchyme. These interactions involve spatially restricted expression of several, teeth-related genes and the secretion of various transcription and signaling factors. Congenital disturbances in tooth formation, acquired dental diseases and odontogenic tumors affect millions of people and rank human oral pathology as the second most frequent clinical problem. On the basis of substantial experimental evidence and advances in bioengineering, many scientists strongly believe that a deep knowledge of the evolutionary relationships and the cellular and molecular mechanisms regulating the morphogenesis of a given tooth in its natural position, in vivo, will be useful in the near future to prevent and treat teeth pathologies and malformations and for in vitro and in vivo teeth tissue regeneration.

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Stages in teeth development: (A) Pre-patterned oral ectoderm is in close contact with cranial, neural crest ectomesenchyme. At this stage (ED 10) the odontogenic potential resides in the epithelium. (B) The epithelial cells secrete specific signals in different areas, proliferate and form a band of epithelial tissue, the dental lamina and the dental placodes. (C) At the sites of the dental placodes the epithelial cells proliferate and intrude within the mesenchyme forming the tooth buds. At this developmental stage the odontogenic potential is lost form the epithelium and granted to the ectomesenchyme. (D) The bud folds in and acquires initially the form of an inverted cap and later the form of a bell (E). [cl = cervical loop, iee = inner enamel epithelium, oee = outer enamel epithelium, pek = primary enamel knot, sek = secondary enamel knots].
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Figure 4: Stages in teeth development: (A) Pre-patterned oral ectoderm is in close contact with cranial, neural crest ectomesenchyme. At this stage (ED 10) the odontogenic potential resides in the epithelium. (B) The epithelial cells secrete specific signals in different areas, proliferate and form a band of epithelial tissue, the dental lamina and the dental placodes. (C) At the sites of the dental placodes the epithelial cells proliferate and intrude within the mesenchyme forming the tooth buds. At this developmental stage the odontogenic potential is lost form the epithelium and granted to the ectomesenchyme. (D) The bud folds in and acquires initially the form of an inverted cap and later the form of a bell (E). [cl = cervical loop, iee = inner enamel epithelium, oee = outer enamel epithelium, pek = primary enamel knot, sek = secondary enamel knots].

Mentions: As the neural tube forms, the dorsal ectoderm synthesizes the signaling protein WNT6; whereas, in the neural plate, members of the BMPs family are produced. Where these two embryonic tissues intersect, active cell multiplication occurs in both the ectoderm and neuroderm. These multiplying cells express the FOXD3 gene, which instructs these cells to form two dorsal, longitudinal rows of ectomesenchyme on both sides of the neural tube to create a transient population of highly nomadic cells, the neural crest cells. The embryonic brain is subdivided into the forebrain, midbrain and hindbrain (rhombencephalon), which is further subdivided into eight rhombomeres (R1-R8, Fig. 3). The archenteron continues to develop in a posterior to anterior direction and participates in pharyngeal arch formation. The pharyngeal arches contain a central blood vessel, the aortic arch, surrounded by paraxial mesoderm. This core is enveloped by a sheet of cnc cells; this cells, in their turn, are covered by continuous sheets of epidermal ectoderm and internal endoderm. The first pharyngeal arch forms the upper and the lower jaws. Massive layers of the oropharyngeal epithelium (stomodeum) migrate over and overlap the pharyngeal arches; odontogenic cells from the neural crest have already migrated and populated the region by this time. Although oral teeth are thought to arise exclusively from the ectoderm, pharyngeal teeth may also be derived from the endoderm epithelium 9, 20, 21. Cranial neural crest (cnc) cells, although of ectodermal origin, undergo “mesenchymalization,” a process justifying their designation as ectomesenchymal cells 46. Interestingly, before the onset of their migration, the cnc cells express Hox genes; after arrival at their destination places (first pharyngeal arch), they do not express Hox genes. This fact suggests that the acquired identity is maintained 46. Some of the cnc cells from the forebrain region migrate ventrally between the surface ectoderm and local mesoderm and establish the frontonasal prominence, where upper incisors form. Cranial neural crest cells from the midbrain and the three first rhombomeres populate the first pharyngeal arch, where all other teeth develop on the rest of the maxilla and the whole mandible. The homeobox genes LHX6 and LHX7 appear to have critical roles in directing the cnc cells to their correct destinations 47. There, the cnc cells multiply actively to produce the main body of the pharyngeal arch. Upon arrival and arrangement of the cnc cells, teeth develop by multiple, reciprocal, inductive molecular interactions between the dental epithelium (perhaps with cranial paraxial mesoderm and endoderm too) and the underlying ectomesenchyme in the maxilla and mandible (Fig. 4a) 8.


A curriculum vitae of teeth: evolution, generation, regeneration.

Koussoulakou DS, Margaritis LH, Koussoulakos SL - Int. J. Biol. Sci. (2009)

Stages in teeth development: (A) Pre-patterned oral ectoderm is in close contact with cranial, neural crest ectomesenchyme. At this stage (ED 10) the odontogenic potential resides in the epithelium. (B) The epithelial cells secrete specific signals in different areas, proliferate and form a band of epithelial tissue, the dental lamina and the dental placodes. (C) At the sites of the dental placodes the epithelial cells proliferate and intrude within the mesenchyme forming the tooth buds. At this developmental stage the odontogenic potential is lost form the epithelium and granted to the ectomesenchyme. (D) The bud folds in and acquires initially the form of an inverted cap and later the form of a bell (E). [cl = cervical loop, iee = inner enamel epithelium, oee = outer enamel epithelium, pek = primary enamel knot, sek = secondary enamel knots].
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Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2651620&req=5

Figure 4: Stages in teeth development: (A) Pre-patterned oral ectoderm is in close contact with cranial, neural crest ectomesenchyme. At this stage (ED 10) the odontogenic potential resides in the epithelium. (B) The epithelial cells secrete specific signals in different areas, proliferate and form a band of epithelial tissue, the dental lamina and the dental placodes. (C) At the sites of the dental placodes the epithelial cells proliferate and intrude within the mesenchyme forming the tooth buds. At this developmental stage the odontogenic potential is lost form the epithelium and granted to the ectomesenchyme. (D) The bud folds in and acquires initially the form of an inverted cap and later the form of a bell (E). [cl = cervical loop, iee = inner enamel epithelium, oee = outer enamel epithelium, pek = primary enamel knot, sek = secondary enamel knots].
Mentions: As the neural tube forms, the dorsal ectoderm synthesizes the signaling protein WNT6; whereas, in the neural plate, members of the BMPs family are produced. Where these two embryonic tissues intersect, active cell multiplication occurs in both the ectoderm and neuroderm. These multiplying cells express the FOXD3 gene, which instructs these cells to form two dorsal, longitudinal rows of ectomesenchyme on both sides of the neural tube to create a transient population of highly nomadic cells, the neural crest cells. The embryonic brain is subdivided into the forebrain, midbrain and hindbrain (rhombencephalon), which is further subdivided into eight rhombomeres (R1-R8, Fig. 3). The archenteron continues to develop in a posterior to anterior direction and participates in pharyngeal arch formation. The pharyngeal arches contain a central blood vessel, the aortic arch, surrounded by paraxial mesoderm. This core is enveloped by a sheet of cnc cells; this cells, in their turn, are covered by continuous sheets of epidermal ectoderm and internal endoderm. The first pharyngeal arch forms the upper and the lower jaws. Massive layers of the oropharyngeal epithelium (stomodeum) migrate over and overlap the pharyngeal arches; odontogenic cells from the neural crest have already migrated and populated the region by this time. Although oral teeth are thought to arise exclusively from the ectoderm, pharyngeal teeth may also be derived from the endoderm epithelium 9, 20, 21. Cranial neural crest (cnc) cells, although of ectodermal origin, undergo “mesenchymalization,” a process justifying their designation as ectomesenchymal cells 46. Interestingly, before the onset of their migration, the cnc cells express Hox genes; after arrival at their destination places (first pharyngeal arch), they do not express Hox genes. This fact suggests that the acquired identity is maintained 46. Some of the cnc cells from the forebrain region migrate ventrally between the surface ectoderm and local mesoderm and establish the frontonasal prominence, where upper incisors form. Cranial neural crest cells from the midbrain and the three first rhombomeres populate the first pharyngeal arch, where all other teeth develop on the rest of the maxilla and the whole mandible. The homeobox genes LHX6 and LHX7 appear to have critical roles in directing the cnc cells to their correct destinations 47. There, the cnc cells multiply actively to produce the main body of the pharyngeal arch. Upon arrival and arrangement of the cnc cells, teeth develop by multiple, reciprocal, inductive molecular interactions between the dental epithelium (perhaps with cranial paraxial mesoderm and endoderm too) and the underlying ectomesenchyme in the maxilla and mandible (Fig. 4a) 8.

Bottom Line: Over the course of 500,000,000 years of evolution, many of those structures migrated into the mouth cavity.In addition, the total number of teeth per dentition generally decreased and teeth morphological complexity increased.These interactions involve spatially restricted expression of several, teeth-related genes and the secretion of various transcription and signaling factors.

View Article: PubMed Central - PubMed

Affiliation: University of Athens, Faculty of Biology, Department of Cell Biology and Biophysics, Athens, Greece.

ABSTRACT
The ancestor of recent vertebrate teeth was a tooth-like structure on the outer body surface of jawless fishes. Over the course of 500,000,000 years of evolution, many of those structures migrated into the mouth cavity. In addition, the total number of teeth per dentition generally decreased and teeth morphological complexity increased. Teeth form mainly on the jaws within the mouth cavity through mutual, delicate interactions between dental epithelium and oral ectomesenchyme. These interactions involve spatially restricted expression of several, teeth-related genes and the secretion of various transcription and signaling factors. Congenital disturbances in tooth formation, acquired dental diseases and odontogenic tumors affect millions of people and rank human oral pathology as the second most frequent clinical problem. On the basis of substantial experimental evidence and advances in bioengineering, many scientists strongly believe that a deep knowledge of the evolutionary relationships and the cellular and molecular mechanisms regulating the morphogenesis of a given tooth in its natural position, in vivo, will be useful in the near future to prevent and treat teeth pathologies and malformations and for in vitro and in vivo teeth tissue regeneration.

Show MeSH
Related in: MedlinePlus