Pigmented Sheath Research Articles

Maintain the light, long-term seasonal monitoring of luminous capabilities in the brittle star Amphiura filiformis

The European brittle star Amphiura filiformis emits blue light, via a Renilla-like luciferase, which depends on the dietary acquisition of coelenterazine. Questions remain regarding luciferin availability across seasons and the persistence of luminous capabilities after a single boost of coelenterazine. To date, no study has explored the seasonal, long-term monitoring of these luminous capabilities or the tracking of luciferase expression in photogenic tissues. Through multidisciplinary analysis, we demonstrate that luminous capabilities evolve according to the exogenous acquisition of coelenterazine throughout adult life. Moreover, no coelenterazine storage forms are detected within the arms tissues. Luciferase expression persists throughout the seasons, and coelenterazine's presence in the brittle star diet is the only limiting factor for the bioluminescent reaction. No seasonal variation is observed, involving a continuous presence of prey containing coelenterazine. The ultrastructure description provides a morphological context to investigate the green autofluorescence signal attributed to coelenterazine during luciferin acquisition. Finally, histological analyses support the hypothesis of a pigmented sheath leading light to the tip of the spine. These insights improve our understanding of the bioluminescence phenomenon in this burrowing brittle star.

Evolutionary Conservation of Photophore Ultrastructure in Sharks: The Case of a Dalatiid Squalomorph

Bioluminescence is a common ecological trait among many marine organisms, including three shark families: Etmopteridae, Dalatiidae, and Somniosidae. The kitefin shark, Dalatias licha (Bonnaterre, 1788), from the Dalatiidae family is the largest known luminous vertebrate. This study compares the light organ ultrastructure of D. licha with that of Etmopterus spinax, the type species of Etmopteridae, to gain a deeper understanding of the light emission process and its evolutionary conservation within shark families. The ultrastructure of D. licha’s photophores and the morphological changes that occur after hormonal stimulation (via melatonin and α-MSH, which stimulate or inhibit the bioluminescence, respectively) were examined. The photophores consist of a spherical pigmented sheath surrounding a unique, regionalized light-emitting cell (photocyte). The photocyte’s basal area contains a specific area filled with granular inclusions that resemble the glowon-type microsources of E. spinax, suggesting that this area is the intracellular site of light emission. An acidophilic secretion, not present in Etmopteridae, is also observed within the granular area and may be involved in photogenesis. The ultrastructure analysis reveals no lens cells or reticular layer, unlike in Etmopteridae photophores, indicating a simpler organization in Dalatiidae photophores. Melatonin stimulation causes the removal of pigments from the photophore-associated melanophores and an increase in the granular inclusion diameter and coverage in the granular area, further showing that this last area is the potential site of light emission, while α-MSH stimulation causes the extension of the melanophore pigments and a decrease in the granular inclusion diameter and coverage. These results support the evolutive conservation of photophore functional organization across luminous etmopterid and dalatiid sharks.

Histological evidence for secretory bioluminescence from pectoral pockets of\xa0the American Pocket Shark (Mollisquama mississippiensis)

The function of pocket shark pectoral pockets has puzzled scientists over decades. Here, we show that the pockets of the American Pocket Shark (Mollisquama mississippiensis) contain a brightly fluorescent stratified cubic epithelium enclosed in a pigmented sheath and in close contact with the basal cartilage of the pectoral fins; cells of this epithelium display a centripetal gradient in size and a centrifuge gradient in fluorescence. These results strongly support the idea that pocket shark’s pockets are exocrine holocrine glands capable of discharging a bioluminescent fluid, potentially upon a given movement of the pectoral fin. Such capability has been reported in many other marine organisms and is typically used as a close-range defensive trick. In situ observations would be required to confirm this hypothesis.

Anatomy and histology of reproductive system of adult male mint leaf beetle Chrysolina herbacea (Duftschmid, 1825) (Coleoptera: Chrysomelidae).

In this study, anatomy and histology of the male reproductive system of Chrysolina herbacea (Duftschmid 1825) (Coleoptera: Chrysomelidae) are described and illustrated by using light and scanning electron microscopies. Data from the male gonad of this species provide more extended and precise knowledge regarding the histoanatomical structure of the reproductive system in Chrysomelidae. The male reproductive system in C. herbacea consists of paired bilobed testes, two paired vas efferentia, paired seminal vesicles, paired vas deferentia, paired tubular accessory glands, a ductus ejaculatorius, and an aedeagus. Each testis consists of 40 follicles enveloped in a yellow pigmented sheath. In the light and scanning electron microscope examinations of male reproductive system of C. herbacea, different spermatogenesis stages (spermatocytes, spermatids, and spermatozoa) are found. Each testes follicle joins with the vas efferens surrounded by monolayered cubic epithelium with oval nuclei. Epithelial cells are covered from the outside with a thin layer of muscle and sheath. Vas efferens connect to vas deferens that may have an enlarged and differentiated region = seminal vesicle. Mature spermatozoa are seen in the lumen of the vas efferens, seminal vesicle, and vas deferens. There is a pair of accessory glands with a convoluted appearance in the tubular structure around the vas deferens. The vas deferens is a straight tube which leads into the proximal end of the ductus ejaculatorius. Ductus ejaculatorius wall is surrounded by intima, monolayer epithelium, and a thick muscle layer with many nuclei. The distal section of the ductus ejaculatorius is housed within the aedeagus.

Ultrastructural organization of lantern shark (Etmopterus spinax Linnaeus, 1758) photophores

Etmopterus spinax Linnaeus, 1758 is a deepsea lantern shark that emits blue light thanks to thousands of tiny cup-shaped organs made of a pigmented sheath enclosing light-emitting cells topped by an iris-like structure and a lens. In this study, we investigate the ultrastructure of these photophores in order to improve our understanding of the light emission process. The presence of a novel layer, a putative reflector upholstering the pigmented sheath, is highlighted. The intracellular organization of the photocytes is addressed. They appear as regionalized cells: their basal area is occupied by an ovoid nucleus, their medial area is highly vesiculated and their apical area, oriented toward the photophore center, displays small granular inclusions. We hypothesize this granular area to be the intracellular site of photogenesis in E. spinax, as it is also the most fluorescent part of the photocyte.

Morphology and control of photogenic structures in a rare dwarf pelagic lantern shark ( Etmopterus splendidus)

The shark genus Etmopterus encompasses numerous deep-sea species that are widely distributed throughout the world's oceans and share the capability to emit light thanks to numerous tiny epidermal photogenic organs called photophores. Despite the potential wide ecological interest of this light emission, it is still a poorly studied aspect of shark biology, mostly due to the challenges inherent to the study of uncommon deep-sea animals. During a collection trip in waters around Okinawa Island, we had the opportunity to collect, maintain and study specimens of Etmopterus splendidus, a small pelagic lantern shark that was not previously known from this area. Analyses show that (i) the photophore density of this species varies according to the different parts of the body, which led to a heterogeneous photogenic pattern; (ii) photophore harbour the classical structure found in other etmopterid sharks, i.e. a cluster of photocytes enclosed in a pigmented sheath and surmounted by pigmented and lens cells; (iii) the physiological control of these photophores appears similar to what was found in the distantly related Etmopterus spinax, i.e. including hormonal and neural inputs as well as the action of pigmented cells overlying the photocytes. These results indicate that E. splendidus luminescence is probably used for more than one purpose, and support the idea that the physiological control of lantern shark photophores was selected early in the evolution of these sharks.

Rainfordia opercularis, a liopropomin serranid (Teleostei: Serranidae: Epinephelinae): corroborative evidence from settlement-stage larvae

Rainfordia opercularis was described in 1923 from a single specimen taken in Edgecumbe Bay, Queensland, Australia. The species is rare in museum collections, and the larvae have not been described. In 1999, two settlement-stage larvae (20–21 mm in standard length) were collected in light traps set off Lizard Island, Great Barrier Reef, Queensland. The smaller of the two has one thin, flexible, extremely elongate dorsal-fin spine encased in a pigmented sheath. The larger specimen lacks an elongate dorsal-fin spine and exhibits caudal-fin pigment characteristic of adults. A combination of features in one or both of the settlement-stage larvae support the placement of Rainfordia in the epinepheline-serranid tribe Liopropomini: presence of an elongate, filamentous dorsal-fin spine serially associated with the first dorsal-fin pterygiophore; presence of a spine on the inner preopercular ridge; presence of dense pigment on the frontals; absence of an elongate spine at the angle of the preopercle; and absence of supraorbital spination.

The Nature of the Pigmented Sheath in Drosophila Tumors

The Nature of the Pigmented Sheath in <i>Drosophila</i> Tumors