title: Pattern and polarity in the development and evolution of the gnathostome jaw: both conservation and heterotopy in the branchial arches of the shark, Scyliorhinus canicula.
abstract: The acquisition of jaws constitutes a landmark event in vertebrate evolution, one that in large part potentiated their success and diversification. Jaw development and patterning involves an intricate spatiotemporal series of reciprocal inductive and responsive interactions between the cephalic epithelia and the cranial neural crest (CNC) and cephalic mesodermal mesenchyme. The coordinated regulation of these interactions is critical for both the ontogenetic registration of the jaws and the evolutionary elaboration of variable jaw morphologies and designs. Current models of jaw development and evolution have been built on molecular and cellular evidence gathered mostly in amniotes such as mice, chicks and humans, and augmented by a much smaller body of work on the zebrafish. These have been partnered by essential work attempting to understand the origins of jaws that has focused on the jawless lamprey. Chondrichthyans (cartilaginous fish) are the most distant group to amniotes within extant gnathostomes, and comprise the crucial clade uniting amniotes and agnathans; yet despite their critical phylogenetic position, evidence of the molecular and cellular underpinnings of jaw development in chondrichthyans is still lacking. Recent advances in genome and molecular developmental biology of the lesser spotted dogfish shark, Scyliorhinus canicula, make it ideal for the molecular study of chondrichthyan jaw development. Here, following the 'Hinge and Caps' model of jaw development, we have investigated evidence of heterotopic (relative changes in position) and heterochronic (relative changes in timing) shifts in gene expression, relative to amniotes, in the jaw primordia of S. canicula embryos. We demonstrate the presence of clear proximo-distal polarity in gene expression patterns in the shark embryo, thus establishing a baseline molecular baüplan for branchial arch-derived jaw development and further validating the utility of the 'Hinge and Caps' model in comparative studies of jaw development and evolution. Moreover, we correlate gene expression patterns with the absence of a lambdoidal junction (formed where the maxillary first arch meets the frontonasal processes) in chondrichthyans, further highlighting the importance of this region for the development and evolution of jaw structure in advanced gnathostomes.
authors.affiliation: Department of Craniofacial Development, King's College London, Floor 27, Guy's Hospital, London Bridge, London SE1 9RT, UK.
authors.forename: Claudia
authors.initials: C
authors.lastname: Compagnucci
authors.forename: Melanie
authors.initials: M
authors.lastname: Debiais-Thibaud
authors.forename: Marion
authors.initials: M
authors.lastname: Coolen
authors.forename: Jennifer
authors.initials: J
authors.lastname: Fish
authors.forename: John N
authors.initials: JN
authors.lastname: Griffin
authors.forename: Federica
authors.initials: F
authors.lastname: Bertocchini
authors.forename: Maryline
authors.initials: M
authors.lastname: Minoux
authors.forename: Filippo M
authors.initials: FM
authors.lastname: Rijli
authors.forename: Véronique
authors.initials: V
authors.lastname: Borday-Birraux
authors.forename: Didier
authors.initials: D
authors.lastname: Casane
authors.forename: Sylvie
authors.initials: S
authors.lastname: Mazan
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Depew
mesh_terms: D000367:Age Factors; D000818:Animals; D005075:Biological Evolution; D001934:Branchial Region / Q000196:embryology*; D017931:DNA Primers / Q000235:genetics; D004625:Embryo, Nonmammalian / Q000196:embryology / Q000648:ultrastructure; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D017403:In Situ Hybridization; D007568:Jaw / Q000033:anatomy & histology / Q000196:embryology*; D008855:Microscopy, Electron, Scanning; D008954:Models, Biological; D010802:Phylogeny; D012754:Sharks / Q000033:anatomy & histology / Q000196:embryology*; D013045:Species Specificity
chemical_list: D017931:DNA Primers