Luminescence control of Stomiidae photophores

Catecholamine Involvement in the Bioluminescence Control of Two Species of Anthozoans

Bioluminescence, the ability of living organisms to emit visible light, is an important ecological feature for many marine species. To fulfil the ecological role (defence, offence, or communication), bioluminescence needs to be finely controlled. While many benthic anthozoans are luminous, the physiological control of light emission has only been investigated in the sea pansy, Renilla koellikeri. Through pharmacological investigations, a nervous catecholaminergic bioluminescence control was demonstrated for the common sea pen, Pennatula phosphorea, and the tall sea pen, Funiculina quadrangularis. Results highlight the involvement of adrenaline as the main neuroeffector triggering clusters of luminescent flashes. While noradrenaline and octopamine elicit flashes in P. phosphorea, these two biogenic amines do not trigger significant light production in F. quadrangularis. All these neurotransmitters act on both the endodermal photocytes located at the base and crown of autozooids and specific chambers of water-pumping siphonozooids. Combined with previous data on R. koellikeri, our results suggest that a catecholaminergic control mechanisms of bioluminescence may be conserved in Anthozoans.

Photophore Morphogenesis and Extraocular Encephalopsin Expression during the Embryogenesis of Smalleye Pygmy Shark (Squaliolus aliae)

Bioluminescence is a common phenomenon in marine organisms, especially in deep water where faint blue light remains. Among elasmobranchs, three families display the ability to emit light, the Etmopteridae, the Dalatiidae, and the Somniosidae. Luminous sharks have thousands of minute light organs, called photophores, that are mainly present ventrally and produce light. The main function of shark luminescence is counterillumination to camouflage the shark silhouette by mimicking the residual ambient light and avoiding being spotted by predators underneath. To perform counterillumination efficiently, luminescence needs to be finely adjusted. A new type of control was recently demonstrated via extraocular photoreception at the level of the light organ. An encephalopsin (i.e., opsin 3) was shown to be expressed in the vicinity of the photophore of an Etmopteridae species, Etmopterus spinax. This opsin was also demonstrated to be expressed concomitantly with the photophore development (i.e., when photophores become able to produce light) during E. spinax embryogenesis. To understand the photophore morphogenesis of different shark families, we analyzed the smalleye pygmy shark, Squaliolus aliae, with a photophore formation which represents the first report on the Dalatiidae family. Since Dalatiidae and Etmopteridae are phylogenetically closely related, the photophore morphogenesis was compared with an Etmopteridae representative, Etmopterus spinax. The results also reveal that Squaliolus aliae shares similar encephalopsin expression pattern as in Etmopterus spinax, which further supports evolutionary conservation of photophore morphogenesis as well as its own encephalopsin-based light perception across the two luminous shark families.

Terrestrial and marine bioluminescent organisms from the Indian subcontinent: a review

The inception of bioluminescence by Harvey (1952) has led to a Nobel Prize to Osamu Shimomura (Chemistry, 2008) in biological research. Consequently, in recent years, bioluminescence-based assays to monitor toxic pollutants as a real-time marker, to study various diseases and their propagation in plants and animals, are developed in many countries. The emission ability of bioluminescence is improved by gene modification, and also, search for novel bioluminescent systems is underway. Over 100 species of organisms belonging to different taxa are known to be luminous in India. However, the diversity and distribution of luminous organisms and their applications are studied scarcely in the Indian scenario. In this context, the present review provides an overview of the current understanding of various bioluminescent organisms, functions, and applications. A detailed checklist of known bioluminescent organisms from India's marine, terrestrial, and freshwater ecosystems is detailed. This review infers that Indian scientists are needed to extend their research on various aspects of luminescent organisms such as biodiversity, genomics, and chemical mechanisms for conservation, ecological, and biomedical applications.

Bioluminescence in lanternsharks: Insight from hormone receptor localization

As part of the study of their bioluminescence, the deep-sea lanternshark Etmopterus spinax and Etmopterus molleri (Chondrichthyes, Etmopteridae) received growing interest over the past ten years. These mesopelagic sharks produce light thanks to a finely tuned hormonal control involving melatonin, adrenocorticotropic hormone and α-melanocyte-stimulating hormone. Receptors of these hormones, respectively the melatonin receptors and the melanocortin receptors, are all members of the G-protein coupled receptor family i.e. coupled with specific G proteins involved in the preliminary steps of their transduction pathways. The present study highlights the specific localization of the hormonal receptors, as well as of their associated G-proteins within the light organs, the so-called photophores, in E. spinax and E. molleri through immunohistofluorescence technic. Our results allow gaining insight into the molecular actors and mechanisms involved in the control of the light emission in Etmopterid sharks.

The first evidence of intrinsic epidermal bioluminescence within ray-finned fishes in the linebelly swallower Pseudoscopelus sagamianus (Chiasmodontidae)

External and histological examination of the photophores of the linebelly swallower Pseudoscopelus sagamianus reveal three epidermal layers of cells that form the light-producing and light-transmitting components of the photophores. Photophores among the examined photophore tracts are not significantly different in structure but the presence of mucous cells in the superficial layers of the photophore suggest continued function of the epidermal photophore in contributing to the mucous coat. This is the first evidence of intrinsic bioluminescence in primarily epidermal photophores reported in ray-finned fishes.

Adrenocorticotropic Hormone and Cyclic Adenosine Monophosphate are Involved in the Control of Shark Bioluminescence

Among Etmopteridae and Dalatiidae, luminous species use hormonal control to regulate bioluminescence. Melatonin (MT) triggers light emission and, conversely, alpha melanocyte-stimulating hormone (α-MSH) actively reduces ongoing luminescence. Prolactin (PRL) acts differentially, triggering light emission in Etmopteridae and inhibiting it in Dalatiidae. Interestingly, these hormones are also known as regulators of skin pigment movements in vertebrates. One other hormone, the adrenocorticotropic hormone (ACTH), also members of the skin pigmentation regulators, is here pharmacologically tested on the light emission. Results show that ACTH inhibits luminescence in both families. Moreover, as MT and α-MSH/ACTH receptors are members of the G-protein coupled receptor (GPCR) family, we investigated the effect of hormonal treatments on the cAMP level of photophores through specific cAMP assays. Our results highlight the involvement of ACTH and cAMP in the control of light emission in sharks and suggest a functional similarity between skin pigment migration and luminescence control, this latter being mediated by pigment movements in the light organ-associated iris-like structure cells.

Etmopterus spinax, the velvet belly lanternshark, does not use bacterial luminescence

Marine organisms are able to produce light using either their own luminous system, called intrinsic bioluminescence, or symbiotic luminous bacteria, called extrinsic bioluminescence. Among bioluminescent vertebrates, Osteichthyes are known to harbor both types of bioluminescence, while no study has so far addressed the potential use of intrinsic/extrinsic luminescence in elasmobranchs. In sharks, two families are known to emit light: Etmopteridae and Dalatiidae. The deep-sea bioluminescent Etmopteridae, Etmopterus spinax, has received a particular interest over the past fifteen years and its bioluminescence control was investigated in depth. However, the nature of the shark luminous system still remains enigmatic. The present work was undertaken to assess whether the light of this shark species originates from a bioluminescent bacterial symbiosis. Using fluorescent in situ hybridization (FISH) and transmission electron microscopy (TEM) image analyses, this study supports the conclusion that the bioluminescence in the deep-sea lanternshark, Etmopterus spinax, is not of bacterial origin.