Biology

Prof. Deborah M Power
Universidade do Algarve, Faro, Portugal

The flatfish (Pleuronectiformes) are a group of teleosts that suffer a profound change in morphology during the larval to juvenile transition. In all flatfish this metamorphosis is associated with a shift from symmetry to asymmetry and this event is driven by the thyroid hormones (THs) and inevitably involves the central hypothalamus-pituitary-thyroid (HPA) axis and also the elements of the thyroid axis in the periphery. There is increasing molecular evidence suggesting that flatfish are polyphyletic and do not all descend from a common ancestor with the Psettodes (eg. Indian halibut, spiny turbot) being clustered with non-flatfish (Campbell et al., Mol. Phylog. & Evol. 2013). Studies of Amphistium and Heteronectes, extinct, spiny-finned fishes from the Eocene epoch, indicate that acquisition of cranial asymmetry in flatfish was gradual (Friedman, Nature, 2008) and raises questions about when the thyroid hormones were recruited to this process. The evolutionary trajectory of the flatfish makes them an interesting model for investigating how evolutionary pressure has shaped metamorphosis, and presumably also thyroid axis evolution. The recent release of the Chinese tongue sole (Cynoglossus semilaevis; Chen, et al. Nat Genet 2014) genome and the publicly available genome and transcriptome sequences of other flatfish, such as the Senegalese sole (Solea senegalensis), Atlantic halibut (Hippoglossus hippoglossus), Japanese flounder (Paralichthys olivaceus) and the turbot (Scophthalmus maximus) represent a resource that is providing important insights into gene evolution and in particular genes of the thyroid axis. By focusing on metamorphosis related changes in specific tissue systems we are gaining insight into how a single hormone can be responsible for such a diversity of changes.

Acknowledgements: Strategic funding from the Portuguese Science Foundation (FCT, UID/Multi/04326/2013) and from an Fp7 research project (LIFECYCLE No. 222719).