AmphiFoxE4, an amphioxus winged helix/forkhead gene encoding a protein closely related to vertebrate thyroid transcription factor-2: expression during pharyngeal development.
The full-length sequence and developmental expression of amphioxus AmphiFoxE4 are described. Transcripts of the gene are first detected in the pharyngeal endoderm, where the club-shaped gland is forming and subsequently in the definitive gland itself. AmphiFoxE4 is closely related to vertebrate genes encoding the thyroid-specific transcription factor-2 (TTF2), which plays an early developmental role in the morphogenesis of the thyroid gland and a later role in hormone-mediated control of thyroid function. In amphioxus, AmphiFoxE4 expression is not thyroid specific because the club-shaped gland, the only structure expressing the gene, is not homologous to the vertebrate thyroid; instead, the thyroid homologue of amphioxus is a specialized region of the pharyngeal endoderm called the endostyle. We propose that (a) the pharynx of an amphioxus-like ancestor of the vertebrates included a club-shaped gland that expressed FoxE4 as well as an endostyle that did not, and (b) the club-shaped gland soon disappeared in the vertebrate line of descent but (c) not before there was a homeogenetic transfer of FoxE4 expression from the club-shaped gland to the nearby endostyle. Such a transfer could have provided part of the genetic program enabling the endostyle to separate from the pharyngeal endoderm and migrate away as the rudiment of the thyroid gland.
Yu
Jr-Kai
JK
Marine Biology Research Division, Scripps Institution of Oceanography, La Jolla, CA 92093-0202, USA.
Holland
Linda Z
LZ
Jamrich
Milan
M
Blitz
Ira L
IL
Hollan
Nicholas D
ND
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002816:Chordata, Nonvertebrate / Q000033:anatomy & histology / Q000196:embryology / Q000235:genetics* / Q000502:physiology; D004247:DNA; D004268:DNA-Binding Proteins / Q000737:chemistry*; D019143:Evolution, Molecular; D051858:Forkhead Transcription Factors; D015870:Gene Expression; D005796:Genes; D008969:Molecular Sequence Data; D009024:Morphogenesis; D010614:Pharynx / Q000196:embryology; D012097:Repressor Proteins / Q000737:chemistry*; D013961:Thyroid Gland / Q000502:physiology; D014018:Tissue Distribution
D004268:DNA-Binding Proteins; C106894:FOXE1 protein, human; D051858:Forkhead Transcription Factors; D012097:Repressor Proteins; D004247:DNA