Glycosaminoglycans in the skin mucus of rainbow trout (Salmo gairdneri)

Development of a Mucus Gland Bioreactor in Loach Paramisgurnus dabryanus

Most currently available bioreactors have some defects in the expression, activity, or purification of target protein and peptide molecules, whereas the mucus gland of fish can overcome these defects to become a novel bioreactor for the biopharmaceutical industry. In this study, we have evaluated the practicability of developing a mucus gland bioreactor in loach (Paramisgurnus dabryanus). A transgenic construct pT2-krt8-IFN1 was obtained by subcloning the promoter of zebrafish keratin 8 gene and the type I interferon (IFN1) cDNA of grass carp into the SB transposon. The IFN1 expressed in CIK cells exhibited an antiviral activity against the replication of GCRV873 and activated two genes downstream of JAK-STAT signaling pathway. A transgenic loach line was then generated by microinjection of the pT2-krt8-IFN1 plasmids and in vitro synthesized capped SB11 mRNA. Southern blots indicated that a single copy of IFN1 gene was stably integrated into the genome of transgenic loach. The expression of grass carp IFN1 in transgenic loaches was detected with RT-PCR and Western blots. About 0.0825 µg of grass carp IFN1 was detected in 20 µL mucus from transgenic loaches. At a viral titer of 1 × 10³ PFU/mL, plaque numbers on plates containing mucus from transgenic loaches reduced by 18% in comparison with those of the control, indicating that mucus of IFN1-transgenic loaches exhibited an antiviral activity. Thus, we have successfully created a mucus gland bioreactor that has great potential for the production of various proteins and peptides.

Bacteria evoke alarm behaviour in zebrafish

When injured, fish release an alarm substance (Schreckstoff) that elicits fear in members of their shoal. Although Schreckstoff has been proposed to be produced by club cells in the skin, several observations indicate that these giant cells function primarily in immunity. Previous data indicate that the alarm substance can be isolated from mucus. Here we show that mucus, as well as bacteria, are transported from the external surface into club cells, by cytoplasmic transfer or invasion of cells, including neutrophils. The presence of bacteria inside club cells raises the possibility that the alarm substance may contain a bacterial component. Indeed, lysate from a zebrafish Staphylococcus isolate is sufficient to elicit alarm behaviour, acting in concert with a substance from fish. These results suggest that Schreckstoff, which allows one individual to unwittingly change the emotional state of the surrounding population, derives from two kingdoms and is associated with processes that protect the host from bacteria.

Biological and Ecological Roles of External Fish Mucus: A Review

Fish mucus layers are the main surface of exchange between fish and the environment, and they possess important biological and ecological functions. Fish mucus research is increasing rapidly, along with the development of high-throughput techniques, which allow the simultaneous study of numerous genes and molecules, enabling a deeper understanding of the fish mucus composition and its functions. Fish mucus plays a major role against fish infections, and research has mostly focused on the study of fish mucus bioactive molecules (e.g., antimicrobial peptides and immune-related molecules) and associated microbiota due to their potential in aquaculture and human medicine. However, external fish mucus surfaces also play important roles in social relationships between conspecifics (fish shoaling, spawning synchronisation, suitable habitat finding, or alarm signals) and in interspecific interactions such as prey-predator relationships, parasite–host interactions, and symbiosis. This article reviews the biological and ecological roles of external (gills and skin) fish mucus, discussing its importance in fish protection against pathogens and in intra and interspecific interactions. We also discuss the advances that “omics” sciences are bringing into the fish mucus research and their importance in studying the fish mucus composition and functions.

Haemolytic actinoporins interact with carbohydrates using their lipid-binding module

Pore-forming toxins (PFTs) are proteins endowed with metamorphic properties that enable them to stably fold in water solutions as well as in cellular membranes. PFTs produce lytic pores on the plasma membranes of target cells conducive to lesions, playing key roles in the defensive and offensive molecular systems of living organisms. Actinoporins are a family of potent haemolytic toxins produced by sea anemones vigorously studied as a paradigm of α-helical PFTs, in the context of lipid-protein interactions, and in connection with nanopore technologies. We have recently reported that fragaceatoxin C (FraC), an actinoporin, engages biological membranes with a large adhesive motif allowing the simultaneous attachment of up to four lipid molecules prior to pore formation. Since actinoporins also interact with carbohydrates, we sought to understand the molecular and energetic basis of glycan recognition by FraC. By employing structural and biophysical methodologies, we show that FraC engages glycans with low affinity using its lipid-binding module. Contrary to other PFTs requiring separate domains for glycan and lipid recognition, the small single-domain actinoporins economize resources by achieving dual recognition with a single binding module. This mechanism could enhance the recruitment of actinoporins to the surface of target tissues in their marine environment.This article is part of the themed issue 'Membrane pores: from structure and assembly, to medicine and technology'.

Skin Mucus of Gilthead Sea Bream (Sparus aurata L.). Protein Mapping and Regulation in Chronically Stressed Fish

The skin mucus of gilthead sea bream was mapped by one-dimensional gel electrophoresis followed by liquid chromatography coupled to high resolution mass spectrometry using a quadrupole time-of-flight mass analyzer. More than 2,000 proteins were identified with a protein score filter of 30. The identified proteins were represented in 418 canonical pathways of the Ingenuity Pathway software. After filtering by canonical pathway overlapping, the retained proteins were clustered in three groups. The mitochondrial cluster contained 59 proteins related to oxidative phosphorylation and mitochondrial dysfunction. The second cluster contained 79 proteins related to antigen presentation and protein ubiquitination pathways. The third cluster contained 257 proteins where proteins related to protein synthesis, cellular assembly, and epithelial integrity were over-represented. The latter group also included acute phase response signaling. In parallel, two-dimensional gel electrophoresis methodology identified six proteins spots of different protein abundance when comparing unstressed fish with chronically stressed fish in an experimental model that mimicked daily farming activities. The major changes were associated with a higher abundance of cytokeratin 8 in the skin mucus proteome of stressed fish, which was confirmed by immunoblotting. Thus, the increased abundance of markers of skin epithelial turnover results in a promising indicator of chronic stress in fish.

Antioxidant system efficiently protects goldfish gills from Ni(2+)-induced oxidative stress

Fish gills are target organs for waterborne metal ions and this work aimed to investigate the effects of waterborne Ni(2+) (10, 25 and 50 mg L(-1)) on goldfish gills. A special focus was on the relationship between Ni uptake and the homeostasis of reactive oxygen species (ROS) in the gills, the tissue, in direct contact with the metal pollutant. Ni-accumulation in the gills occurred as a function of exposure concentration (R(2)=0.98). The main indices of oxidative stress, namely carbonyl proteins (CP) and lipid peroxides (LOOH), decreased by 21-33% and 21-24%, as well as the activities of principal antioxidant enzymes superoxide dismutase and glutathione-dependent peroxidase, by 29-47% and 41-46%, respectively, in gills of Ni-exposed fish. One of the main players in the antioxidant defense of gills seems to be catalase, which increased by 23-53% in Ni-treated fish, and low molecular mass thiol-containing compounds (L-SH), exceeding untreated controls by 73-105% after fish exposure to 10-50 mg L(-1) of Ni(2+). The increased level of L-SH, mainly represented by reduced glutathione, was supported by enhanced activities of glutathione reductase (by 27-38%), glutathione-S-transferase (56-141%) and glucose-6-phosphate dehydrogenase (by 96-117%) and demonstrates the ability of the antioxidant system of gills to resist Ni-induced oxidative stress.

Crustacean peptide and peptide-like pheromones and kairomones

Crustacean peptide pheromones, kairomones, and substituted amino sugar kairomones are reviewed from a historical perspective. These crustacean information molecules are secondary functions of structural polymers. They are partial hydrolysis products, generated usually by the action of trypsin-like enzymes on proteins, and glycosidase enzymes on glycoproteins and proteoglycans. Structure-function studies based upon synthetic mimics of peptide information molecules show neutral amino acids with a basic carboxyl terminal are active in modifying physiological and or behavioral responses. Behaviorally active substituted amino sugar mimics are disaccharide hydrolysis products of heparin and chondroitin sulfate. Similar molecules are also used as information molecules by a variety of other marine organisms indicating they are a common biological theme.

Metallothionein response in gills of Oreochromis mossambicus exposed to copper in fresh water

Freshwater Oreochromis mossambicus (tilapia) were exposed to 3.2 micromol/l Cu(NO(3))(2) in the water for up to 80 days, and copper (Cu) and immunoreactive metallothionein (irMT) were localized in the branchial epithelium. Cu was demonstrated in mucous cells (MC), chloride cells (CC), pavement cells (PC), respiratory cells (RC), and basal layer cells (BLC) via autometallography combined with alcian blue staining for MC and Na(+)-K(+)-ATPase immunostaining for CC and, on the basis of their location in the epithelium of PC, RC, and BLC. In control fish (water with Cu concentration </=90 nmol/l) incidentally irMT was observed in the area where progenitor cells of the branchial epithelia reside, as demonstrated by proliferating cell nuclear antigen staining. This was also the area where the first increase irMT expression of the Cu exposure was observed. After 2 days of exposure to Cu, irMT was found in CC and PC. From 5 days on, a pronounced irMT staining was observed in BLC of branchial epithelium, which then appeared to migrate and differentiate into mature CC, PC, and RC. We conclude that MT expression in mature CC, PC, and RC requires exposure to Cu in a earlier stage of development of these cells. Once expression is initiated in undifferentiated cells, MT remains expressed throughout the life cycle of the cell.