ZFIN ID: ZDB-PUB-060719-16
Developmental genetic mechanisms of evolutionary tooth loss in cypriniform fishes
Stock, D.W., Jackman, W.R., and Trapani, J.
Date: 2006
Source: Development (Cambridge, England)   133(16): 3127-3137 (Journal)
Registered Authors: Jackman, William (Bill), Stock, David W.
Keywords: Zebrafish, Astyanax, Medaka, Catfish, Dlx, Fgf, Constraint
MeSH Terms:
  • Amino Acid Sequence
  • Animals
  • Biological Evolution*
  • Cypriniformes/genetics*
  • Cypriniformes/growth & development*
  • Epithelium/metabolism
  • Fibroblast Growth Factors/antagonists & inhibitors
  • Fibroblast Growth Factors/metabolism
  • Homeodomain Proteins/genetics
  • Homeodomain Proteins/metabolism
  • Molecular Sequence Data
  • Mouth Mucosa/metabolism
  • PAX9 Transcription Factor/genetics
  • PAX9 Transcription Factor/metabolism
  • Signal Transduction
  • Tooth Loss/genetics*
  • Transcription Factors/genetics
  • Transcription Factors/metabolism
  • Zebrafish/genetics
  • Zebrafish/growth & development*
PubMed: 16831836 Full text @ Development
The fossil record indicates that cypriniform fishes, a group including the zebrafish, lost oral teeth over 50 million years ago. Despite subsequent diversification of feeding modes, no cypriniform has regained oral teeth, suggesting the zebrafish as a model for studying the developmental genetic basis of evolutionary constraint. To investigate the mechanism of cypriniform tooth loss, we compared the oral expression of seven genes whose mammalian orthologs are involved in tooth initiation in the zebrafish and the Mexican tetra, Astyanax mexicanus, a related species retaining oral teeth. The most significant difference we found was an absence in zebrafish oral epithelium of expression of dlx2a and dlx2b, transcription factors that are expressed in early Astyanax odontogenic epithelium. Analysis of orthologous genes in the Japanese medaka (Oryzias latipes) and a catfish (Synodontis multipunctatus) suggests that expression was lost in cypriniforms, rather than gained in Astyanax. Treatment of Astyanax with an inhibitor of Fibroblast growth factor (Fgf) signaling produced a partial phenocopy of the zebrafish oral region, in that oral teeth, and expression of dlx2a and dlx2b, were lost, whereas shh and pitx2, genes whose expression is present in zebrafish oral epithelium, were unaffected. We hypothesize that a loss of Fgf signaling to oral epithelium was associated with cypriniform tooth loss.