The origin of bilateral animals has been debated for more than a century. At the centre of this 
debate lays a discussion on the mechanisms that drove the transition from a radially symmetrical ancestor to a bilateral one. To a great extent, the proposed models for such a transition rests on the way basal bilaterians were imagined: morphologically simple or structurally complex. In the last 10-15 years, the prevalent view held that basal bilaterian groups no longer exist and that the last bilaterian ancestor was a rather complex organism. In 1999, however, Ruiz-Trillo et al. suggested that simple extant basal bilaterians do actually exist: the acoel flatworms.
In order to understand, mechanistically, how this important evolutionary transition took place we have taken a developmental approach. We are characterizing in the acoel worm Convoluta pulchra, specific families of developmental regulatory genes whose roles are well understood both in radial animals and in other, more advanced, bilaterians.
Staff
Prof. Jaume Baguñà
Dr. Pere Martínez
Predocs
Eduardo Moreno
Amandine Bery
Alexander Alsén
Marta Chiodin
Collaborators
Drs. Xavier Bailly i Patrick Cormier (Station Biologique Roscoff, France)
Prof. Glen Bristow (University of Bergen, Norway)
2) Splox, a ParaHox gene involved in sea urchin gut regionalization
Over the last few years we have isolated and characterized a new homeobox gene from the sea urchin Srongylocentrotus purpuratus. This gene is an orthologue of the Xenopus XlHbox8 and mouse IPF-1 ParaHox genes. We have called it Splox. It is expressed during embryogenesis reaching its maximum level at 48 h (late gastrula). At the mesenchyme blastula stage, Splox is expressed in the vegetal plate. No message is detected in the skeletogenic mesenchyme. Later, during gastrulation, the transcript is preferentially localized in both ends of the archenteron (mainly around the blastopore and in the foregut region). The archenteron expression has clearly an oral bias. Knock-out experiments have shown that in the absence of Splox, the foregut is not regionalized properly. The gene network involved in the specification of the different gut regions is unders study.
Staff
Dr. Pere Martínez
Predocs
Rossella Annunziata
Collaborators
Dr. Maria Ina Arnone (Stazione Zoologica, Napoli, Italy)
Montserrat Fernandez (Stazione Zoologica, Napoli, Italy)
3) Molecular basis of echinoderm arm, and CNS, regeneration
It has been shown in the few well-described cases of regeneration (some amphibians and flatworms) that those genes involved in the patterning of the major embryonic axes (mainly members of different classes of homeobox genes) are reused to pattern the regenerating structures.
In order to understand the role of homeobox-containing genes during regenerative processes in echinoderms we have isolated a complement of genes belonging to the Hox class that are expressed during this process in two major echinoderm groups: asteroids (Asterias rubens) and ophiouroids (Amphiura filiformis), both well known for their extraordinary capacity for regeneration.
By exploiting the sequence conservation of the homeobox, putative orthologues of several Hox genes belonging to the anterior, medial and posterior groups have been isolated. Recently in situ hybridizatio experiments have been started at KMF, Sweden.
We are also characterizing genes of the Wnt pathway in this biological system.
Staff
Dr. Pere Martínez
Collaborators
Prof. Michael Thorndyke (Kristineberg Marine Station, Royal Swedish Academy, Sweden)
Dr. Karen Wilson (Kristineberg Marine Station, Royal Swedish Academy, Sweden)
