title: AmphiPax3/7, an amphioxus paired box gene: insights into chordate myogenesis, neurogenesis, and the possible evolutionary precursor of definitive vertebrate neural crest.
abstract: Amphioxus probably has only a single gene (AmphiPax3/7) in the Pax3/7 subfamily. Like its vertebrate homologs (Pax3 and Pax7), amphioxus AmphiPax3/7 is probably involved in specifying the axial musculature and muscularized notochord. During nervous system development, AmphiPax3/7 is first expressed in bilateral anteroposterior stripes along the edges of the neural plate. This early neural expression may be comparable to the transcription of Pax3 and Pax7 in some of the anterior neural crest cells of vertebrates. Previous studies by others and ourselves have demonstrated that several genes homologous to genetic markers for vertebrate neural crest are expressed along the neural plate-epidermis boundary in embryos of tunicates and amphioxus. Taken together, the early neural expression patterns of AmphiPax3/7 and other neural crest markers of amphioxus and tunicates suggest that cell populations that eventually gave rise to definitive vertebrate neural crest may have been present in ancestral invertebrate chordates. During later neurogenesis in amphioxus, AmphiPax3/7, like its vertebrate homologs, is expressed dorsally and dorsolaterally in the neural tube and may be involved in dorsoventral patterning. However, unlike its vertebrate homologs, AmphiPax3/7 is expressed only at the anterior end of the central nervous system instead of along much of the neuraxis; this amphioxus pattern may represent the loss of a primitive chordate character.
authors.affiliation: Marine Biology Research Division, Scripps Institution of Oceanography, La Jolla, CA 92093-0202, USA. lzholland@ucsd.edu
authors.forename: L Z
authors.initials: LZ
authors.lastname: Holland
authors.forename: M
authors.initials: M
authors.lastname: Schubert
authors.forename: Z
authors.initials: Z
authors.lastname: Kozmik
authors.forename: N D
authors.initials: ND
authors.lastname: Holland
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D005075:Biological Evolution; D002816:Chordata, Nonvertebrate / Q000196:embryology / Q000235:genetics*; D018076:DNA, Complementary; D004268:DNA-Binding Proteins / Q000235:genetics*; D018507:Gene Expression Regulation, Developmental; D018398:Homeodomain Proteins / Q000235:genetics*; D008969:Molecular Sequence Data; D009132:Muscles / Q000196:embryology*; D009420:Nervous System / Q000196:embryology*; D009432:Neural Crest; D000072041:PAX3 Transcription Factor; D051763:PAX7 Transcription Factor; D051761:Paired Box Transcription Factors; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors
chemical_list: D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D018398:Homeodomain Proteins; D000072041:PAX3 Transcription Factor; D051763:PAX7 Transcription Factor; D051761:Paired Box Transcription Factors; D014157:Transcription Factors; C068686:Pax3 protein, mouse