title: Tooth and scale morphogenesis in shark: an alternative process to the mammalian enamel knot system.
abstract: BACKGROUND
  The gene regulatory network involved in tooth morphogenesis has been extremely well described in mammals and its modeling has allowed predictions of variations in regulatory pathway that may have led to evolution of tooth shapes. However, very little is known outside of mammals to understand how this regulatory framework may also account for tooth shape evolution at the level of gnathostomes. In this work, we describe expression patterns and proliferation/apoptosis assays to uncover homologous regulatory pathways in the catshark Scyliorhinus canicula.
  
  
  RESULTS
  Because of their similar structural and developmental features, gene expression patterns were described over the four developmental stages of both tooth and scale buds in the catshark. These gene expression patterns differ from mouse tooth development, and discrepancies are also observed between tooth and scale development within the catshark. However, a similar nested expression of Shh and Fgf suggests similar signaling involved in morphogenesis of all structures, although apoptosis assays do not support a strictly equivalent enamel knot system in sharks. Similarities in the topology of gene expression pattern, including Bmp signaling pathway, suggest that mouse molar development is more similar to scale bud development in the catshark.
  
  
  CONCLUSIONS
  These results support the fact that no enamel knot, as described in mammalian teeth, can be described in the morphogenesis of shark teeth or scales. However, homologous signaling pathways are involved in growth and morphogenesis with variations in their respective expression patterns. We speculate that variations in this topology of expression are also a substrate for tooth shape evolution, notably in regulating the growth axis and symmetry of the developing structure.
authors.affiliation: Institut des Sciences de l'Evolution de Montpellier, UMR5554, Université Montpellier, CNRS, IRD, EPHE, Montpellier, France. mdebiais@univ-montp2.fr.
authors.forename: Mélanie
authors.initials: M
authors.lastname: Debiais-Thibaud
authors.affiliation: Evolution, Génomes, Comportement & Ecologie, CNRS, IRD, Univ.Paris-Sud, Université Paris-Saclay, 91198, Gif-sur-Yvette, France. roxane.chiori@wanadoo.fr.|Université Paris Diderot, Sorbonne Paris Cité, Paris, France. roxane.chiori@wanadoo.fr.
authors.forename: Roxane
authors.initials: R
authors.lastname: Chiori
authors.affiliation: Institut des Sciences de l'Evolution de Montpellier, UMR5554, Université Montpellier, CNRS, IRD, EPHE, Montpellier, France. senault@univ-montp2.fr.
authors.forename: Sébastien
authors.initials: S
authors.lastname: Enault
authors.affiliation: Institut des Sciences de l'Evolution de Montpellier, UMR5554, Université Montpellier, CNRS, IRD, EPHE, Montpellier, France. silvan.oulion@gmail.com.
authors.forename: Silvan
authors.initials: S
authors.lastname: Oulion
authors.affiliation: Evolution, Génomes, Comportement & Ecologie, CNRS, IRD, Univ.Paris-Sud, Université Paris-Saclay, 91198, Gif-sur-Yvette, France. isabelle.Germon@egce.cnrs-gif.fr.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Germon
authors.affiliation: Institut des Sciences de l'Evolution de Montpellier, UMR5554, Université Montpellier, CNRS, IRD, EPHE, Montpellier, France. Camille.Martinand-Mari@univ-montp2.fr.
authors.forename: Camille
authors.initials: C
authors.lastname: Martinand-Mari
authors.affiliation: Evolution, Génomes, Comportement & Ecologie, CNRS, IRD, Univ.Paris-Sud, Université Paris-Saclay, 91198, Gif-sur-Yvette, France. Didier.Casane@egce.cnrs-gif.fr.|Université Paris Diderot, Sorbonne Paris Cité, Paris, France. Didier.Casane@egce.cnrs-gif.fr.
authors.forename: Didier
authors.initials: D
authors.lastname: Casane
authors.affiliation: Evolution, Génomes, Comportement & Ecologie, CNRS, IRD, Univ.Paris-Sud, Université Paris-Saclay, 91198, Gif-sur-Yvette, France. Veronique.Borday-Birraux@egce.cnrs-gif.fr.|Université Paris Diderot, Sorbonne Paris Cité, Paris, France. Veronique.Borday-Birraux@egce.cnrs-gif.fr.
authors.forename: Véronique
authors.initials: V
authors.lastname: Borday-Birraux
mesh_terms: D000825:Animal Structures / Q000166:cytology / Q000196:embryology*; D000818:Animals; D017209:Apoptosis; D005075:Biological Evolution; D019521:Body Patterning / Q000235:genetics; D049109:Cell Proliferation; D003743:Dental Enamel / Q000196:embryology*; D004848:Epithelium / Q000378:metabolism; D005346:Fibroblast Growth Factors / Q000235:genetics / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D008297:Male; D008322:Mammals / Q000196:embryology*; D008648:Mesoderm / Q000196:embryology / Q000378:metabolism; D051379:Mice; D008954:Models, Biological; D008963:Molar / Q000196:embryology; D009024:Morphogenesis; D012754:Sharks / Q000196:embryology*; D014070:Tooth / Q000033:anatomy & histology / Q000166:cytology / Q000196:embryology*
chemical_list: D005346:Fibroblast Growth Factors