title: Heterogeneous conservation of Dlx paralog co-expression in jawed vertebrates.
abstract: BACKGROUND
  The Dlx gene family encodes transcription factors involved in the development of a wide variety of morphological innovations that first evolved at the origins of vertebrates or of the jawed vertebrates. This gene family expanded with the two rounds of genome duplications that occurred before jawed vertebrates diversified. It includes at least three bigene pairs sharing conserved regulatory sequences in tetrapods and teleost fish, but has been only partially characterized in chondrichthyans, the third major group of jawed vertebrates. Here we take advantage of developmental and molecular tools applied to the shark Scyliorhinus canicula to fill in the gap and provide an overview of the evolution of the Dlx family in the jawed vertebrates. These results are analyzed in the theoretical framework of the DDC (Duplication-Degeneration-Complementation) model.
  
  
  RESULTS
  The genomic organisation of the catshark Dlx genes is similar to that previously described for tetrapods. Conserved non-coding elements identified in bony fish were also identified in catshark Dlx clusters and showed regulatory activity in transgenic zebrafish. Gene expression patterns in the catshark showed that there are some expression sites with high conservation of the expressed paralog(s) and other expression sites with events of paralog sub-functionalization during jawed vertebrate diversification, resulting in a wide variety of evolutionary scenarios within this gene family.
  
  
  CONCLUSIONS
  Dlx gene expression patterns in the catshark show that there has been little neo-functionalization in Dlx genes over gnathostome evolution. In most cases, one tandem duplication and two rounds of vertebrate genome duplication have led to at least six Dlx coding sequences with redundant expression patterns followed by some instances of paralog sub-functionalization. Regulatory constraints such as shared enhancers, and functional constraints including gene pleiotropy, may have contributed to the evolutionary inertia leading to high redundancy between gene expression patterns.
authors.affiliation: Institut des Sciences de l'Evolution, Université de Montpellier II, UMR5554, Montpellier, France.
authors.forename: Mélanie
authors.initials: M
authors.lastname: Debiais-Thibaud
authors.forename: Cushla J
authors.initials: CJ
authors.lastname: Metcalfe
authors.forename: Jacob
authors.initials: J
authors.lastname: Pollack
authors.forename: Isabelle
authors.initials: I
authors.lastname: Germon
authors.forename: Marc
authors.initials: M
authors.lastname: Ekker
authors.forename: Michael
authors.initials: M
authors.lastname: Depew
authors.forename: Patrick
authors.initials: P
authors.lastname: Laurenti
authors.forename: Véronique
authors.initials: V
authors.lastname: Borday-Birraux
authors.forename: Didier
authors.initials: D
authors.lastname: Casane
mesh_terms: D058500:Animal Fins / Q000196:embryology; D000818:Animals; D001921:Brain / Q000196:embryology; D001934:Branchial Region / Q000196:embryology; D017124:Conserved Sequence / Q000235:genetics*; D019143:Evolution, Molecular; D020440:Gene Duplication / Q000235:genetics; D015870:Gene Expression / Q000235:genetics; D018507:Gene Expression Regulation, Developmental / Q000235:genetics; D016678:Genome / Q000235:genetics; D018398:Homeodomain Proteins / Q000235:genetics*; D007568:Jaw / Q000196:embryology*; D009432:Neural Crest / Q000196:embryology; D010802:Phylogeny; D022661:RNA, Untranslated / Q000235:genetics; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics; D012754:Sharks / Q000196:embryology / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics*; D014714:Vertebrates / Q000196:embryology* / Q000235:genetics*; D015027:Zebrafish / Q000196:embryology / Q000235:genetics
chemical_list: C088334:Distal-less homeobox proteins; D018398:Homeodomain Proteins; D022661:RNA, Untranslated; D014157:Transcription Factors