Amphioxus postembryonic development reveals the homology of chordate metamorphosis.
Most studies in evolution are centered on how homologous genes, structures, and/or processes appeared and diverged. Although historical homology is well defined as a concept, in practice its establishment can be problematic, especially for some morphological traits or developmental processes. Metamorphosis in chordates is such an enigmatic character. Defined as a spectacular postembryonic larva-to-adult transition, it shows a wide morphological diversity between the different chordate lineages, suggesting that it might have appeared several times independently. In vertebrates, metamorphosis is triggered by binding of the thyroid hormones (THs) T(4) and T(3) to thyroid-hormone receptors (TRs). Here we show that a TH derivative, triiodothyroacetic acid (TRIAC), induces metamorphosis in the cephalochordate amphioxus. The amphioxus TR (amphiTR) mediates spontaneous and TRIAC-induced metamorphosis because it strongly binds to TRIAC, and a specific TR antagonist, NH3, inhibits both spontaneous and TRIAC-induced metamorphosis. Moreover, as in amphibians, amphiTR expression levels increase around metamorphosis and are enhanced by THs. Therefore, TH-regulated metamorphosis, mediated by TR, is an ancestral feature of all chordates. This conservation of a regulatory network supports the homology of metamorphosis in the chordate lineage.
Institut de Génomique Fonctionnelle de Lyon, Université de Lyon, CNRS, INRA, UCB Lyon 1, IFR128 Lyon Biosciences, Ecole Normale Supérieure de Lyon, 69364 Lyon Cedex 07, France.
Mathilde
M
Paris
Hector
H
Escriva
Michael
M
Schubert
Frédéric
F
Brunet
Julius
J
Brtko
Fabrice
F
Ciesielski
Dominique
D
Roecklin
Valérie
V
Vivat-Hannah
Emilien L
EL
Jamin
Jean-Pierre
JP
Cravedi
Thomas S
TS
Scanlan
Jean-Paul
JP
Renaud
Nicholas D
ND
Holland
Vincent
V
Laudet
D000818:Animals; D005075:Biological Evolution; D002816:Chordata, Nonvertebrate / Q000254:growth & development*; D008675:Metamorphosis, Biological / Q000502:physiology*; D011988:Receptors, Thyroid Hormone / Q000502:physiology*; D013963:Thyroid Hormones / Q000502:physiology*
D011988:Receptors, Thyroid Hormone; D013963:Thyroid Hormones