Metallothioneins and trace elements in digestive gland, gills, kidney and gonads of Octopus vulgaris

The Modular Architecture of Metallothioneins Facilitates Domain Rearrangements and Contributes to Their Evolvability in Metal-Accumulating Mollusks

Protein domains are independent structural and functional modules that can rearrange to create new proteins. While the evolution of multidomain proteins through the shuffling of different preexisting domains has been well documented, the evolution of domain repeat proteins and the origin of new domains are less understood. Metallothioneins (MTs) provide a good case study considering that they consist of metal-binding domain repeats, some of them with a likely de novo origin. In mollusks, for instance, most MTs are bidomain proteins that arose by lineage-specific rearrangements between six putative domains: α, β1, β2, β3, γ and δ. Some domains have been characterized in bivalves and gastropods, but nothing is known about the MTs and their domains of other Mollusca classes. To fill this gap, we investigated the metal-binding features of NpoMT1 of Nautilus pompilius (Cephalopoda class) and FcaMT1 of Falcidens caudatus (Caudofoveata class). Interestingly, whereas NpoMT1 consists of α and β1 domains and has a prototypical Cd²⁺ preference, FcaMT1 has a singular preference for Zn²⁺ ions and a distinct domain composition, including a new Caudofoveata-specific δ domain. Overall, our results suggest that the modular architecture of MTs has contributed to MT evolution during mollusk diversification, and exemplify how modularity increases MT evolvability.

First evidence of the utility of cephalopods for biomonitoring program in the field: case of Sepia officinalis south west of Mediterranean Sea (Gulf of Gabes, Tunisia)

This study was carried out to determine the concentration of selected heavy metals in common cuttlefish (Sepia officinalis) caught in the south west of Mediterranean Sea (Gulf of Gabes, Tunisia). To reach this objective, cuttlefish samples were collected from each area (Sfax and Djerba) situated along the Gulf of Gabes, and the concentrations of heavy metals (Cu, Zn, Pb, and Cd) were measured in the gills, gonads, digestive glands, and muscles. Sample preparation and quantification of the metals were accomplished via the wet digestion method and atomic absorption spectroscopy. The levels of heavy metals varied significantly among organs and sites. In fact, the population from Sfax (Gargour) shows the highest concentrations of copper, zinc, and lead compared to the population from Djerba. Globally, recorded metal concentrations were within the range or below the levels in similar species from other regions across the world. To our knowledge, this study is the first that interests to the bioaccumulation of metals in this cuttlefish species from the two investigated areas and to the evaluation of their levels in different tissues.

Influence of sexual dimorphism on stable isotopes and trace element concentrations in the greater hooked squid Moroteuthopsis ingens from New Zealand waters

The Chatham Rise, one of the highest offshore-primary production regions in New Zealand waters, hosts a great abundance and diversity of deep-sea cephalopods including the greater hooked squid, Moroteuthopsis ingens. Stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) and trace element concentrations (Ag, As, Cd, Co, Cr, Cu, Fe, Hg, Ni, Pb, Se, V, and Zn) were assessed in female and male specimens of different size classes (89-563 mm mantle length). Values of δ¹³C and δ¹⁵N were overall higher in females and δ¹³C was further influenced by size and sex. Both muscular mantle (the largest fraction of the total body mass) and digestive gland (the known main storage organ for Ag, Cd, Cu and Zn in many cephalopods) tissues were analysed. Higher levels of Cd were observed in males than in females. A positive effect was found between size and Hg concentrations, which could be related to the ontogenetic descent of larger specimens into deeper waters, where they are exposed to higher Hg concentrations, and/or dietary shifts toward Hg-enriched prey with increasing size. This study provides trace element data for this abundant and ecologically important species, and further reveals higher trace element concentrations (especially Hg) in M. ingens from the Chatham Rise, compared to specimens from the sub-Antarctic zone.

Trace Elements, PPARs, and Metabolic Syndrome

Metabolic syndrome (MetS) is a constellation of metabolic derangements, including central obesity, insulin resistance, hypertension, glucose intolerance, and dyslipidemia. The pathogenesis of MetS has been intensively studied, and now many factors are recognized to contribute to the development of MetS. Among these, trace elements influence the structure of proteins, enzymes, and complex carbohydrates, and thus an imbalance in trace elements is an independent risk factor for MetS. The molecular link between trace elements and metabolic homeostasis has been established, and peroxisome proliferator-activated receptors (PPARs) have appeared as key regulators bridging these two elements. This is because on one hand, PPARs are actively involved in various metabolic processes, such as abdominal adiposity and insulin sensitivity, and on the other hand, PPARs sensitively respond to changes in trace elements. For example, an iron overload attenuates hepatic mRNA expression of Ppar-α; zinc supplementation is considered to recover the DNA-binding activity of PPAR-α, which is impaired in steatotic mouse liver; selenium administration downregulates mRNA expression of Ppar-γ, thereby improving lipid metabolism and oxidative status in the liver of high-fat diet (HFD)-fed mice. More importantly, PPARs' expression and activity are under the control of the circadian clock and show a robust 24 h rhythmicity, which might be the reasons for the side effects and the clinical limitations of trace elements targeting PPARs. Taken together, understanding the casual relationships among trace elements, PPARs' actions, and the pathogenesis of MetS is of great importance. Further studies are required to explore the chronopharmacological effects of trace elements on the diurnal oscillation of PPARs and the consequent development of MetS.

Fatty acids and elemental composition as biomarkers of Octopus vulgaris populations: Does origin matter?

The present study describes the novel use of fatty acids (FAs) and element profiles of Octopus vulgaris inhabiting three coastal areas in the W-Mediterranean Sea. These populations are exposed to different anthropogenic activities, and were compared at different geographical scales. The FA composition in the mantle of O. vulgaris exhibited significant differences in 22:6 n-3 (DHA) and 22:5 n-3 (EPA) among the sampled populations. The essential microelements Fe, Cu, Zn and Ni, and the non-essential microelements As, Sr, Al and Cd were the main contributors of variability among sampled octopus populations, with some notable differences among tissues. The variations in the FAs and elemental composition in octopus tissues were detected with other populations throughout the species distribution range, which might reflect differences in natural habitats and foraging strategies. Therefore, these may be considered biomarkers as a proxy to distinguish the origin of octopus specimens at different scales.

The Role of the Cephalopod Digestive Gland in the Storage and Detoxification of Marine Pollutants

The relevance of cephalopods for fisheries and even aquaculture, is raising concerns on the relationship between these molluscs and environmental stressors, from climate change to pollution. However, how these organisms cope with environmental toxicants is far less understood than for other molluscs, especially bivalves, which are frontline models in aquatic toxicology. Although, sharing the same basic body plan, cephalopods hold distinct adaptations, often unique, as they are active predators with high growth and metabolic rates. Most studies on the digestive gland, the analog to the vertebrate liver, focused on metal bioaccumulation and its relation to environmental concentrations, with indication for the involvement of special cellular structures (like spherulae) and proteins. Although the functioning of phase I and II enzymes of detoxification in molluscs is controversial, there is evidence for CYP-mediated bioactivation, albeit with lower activity than vertebrates, but this issue needs yet much research. Through novel molecular tools, toxicology-relevant genes and proteins are being unraveled, from metallothioneins to heat-shock proteins and phase II conjugation enzymes, which highlights the importance of increasing genomic annotation as paramount to understand toxicant-specific pathways. However, little is known on how organic toxicants are stored, metabolized and eliminated, albeit some evidence from biomarker approaches, particularly those related to oxidative stress, suggesting that these molluscs' digestive gland is indeed responsive to chemical aggression. Additionally, cause-effect relationships between pollutants and toxicopathic effects are little understood, thus compromising, if not the deployment of these organisms for biomonitoring, at least understanding how they are affected by anthropogenically-induced global change.

Metal accumulation and oxidative stress biomarkers in octopus (Octopus vulgaris) from Northwest Atlantic

Metals are ubiquitous in the environment and accumulate in aquatic organisms and are known for their ability to enhance the production of reactive oxygen species (ROS). In aquatic species, oxidative stress mechanisms have been studied by measuring antioxidant enzyme activities and oxidative damages in tissues. The aim of this study was to apply and validate a set of oxidative stress biomarkers and correlate responses with metal contents in tissues of common octopus (Octopus vulgaris). Antioxidant enzyme activity (catalase--CAT, superoxide dismutase--SOD and glutathione S-transferases--GST), oxidative damages (lipid peroxidation--LPO and protein carbonyl content--PCO) and metal content (Cu, Zn, Pb, Cd and As) in the digestive gland and arm of octopus, collected in the NW Portuguese coast in different periods, were assessed after capture and after 14 days in captivity. CAT and SOD activities were highly responsive to fluctuations in metal concentrations and able to reduce oxidative damage, LPO and PCO in the digestive gland. CAT activity was also positively correlated with SOD and GST activities, which emphasizes that the three enzymes respond in a coordinated way to metal induced oxidative stress. Our results validate the use of oxidative stress biomarkers to assess metal pollution effects in this ecological and commercial relevant species. Moreover, octopus seems to have the ability to control oxidative damage by triggering an antioxidant enzyme coordinated response in the digestive gland.

Transcriptome analysis of the Octopus vulgaris central nervous system

Background

Cephalopoda are a class of Mollusca species found in all the world's oceans. They are an important model organism in neurobiology. Unfortunately, the lack of neuronal molecular sequences, such as ESTs, transcriptomic or genomic information, has limited the development of molecular neurobiology research in this unique model organism.

Results

With high-throughput Illumina Solexa sequencing technology, we have generated 59,859 high quality sequences from 12,918,391 paired-end reads. Using BLASTx/BLASTn, 12,227 contigs have blast hits in the Swissprot, NR protein database and NT nucleotide database with E-value cutoff 1e⁻⁵. The comparison between the Octopus vulgaris central nervous system (CNS) library and the Aplysia californica/Lymnaea stagnalis CNS ESTs library yielded 5.93%/13.45% of O. vulgaris sequences with significant matches (1e⁻⁵) using BLASTn/tBLASTx. Meanwhile the hit percentage of the recently published Schistocerca gregaria, Tilapia or Hirudo medicinalis CNS library to the O. vulgaris CNS library is 21.03%–46.19%. We constructed the Phylogenetic tree using two genes related to CNS function, Synaptotagmin-7 and Synaptophysin. Lastly, we demonstrated that O. vulgaris may have a vertebrate-like Blood-Brain Barrier based on bioinformatic analysis.

Conclusion

This study provides a mass of molecular information that will contribute to further molecular biology research on O. vulgaris. In our presentation of the first CNS transcriptome analysis of O. vulgaris, we hope to accelerate the study of functional molecular neurobiology and comparative evolutionary biology.