between 2 m depth), where a faint blue light remains 30– 32, a similar function was evolutionary put forward allowing bioluminescent organisms to hide from predation 33– 36. Chromatic countershading camouflage type may also be used in the same oceanic layer as predation support as exemplified in the tiger shark 29. between 0 and 200 m depth), many cephalopods 21– 25 and fishes 26– 28 use camouflage to avoid being spotted by predators. In the epipelagic marine environment ( i.e. Both pigment dispersion and aggregation in metazoan melanophores are described as microtubule-dependent processes 17– 20. melatonin, melanocortin, prolactin, γ-aminobutyric acid, calcineurin, cyclic adenosine monophosphate, inositol triphosphate, dynein, kinesin, extraocular opsins, melanin) in a large diversity of organisms 6– 16. These processes appeared to be conserved across metazoans with common use of multiple molecular actors ( e.g. Pathways controlling colour modifications involve the motion of pigmented granule ( i.e. Skin colour modifications need to be under fine-tuned modulation to display an efficient camouflage. This mechanism may be passive, with no colour modification during the organism life, or active, with the ability to gradually modify the skin colour to adapt the background colour ( i.e. The cryptic strategy aims to facilitate the concealment of the projected shadow by the body adding a clear betterment to the organism’s survival 5. Countershading, a type of camouflage strategy which consists of the gradation of colour from dark on the dorsal side to light on the ventral area, is generally considered as an efficient hiding strategy spread mainly in the marine environment 1– 4. An efficient camouflage strategy needs two essential and interconnected mechanisms: ( i) an accurate sensory machinery to evaluate the environment and ( ii) the genetic determination for expressing a phenotypic trait mimicking the environment or/and the capability to modulate the skin colouration to match with the background colour. By mimicking the colour of the environment background, many organisms successfully escape predation 1, 2. This suggests a functional link between photoreception and photoemission in the photogenic tissue of lanternsharks and gives precious insights into the bioluminescence control of these organisms.Ĭamouflage is one of the most powerful anti-predatory tools on earth 1. The lanternshark luminescence then appears to be controlled by the balanced bidirectional motion of ILS cell pigments within the photophore. Conversely, our results highlighted the implication of the α-MSH/ACTH pathway, involving kinesin, in the dispersion of the ILS cell pigment. Our results reveal the implication of Es-Opn3, MT, inositol triphosphate (IP 3), intracellular calcium, calcium-dependent calmodulin and dynein in the ILS cell pigment aggregation. Here, we investigated the role of ( i) Es-Opn3 and ( ii) actors involved in both MT and α-MSH/ACTH pathways on the shark bioluminescence and ILS cell pigment motions. Interestingly, the lanternshark photophore comprises a specific iris-like structure (ILS), partially composed of melanophore-like cells, serving as a photophore shutter. The majority of these compounds (MT, α-MSH, ACTH, opsin) are members of the rapid physiological colour change that regulates the pigment motion within chromatophores in metazoans. The extraocular encephalopsin (Es-Opn3) was also hypothesized to act as a luminescence regulator. This shark displays hormonally controlled bioluminescence in which melatonin (MT) and prolactin (PRL) trigger light emission, while α-melanocyte-stimulating hormone (α-MSH) and adrenocorticotropic hormone (ACTH) play an inhibitory role. The velvet belly lanternshark, Etmopterus spinax, uses counterillumination to disappear in the surrounding blue light of its marine environment.
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