Xenopus Pax-2/5/8 orthologues: novel insights into Pax gene evolution and identification of Pax-8 as the earliest marker for otic and pronephric cell lineages

Dev Genet. 1999;24(3-4):208-19. doi: 10.1002/(SICI)1520-6408(1999)24:3/4<208::AID-DVG4>3.0.CO;2-J.


Pax genes are a family of transcription factors playing fundamental roles during organogenesis. We have recently demonstrated the expression of Pax-2 during Xenopus embryogenesis [Heller N, Brändli AW (1997): Mech Dev 69: 83-104]. Here we report the cloning and characterization of Xenopus Pax-5 and Pax-8, two orthologues of the Pax-2/5/8 gene family. Molecular phylogenetic analysis indicates that the amphibian Pax-2/5/8 genes are close relatives of their mammalian counterparts and that all vertebrate Pax-2/5/8 genes are derived from a single ancestral gene. Xenopus Pax-2/5/8 genes are expressed in spatially and temporally overlapping patterns during development of at least seven distinct tissues. Most strikingly, Xenopus Pax-8 was identified as the earliest marker of the prospective otic placode and of the intermediate mesoderm, indicating that Pax-8 may play a central role in auditory and excretory system development. Comparison of the expression patterns of fish, amphibian, and mammalian Pax-2/5/8 genes revealed that the tissue specificity of Pax-2/5/8 gene family expression is overall evolutionarily conserved. The expression domains of individual orthologues can however vary in a species-specific manner. For example, the thyroid glands of mammals express Pax-8, while in Xenopus Pax-2 is expressed instead. Our findings indicate that differential silencing of Pax-2/5/8 gene expression may have occurred after the different classes of vertebrates began to evolve separately.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Base Sequence
  • Cloning, Molecular
  • Conserved Sequence
  • DNA, Complementary / genetics
  • DNA-Binding Proteins / genetics*
  • Ear, Inner / embryology
  • Evolution, Molecular
  • Gene Expression Regulation, Developmental
  • Kidney / embryology
  • Molecular Sequence Data
  • Multigene Family
  • Nuclear Proteins / genetics*
  • PAX2 Transcription Factor
  • PAX5 Transcription Factor
  • PAX8 Transcription Factor
  • Paired Box Transcription Factors
  • Phylogeny
  • Sequence Homology, Amino Acid
  • Species Specificity
  • Thyroid Gland / embryology
  • Trans-Activators / genetics*
  • Transcription Factors / genetics*
  • Xenopus / embryology*
  • Xenopus / genetics*
  • Xenopus Proteins


  • DNA, Complementary
  • DNA-Binding Proteins
  • Nuclear Proteins
  • PAX2 Transcription Factor
  • PAX5 Transcription Factor
  • PAX8 Transcription Factor
  • Paired Box Transcription Factors
  • Pax8 protein, Xenopus
  • Trans-Activators
  • Transcription Factors
  • Xenopus Proteins
  • pax5 protein, Xenopus

Associated data

  • GENBANK/AJ010503
  • GENBANK/AJ010504