14-3-3 proteins are luciferases candidate proteins from lanternfish Diaphus watasei.

The lanternfish is a deep-sea fish with ventral-lateral and head photophores. It uses its ventral-lateral photophores to camouflage its ventral silhouette, a strategy called counterillumination. The bioluminescent reaction of lanternfish involves coelenterazine as a substrate luciferin but the enzyme catalyzing the bioluminescent reaction has not been identified. We report a candidate enzyme of luciferase from lanternfish Diaphus watasei. We purified the luciferase and performed SDS-PAGE analysis resulted in two bands corresponding to the activity, and following mass spectrometry analysis detected three 14-3-3 proteins of which functions is known to exhibit protein-protein interactions. The molecular weights and isoelectric points of the 14-3-3 proteins were almost consistent with the luciferase properties. The addition of two 14-3-3 binding compounds, R18 peptide and fusicoccin, resulted in the inhibition of the luciferase activity. However, the two 14-3-3 recombinant proteins showed very slight luminescence activity. These results suggested that the 14-3-3 proteins are candidate luciferases of D. watasei.

Etmopterus lantern sharks use coelenterazine as the substrate for their luciferin-luciferase bioluminescence system.

The lantern shark genus Etmopterus contains approximately 40 species of deep-sea bioluminescent cartilaginous fishes. They emit blue light mainly from the ventral body surface. The biological functions of this bioluminescence have been discussed based on the luminescence patterns, but the bioluminescence mechanism remains uncertain. In this study, we detected both coelenterazine and coelenterazine-dependent luciferase activity in the ventral photophore tissue of Etmopterus molleri. The results suggested that bioluminescence in lantern sharks is produced using coelenterazine as the substrate for the luciferin-luciferase reaction, as some luminous bony fishes.

Reflector of the body photophore in lanternfish is mechanistically tuned to project the biochemical emission in photocytes for counterillumination.

Lanternfish, a family Myctophidae, use ventro-lateral body photophores for camouflage of the ventral silhouette, a strategy called counterillumination. While other deep-sea fishes possess pigmented filters and silver reflectors to match sunlight filtering down through the depths, myctophids developed a blue-green reflector for this purpose. In this study, we showed in a lanternfish Diaphus watasei that the reflector comprised monolayered iridophores containing multilayered guanine crystals which enable high reflection with light interference colouration. Platelets shape in body photophores is an unique near-regular hexagonal, probably to allow the homogeneity of reflection angle of the luminescence from photocytes. Focus point of the parabola-like reflector is positioned on the photocytes that ensures the light produced from the photocytes is redirected to the ventral direction. In vitro luminescence reaction using purified luciferase and the substrate coelenterazine showed the light emission at λmax 454 nm, while reflection spectra of the iridophores exhibit peaks at longer wavelength, which accomplish to alter the luminescence emitted from photocytes to longer wavelength to fit the mesopelagic light environment. Taken together, we revealed multiple mechanistic elaborations in myctophid body photophores to achieve effective control of biochemical luminescence for counterillumination.

Occurrence of bioluminescent and nonbioluminescent species in the littoral earthworm genus Pontodrilus.

Pontodrilus litoralis is a cosmopolitan littoral earthworm known to exhibit bioluminescence. Recently, a congeneric species, Pontodrilus longissimus, from Thailand was described. These species are sympatric, but their burrowing depths on Thai beaches are different. In this study, we examined the in vivo and in vitro bioluminescent properties of P. longissimus and P. litoralis. Mechanical stimulation induced in vivo luminescence in P. litoralis, as reported previously, but not in P. longissimus. In vitro cross-reaction tests between these species revealed the absence of luciferin and luciferase activities in P. longissimus. The coelomic fluid of P. litoralis had strong fluorescence that matched the spectral maximum of its bioluminescence, but the same result was not observed for P. longissimus. These results suggest that P. litoralis has luminescence abilities due to the creation of bioluminescent components (i.e., luciferin, luciferase, and light emitters). The presence of both luminous and nonluminous species in a single genus is likely widespread, but only a few examples have been confirmed. Our findings provide insight into the possible functions of bioluminescence in earthworms, such as avoiding predation by littoral earwigs.

Arginine vasotocin reduces levels of cooperative behaviour in a cleaner fish.

Cooperation between unrelated individuals usually involves investments that often mean a decrease in immediate payoffs, but ensure future benefits. Here we investigated the potential role of the neuropeptides Arginine-vasotocin (AVT) and Isotocin (IT) as proximate agents affecting individuals' cooperative levels in the Indo-pacific bluestreak cleaner wrasse Labroides dimidiatus. Their 'client' reef fish partners only benefit from interacting if cleaners eat ectoparasites and refrain from gleaning preferred client mucus. Thus, cleaners must control their impulse to eat according to their preference, and eat less preferred items to maintain ongoing interactions and avoid clients' leaving or punishing. We found that solely the experimental transient higher dosage of AVT led to a decrease of cleaners' willingness to feed against their preference, while IT and AVT antagonists had no significant effects. The sole effect of AVT on cleaner's performance may imply a link between AVT's influence and a potential activation of a stress response. Our results confirm the importance of the AVT/AVP system as an agent affecting levels of cooperation, offering a potential mechanistic pathway for the reported flexible service quality that cleaners provide their clients.