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The origin of evolutionary novelties: regulation of Hoxd genes and the evolutionary transition from fish fins to tetrapod limbs

Final Report Summary - LIMB EVOLUTION (The origin of evolutionary novelties: regulation of Hoxd genes and the evolutionary transition from fish fins to tetrapod limbs)

Ever since Darwin, the evolution of limbs have been a topic of major interest to the scientific community and society. Fossil data suggests that limbs evolved from fish fins by sequential elaboration of their distal endoskeleton, giving rise to the autopod (hand) close to the tetrapod origin. This important morphological transformation allowed the successful adaptation of tetrapods to the land environment in the Devonian. It has been proposed that the acquisition of novel enhancers potentiated the distal expansion of 5'Hoxd genes in fins, causing developmental changes that served as substrate for the distal elaboration of the limb endoskeleton. However, this hypothesis has never been tested before this project and the published information about this crucial evolutionary transformation was essentially speculative. With the conditions offered by the Marie Curie Intra-European Fellowship (IEF), we first attempt to explain the real role of Hox genes in the fin-to-limb transition. We have shown that a Hoxd13 enhancer region specific of tetrapods acts similarly during zebrafish fin development. This suggests that the trans-regulators for this enhancer are conserved between fishes and tetrapods. Moreover, by performing gain of function assays, we have shown a clear association between Hoxd13 levels and the morphologies expected during the fin-to-limb transition, which is truly spectacular. Analyses of molecular markers after the gain of function experiments suggested that the downstream Hoxd gene network required for these distal endoskeletal elaborations are present in zebrafish. Therefore, we infer that the last common ancestor of teleosts and tetrapods was already poised to expand the chondrogenic tissue distally. The acquisition of novel enhancers might have sufficed to initiate this process. These are major finding to the field and the first association between Hoxd regulation and the evolution of limbs. We are know trying to publish this solid piece of work in a high impact journal and we are looking forward how its widespread disclosure will 'contaminate' several fields of knowledge and inspiring functional experimentation to address, with out any fears, classical evolutionary questions.

Societal implications of the project

To assure that the European Union (EU) has sufficient high quality human resources in the research field is essential to European future competitiveness and economic growth. The current project offered a European fellow the possibility to carry out research in Europe and it will make possible transference of expertise, especially dealing with the zebrafish model, to her own country (Portugal). This fellowship also contributed to increase the international dimension and attractiveness of European research. This proposal covers several areas of research (functional genomics, developmental biology and evolution) and will clearly contribute to enhance EU scientific excellence.

The problem the applicant proposes to tackle in this proposal is a relevant and long-standing one, with high implications in the Life Sciences area. However, it has been only recently that a set of technologies, developed especially in Europe, became available allowing the ultimate functional testing of this question. Therefore, through the intra-European sharing of expertise during this project, we had the chance to address a profound question in biology, which will highly impact the scientific community and the academics throughout the world.

As an important 'side effect', candidate and hosts beneficiated from mutually cultural and scientific exchange, which stems from joint work, strengthens long-lasting collaborations.

We believe that this project will rapidly amplify its benefits having a significant impact in the society.