An amphioxus orthologue of the estrogen receptor that does not bind estradiol: Insights into estrogen receptor evolution

Mathilde Paris¹ , Katarina Pettersson² , Michael Schubert¹ , Stephanie Bertrand³ , Ingemar Pongratz² , Hector Escriva³ and Vincent Laudet¹

¹Institut de Génomique Fonctionnelle de Lyon, Molecular Zoology team, Université de Lyon, Ecole Normale Supérieure de Lyon, Université Lyon 1, CNRS, INRA, Institut Fédératif 128 Biosciences Gerland Lyon Sud, France

²Karolinska Institutet, Department of Biosciences and Nutrition, S-141 57 Huddinge, Sweden

³CNRS, UMR 7628, Modèles en Biologie Cellulaire et Evolutive, Observatoire océanographique, F-66651, Banyuls/mer, France

author email corresponding author email

BMC Evolutionary Biology 2008, 8:219doi:10.1186/1471-2148-8-219


Published:	25 July 2008

Abstract

Background

The origin of nuclear receptors (NRs) and the question whether the ancestral NR was a liganded or an unliganded transcription factor has been recently debated. To obtain insight into the evolution of the ligand binding ability of estrogen receptors (ER), we comparatively characterized the ER from the protochordate amphioxus (Branchiostoma floridae), and the ER from lamprey (Petromyzon marinus), a basal vertebrate.

Results

Extensive phylogenetic studies as well as signature analysis allowed us to confirm that the amphioxus ER (amphiER) and the lamprey ER (lampER) belong to the ER group. LampER behaves as a "classical" vertebrate ER, as it binds to specific DNA Estrogen Responsive Elements (EREs), and is activated by estradiol (E₂), the classical ER natural ligand. In contrast, we found that although amphiER binds EREs, it is unable to bind E₂and to activate transcription in response to E₂. Among the 7 natural and synthetic ER ligands tested as well as a large repertoire of 14 cholesterol derivatives, only Bisphenol A (an endocrine disruptor with estrogenic activity) bound to amphiER, suggesting that a ligand binding pocket exists within the receptor. Parsimony analysis considering all available ER sequences suggest that the ancestral ER was not able to bind E₂and that this ability evolved specifically in the vertebrate lineage. This result does not support a previous analysis based on ancestral sequence reconstruction that proposed the ancestral steroid receptor to bind estradiol. We show that biased taxonomic sampling can alter the calculation of ancestral sequence and that the previous result might stem from a high proportion of vertebrate ERs in the dataset used to compute the ancestral sequence.

Conclusion

Taken together, our results highlight the importance of comparative experimental approaches vs ancestral reconstructions for the evolutionary study of endocrine systems: comparative analysis of extant ERs suggests that the ancestral ER did not bind estradiol and that it gained the ability to be regulated by estradiol specifically in the vertebrate lineage, before lamprey split.