Ultrastructure and biochemistry of the light-emitting system of lantern shark (Etmopterus spinax) photophores
(2014)
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- Authors
- Supervisors
- Mallefet, Jérôme
- Abstract
- Bioluminescence, i.e. the ability for living organisms to emit light, is a widespread phenomenon in deep-ocean, due to valuable ecological advantages it provides to organisms endowed with this capability. Six percent of deep-sea cartilaginous fishes (sharks, rays, skates and chimaeras) are luminous. Among them, the lantern shark Etmopterus spinax Linnaeus, 1758 is one of the most commons and can be easily caught. For this reason, it has recently become a model species for studying bioluminescence in shark. Although various aspects (functions and control) of this complex phenomenon are now better understood in this species, the photocyte (i.e. the light-emitting cell) mechanism of light emission remains unsolved. This is the subject addressed in this work. In the first chapter, photophore ultrastructure is explored since it is a key step in investigating an unknown bioluminescent mechanism. By using transmission electron microscopy (TEM), we were able to describe photophore fine organization (Paper 1): a new structure, a reflector, which was believed to be absent in shark photophores, was highlighted. Photocytes were found to be divided into three distinct areas, of which the apical one, oriented toward the photophore center and containing numerous granular inclusions, was proved to be the light-emitting area (Paper 2). By investigating photocyte ultrastructural changes during the course of a lightemission event, we proved granular inclusion to represent shark microsource (i.e. the intracellular light-emitting site, where the chemiluminescent reaction takes place), and we proposed the term “glowon” to characterize this novel particle (Paper 2). In the second chapter, we addressed E. spinax feeding habits in order to identify putative luminous preys and analyze whether the shark could obtain a known luciferin (i.e. the luminous substrate) through its diet and use it for its own light production. The results we obtained (Paper 3) suggested E. spinax does not use a known luciferin but might rather use a novel molecule as substrate or an unknown storage or active form of a known luciferin. The isolation and purification of putative new luminous molecules (luciferin and luciferase –i.e. the reaction enzyme) are initiated in the third chapter of which the purpose is to provide basis experiments and reflection for the future complete characterization of this system. Finally, all results were integrated and discussed together with regard to previous findings on bioluminescence functions and control in this shark species.
- Affiliations
UCLouvain SST/ELI/ELIB - Biodiversity
Citations
Renwart, M. (2014). Ultrastructure and biochemistry of the light-emitting system of lantern shark (Etmopterus spinax) photophores. https://hdl.handle.net/2078.5/193260