03 octobre 2019
Salle Jean-Baptiste Carnoy - Place Croix du Sud 4-5
Extraocular photoreception and bioluminescence of representatives of two luminous shark families, Etmopteridae and Dalatiidae
In the depths of our oceans, Etmopteridae and Dalatiidae, two luminous shark families, have evolved the ability to emit light. They emit a blue-green luminescence via light organs (i.e. photophores) to counterilluminate by mimicking the surrounding environmental light. Bioluminescence needs to be finely tuned to avoid being spotted by underneath predators. Although increasing cues on a hormonal control exist, the precise light emission mechanisms in these two families remains to be studied. Recently, some authors have hypothesized the implication of extraocular photoreceptors to regulate bioluminescence in other taxa (i.e. ctenophore, cephalopod or echinoderm). It has been assumed that across perception of their own light, these organisms could adjust the right intensity of their luminescence compared to the surrounding light.
By using Etmopteridae and Dalatiidae model species (Etmopterus spinax, E. molleri and Squaliolus aliae), this thesis deals with the hypothesis that a close link exists between light emission and perception at the photophore level. Results were obtained by techniques including transcriptome analysis, immunodetection, lumino-pharmacology, etc.
Results indicated that luminous sharks display extraocular opsins (Opn3) mainly located at the iris-like structure level (i.e. ILS, photophore shutter) allowing their luminescence perception. Actors such as (i) hormones, (ii) Opn3, (iii) G-protein coupled receptors, (iv) G-proteins, (v) cAMP, (vi) IP3, (vii) Ca2+, (viii) calmodulin, (ix) kinesin and (x) dynein, are involved in the mechanisms linking light emission and perception. These results highlight similarities between control to regulate photophore light outputs in luminous sharks and physiological color change regulation to adapt to background colors in epipelagic sharks. This thesis opens research lines aiming to decipher interactions between photoreception processes and pigment motion regulations as being a general feature to regulate bioluminescence in other taxa.
Jury members :
- Prof. Jérôme Mallefet (UCLouvain), supervisor
- Prof. Hans Van Dyck (UCLouvain), chaiperson
- Prof. Thierry Hance (UCLouvain), secretary
- Prof. René Rezsohazy (UCLouvain)
- Dr. Patrick Flammang (UMons)
- Dr. Jérôme Delroisse (UMons)
- Dr. Gavin Naylor (University of Floride, USA)