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.
Paris
Mathilde
M
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.
Escriva
Hector
H
Schubert
Michael
M
Brunet
Frédéric
F
Brtko
Julius
J
Ciesielski
Fabrice
F
Roecklin
Dominique
D
Vivat-Hannah
Valérie
V
Jamin
Emilien L
EL
Cravedi
Jean-Pierre
JP
Scanlan
Thomas S
TS
Renaud
Jean-Paul
JP
Holland
Nicholas D
ND
Laudet
Vincent
V
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