Ultrastructure and glycoconjugate pattern of the foot epithelium of the abalone Haliotis tuberculata (Linnaeus, 1758) (Gastropoda, Haliotidae)

Histological, elemental, and ultrastructural analysis of melanin in mantle of Pacific oyster (Crassostrea gigas)

Colorful shell of bivalve is mainly because of the biological pigments, of which melanin plays an important role in shell color formation. More and more studies focus on the genes function involved in melanin synthesis, but relatively few studies address the biochemical character and ultrastructure of melanin in bivalve from microscopic perspective. Here, we investigated the histological structure of mantle of Crassostrea gigas with orange shell color. Distribution of melanin in mantle was verified with histochemical staining. In addition, immunofluorescence technique showed that strongly positive signal of CgTYR was specific to the mantle margin, which is consistence with the location of brown granules in H&E staining. The further result of elementary composition of melanin displayed that metal Ca, Fe, and Zn were detected using scanning transmission electron microscope and energy dispersive spectroscopy mapping methods. Next, based on TEM observations, it was speculated that the series of cellular events leading to the formation and release of melanin. Melanocyte in the primary stage showed many mitochondria and rough endoplasmic reticulum as well as an extensive Golgi complex with numerous vesicles intermingled with melanosome. Subsequently, melanosome was expended and their hue gradually intensified, and Golgi complex and mitochondria were still observed in the cytoplasm. Finally, after melanosome was discharged into intercellular spaces, the disintegration of membranes in some cells, and severe cellular vacuolization. These data enrich the understanding of ultrastructural characteristic and formation of melanin in mantle of bivalve and pave the way for further investigating shell coloration at the cellular level.

Molecular Mechanisms of Spawning Habits for the Adaptive Radiation of Endemic East Asian Cyprinid Fishes

Despite the widespread recognition of adaptive radiation as a driver of speciation, the mechanisms by which natural selection generates new species are incompletely understood. The evolutionary radiation of endemic East Asian cyprinids has been proposed as evolving through a change in spawning habits, involving a transition from semibuoyant eggs to adhesive eggs in response to crosslinked river-lake system formation. Here, we investigated the molecular mechanisms that underpin this radiation, associated with egg hydration and adhesiveness. We demonstrated that semibuoyant eggs enhance hydration by increasing the degradation of yolk protein and accumulation of Ca2+ and Mg2+ ions, while adhesive eggs improve adhesiveness and hardness of the egg envelope by producing an adhesive layer and a unique 4th layer to the egg envelope. Based on multiomics analyses and verification tests, we showed that during the process of adaptive radiation, adhesive eggs downregulated the "vitellogenin degradation pathway," "zinc metalloprotease pathway," and "ubiquitin-proteasome pathway" and the pathways of Ca2+ and Mg2+ active transport to reduce their hydration. At the same time, adhesive eggs upregulated the crosslinks of microfilament-associated proteins and adhesive-related proteins, the hardening-related proteins of the egg envelope, and the biosynthesis of glycosaminoglycan in the ovary to generate adhesiveness. These findings illustrate the novel molecular mechanisms associated with hydration and adhesiveness of freshwater fish eggs and identify critical molecular mechanisms involved in the adaptive radiation of endemic East Asian cyprinids. We propose that these key egg attributes may function as "magic traits" in this adaptive radiation.

Changes in marine turbot (Scophthalmus maximus) epidermis and skin mucus composition during development from bilateral larvae to juvenile flat fish

Alike other flat fish, marine turbot has the particularity that changes from larvae with bilateral symmetry to adult with asymmetry, in terms of the position of the eyes. As expected, the skin configuration of this species is also affected by the development and transformation suffered by fish during metamorphosis. In this context, changes in the epidermis of marine turbot were studied using conventional staining and histochemical techniques using six lectins (UEA-I, PNA, RCA-I, WGA, Con A and SBA). During development from larvae to juvenile (3-300 days post-hatching), the epidermis increased in both thickness and the number of cell layers. In fact, the simple cuboidal epithelium observed in larvae at day 3 already became stratified at days 10-12, which sequentially increase in thickness with fish development. Turbot epidermis is composed basically of four cell types: epithelial and mucous or secretory cells that are present through the development, and pigmented cells and a type that the authors described as club-like cells that appear during and post-metamorphosis. The Alcian blue-periodic acid Schiff (AB-PAS) histochemical method revealed the presence of neutral glycoconjugates in mucous and club-like cells at post-metamorphic stages of fish. Accordingly, lectin analysis showed mucous cells containing glycoproteins rich in fucose (UEA-I labelling) and glycoconjugates rich in the sequence galactose-N-acetyl galactosamine (PNA and RCA-I labelling) when this cell type appears. Interestingly, melanophores were observed in the dorsal epidermis of post-metamorphic juveniles. This type of cell contains a black-to-brown pigment that provides the skin the typical colour of this fish species. Changes in mucous coat composition were observed during fish development, which was attributed to different roles of the glycoconjugates.

A Mechanics Study on the Self-Righting of Abalone from the Substrate

In this study, we aim to probe the self-righting behavior of abalone on a substrate based on experiments and mechanistic analyses. A successful self-righting process of abalone is observed, and its critical condition in theory can be given in terms of the rotation angle. Then, according to the moment balance and potential energy minimization, the required tension force of the abalone foot for self-righting is derived with respect to the rotation angle. The experimental result also shows that in many cases the abalone cannot finish this self-righting process. Then, measurements on the tolerant strength of abalone muscle and tolerant adhesion strength of the foot on substrate are both conducted. It is judged that the abalone muscle is strong enough, which can provide enough tension force, and thus, the self-righting mainly depends on the adhesion area of the foot on substrate. These findings cast new light on engineering new types of biomaterials and devices, such as marine equipment and soft robotics.

Impairment of swimming performance in Tritia reticulata (L.) veligers under projected ocean acidification and warming scenarios

Tritia reticulata (L.) is a neogastropod ubiquitous in the coastal communities of the NE Atlantic. Its life cycle relies on the swimming performance of planktonic early life stages, whose sensitivity to the climate conditions projected for the near future, namely of ocean acidification (OA) and warming (W), is, to our best knowledge, unknown. To examine the resilience of larval stages to future environmental conditions, this work investigates the effect of OA-W on the swimming performance of T. reticulata veligers under a range of experimental conditions, based on the end-of-century projections of the Intergovernmental Panel on Climate Change. Veligers were exposed to six experimental scenarios for 14 days, employing a full factorial design with three temperatures (T°C: 18, 20 and 22 °C) and two pH levels (pH_target: 8.1 and 7.8). Mortality was assessed throughout the trial, after which swimming behaviour - characterised by the activity, speed and the distance travelled by veligers - was analysed by automated video recordings in a Zebrabox® device. Mortality increased with OA-W and, although more active, larvae travelled shorter distances revealing reduced swimming speed under acidic and warmer conditions, with the interaction of the tested stressors - pH and T°C - being highly significant. Results motivated the morpho-histological analysis of larvae preserved at the end of the trial, to check for the integrity of the organs involved in veligers' motion: statocysts, velum and foot. Statocyst and velar morpho-structure were conserved but histological damage of metapodial epithelia was evident under acidity, namely an apparent hypertrophy and protrusion of the secretory cells, with dispersed pigmented granules and, at 22 °C, less cilia, with potential functional implications. Negative consequences of the OA-W scenarios tested on veligers' competence are unveiled, pointing towards the eminent threat these phenomena constitute to T. reticulata perpetuation in case no mitigation measures are taken, and projections become effective.

Sialic acid and biology of life: An introduction

Sialic acids are important molecule with high structural diversity. They are known to occur in higher animals such as Echinoderms, Hemichordata, Cephalochorda, and Vertebrata and also in other animals such as Platyhelminthes, Cephalopoda, and Crustaceae. Plants are known to lack sialic acid. But they are reported to occur in viruses, bacteria, protozoa, and fungi. Deaminated neuraminic acid although occurs in vertebrates and bacteria, is reported to occur in abundance in the lower vertebrates. Sialic acids are mostly located in terminal ends of glycoproteins and glycolipids, capsular and tissue polysialic acids, bacterial lipooligosaccharides/polysaccharides, and in different forms that dictate their role in biology. Sialic acid play important roles in human physiology of cell-cell interaction, communication, cell-cell signaling, carbohydrate-protein interactions, cellular aggregation, development processes, immune reactions, reproduction, and in neurobiology and human diseases in enabling the infection process by bacteria and virus, tumor growth and metastasis, microbiome biology, and pathology. It enables molecular mimicry in pathogens that allows them to escape host immune responses. Recently sialic acid has found role in therapeutics. In this chapter we have highlighted the (i) diversity of sialic acid, (ii) their occurrence in the diverse life forms, (iii) sialylation and disease, and (iv) sialic acid and therapeutics.

The mechanics of abalone crawling on sharp objects without injury

Despite the soft appearance of their feet, abalones can crawl quickly on sharp objects. Tests using rough substrates aligned with blades or posts found that the animal has two adaptations to guarantee its safety on these surfaces. Mechanical compression tests showed that the abalone foot muscle is inherently robust and can resist penetration by sharp objects. A finite element simulation indicated that to avoid being pierced, abalone controls the shape of its foot to wrap it around sharp objects, thereby greatly reducing the stress concentration. These analyses may aid the engineering of new materials and devices for fields including soft robotics and aircraft.

Involvement of sulfated biopolymers in adhesive secretions produced by marine invertebrates

Many marine invertebrates use adhesive secretions to attach to underwater surfaces and functional groups borne by their adhesive proteins and carbohydrates, such as catechols and phosphates, play a key role in adhesion. The occurrence of sulfates as recurrent moieties in marine bioadhesives suggests that they could also be involved. However, in most cases, their presence in the adhesive material remains speculative. We investigated the presence of sulfated biopolymers in five marine invertebrates representative of the four types of adhesion encountered in the sea: mussels and tubeworms for permanent adhesion, limpets for transitory adhesion, sea stars for temporary adhesion and sea cucumbers for instantaneous adhesion. The dry adhesive material of mussels, sea stars and sea cucumbers contained about 1% of sulfate. Using anti-sulfotyrosine antibodies and Alcian Blue staining, sulfated proteins and sulfated proteoglycans and/or polysaccharides were identified in the secretory cells and adhesive secretions of all species except the tubeworm. Sulfated proteoglycans appear to play a role only in the non-permanent adhesion of sea stars and limpets in which they could mediate cohesion within the adhesive material. In mussels and sea cucumbers, sulfated biopolymers would rather have an anti-adhesive function, precluding self-adhesion.

Study of surface carbohydrates in Galba truncatula tissues before and after infection with Fasciola hepatica

The presence and distribution of surface carbohydrates in the tissues of Galba truncatula snails uninfected or after infection with Fasciola hepatica as well as on the surface of the snail-pathogenic larval stages of the parasite were studied by lectin labelling assay. This is an attempt to find similarities that indicate possible mimicry, utilised by the parasite as an evasion strategy in this snail-trematode system. Different binding patterns were identified on head-foot-mantle, hepatopancreas, genital glands, renopericardial complex of the host as well as of the snail-pathogenic larval stages of F. hepatica. The infection with F. hepatica leads to changes of labelling with Glycine max in the head-mantle cells and Arachis hypogaea in the tubular epithelium of the hepatopancreas. The lectin binding on the other snail tissues is not changed by the development of the larvae. Our data clearly demonstrated the similarity in labelling of G. truncatula tissues and the surface of the snail-pathogenic larval stages of F. hepatica. The role of glycosylation of the contact surfaces of both organisms in relation to the host-parasite interactions is also discussed.

Unveiling the morphology of the acetabulum in octopus suckers and its role in attachment

In recent years, the attachment mechanism of the octopus sucker has attracted the interest of scientists from different research areas, including biology, engineering, medicine and robotics. From a technological perspective, the main goal is to identify the underlying mechanisms involved in sucker attachment for use in the development of new generations of artificial devices and materials. Recently, the understanding of the morphology of the sucker has been significantly improved; however, the mechanisms that allow attachment remain largely unknown. In this work, we present new anatomical findings: specifically, a protuberance in the acetabular roof in five different octopus species; previously, this protuberance was identified by the authors in Octopus vulgaris. Moreover, we discuss the role of the protuberance and other anatomical structures in attachment with minimal energy consumption.

Food deprivation causes rapid changes in the abundance and glucidic composition of the cutaneous mucous cells of Atlantic salmon Salmo salar L

Cutaneous mucus is the first physical and chemical barrier of fish. This slime layer is secreted by mucous cells located in the epidermis and is mainly composed of glycoproteins that have their origin in the diet. Therefore, food deprivation can potentially change the abundance and glucidic nature of skin mucous cells, thus changing the mucus properties. To test this hypothesis, we conducted an experiment with Atlantic salmon, Salmo salar L. Changes in the number and glucidic nature of epidermal mucus cells were analysed using standard techniques. The outcome of this study shows that food deprivation caused a rapid decrease in the density of epidermal mucous cells in Atlantic salmon. Lectin histochemistry revealed a change in the presence and stainability of some sugar residues in the mucous cells of unfed fish compared with fed fish. Given that the primary reason for mucus secretion in fish is for protection against infections, we speculate that the changes in the mucus properties caused by nutritional stress may affect their disease resistance. This fact is particularly important for fish that spend a period of time deprived of food, either as a part of their natural life cycle, or as part of farming practices.

Hairy suckers: the surface microstructure and its possible functional significance in the Octopus vulgaris sucker

Octopus suckers are able to attach to any smooth surface and many rough surfaces. Here, we have discovered that the sucker surface, which has been hypothesised to be responsible for sealing the orifice during adhesion, is not smooth as previously assumed, but is completely covered by a dense network of hair-like micro-outgrowths. This finding is particularly important because it provides another demonstration of the role of hair-structures in a sealing mechanism in water, similar to that previously described for clingfish and abalones. Moreover, the discovered hairs may provide an additional adhesive mechanism that works in concert with suction. The discovered surface structures might be potentially interesting for biomimetics of novel technical suction cups with improved adhesion capabilities on non-smooth surfaces.

Ultrastructure of plant leaf cuticles in relation to sample preparation as observed by transmission electron microscopy

The leaf cuticular ultrastructure of some plant species has been examined by transmission electron microscopy (TEM) in only few studies. Attending to the different cuticle layers and inner structure, plant cuticles have been grouped into six general morphological types. With the aim of critically examining the effect of cuticle isolation and preparation for TEM analysis on cuticular ultrastructure, adaxial leaf cuticles of blue-gum eucalypt, grey poplar, and European pear were assessed, following a membrane science approach. The embedding and staining protocols affected the ultrastructure of the cuticles analysed. The solubility parameter, surface tension, and contact angles with water of pure Spurr's and LR-White resins were within a similar range. Differences were however estimated for resin : solvent mixtures, since Spurr's resin is combined with acetone and LR-White resin is mixed with ethanol. Given the composite hydrophilic and lipophilic nature of plant cuticles, the particular TEM tissue embedding and staining procedures employed may affect sample ultrastructure and the interpretation of the results in physicochemical and biological terms. It is concluded that tissue preparation procedures may be optimised to facilitate the observation of the micro- and nanostructure of cuticular layers and components with different degrees of polarity and hydrophobicity.