Meeting Abstract
S1.3 Monday, Jan. 4 Amphioxus thyroid hormone signaling pathway and the evolution of metamorphosis in chordates PARIS, M*; ESCRIVA, H; SCHUBERT, M; BRUNET, F; BRTKO, J; CIESIELSKI, F; JAMIN, E; CRAVEDI, JP; RENAUD, JP; SCANLAN, TS; HOLLAND, ND; LAUDET, V; Univ. of California, Berkeley; Lab. Arago, Banyuls sur mer; Ecole Normale Superieure de Lyon; Ecole Normale Superieure de Lyon; Inst. of Experimental Endocrinology; AliX, Illkirch; INRA, Toulouse; INRA, Toulouse; AliX, Illkirch; Oregon Health and Science Univ., Portland; Scripps Inst. of Oceanography, La Jolla; Ecole Normale Superieure de Lyon mparis@berkeley.edu
Metamorhposis is a spectacular post-embryonic developmental stage, allowing a larva to become a juvenile. In the chordate lineage, that comprises vertebrates, urochordates like tunicates and cephalochordates like amphioxus, the morphological changes during larva-to-adult transitions vary extensively from one species to another, suggesting that metamorphosis may have arisen several times in the chordate lineage. Does the molecular determinism of metamorphosis in this group reflect this morphological diversity? In the well-studied vertebrates, metamorphosis is triggered by thyroid hormones (THs) binding to their receptor TR, member of the nuclear hormone receptor superfamily. In order to get better insight into the evolution of the molecular determinism of metamorphosis in chordates, we focused on the most basal chordate amphioxus. Combined biochemical and phylogenetic approaches allowed us to establish that amphioxus produces various THs through metabolic pathways homologous to vertebrate ones. Then we showed that TH production as well as TH-dependent TR activation are essential for metamorphosis induction in amphioxus, like in vertebrates, with the slight difference that the active TH is not T3, the classical vertebrate TH, but possibly its derivative TRIAC. Consequently the homology of metamorphosis in chordates is revealed by the conservation of its triggering mechanism. This suggests that the evolution of metamorphosis in chordates is marked by the conservation of the couple TH/TR whereas other parts of the regulatory network may change to underlie the morphological diversity observed nowadays.
