Biotic and environmental stress induces nitration and changes in structure and function of the sea urchin major yolk protein toposome

The Evolution of Nitric Oxide Function: From Reactivity in the Prebiotic Earth to Examples of Biological Roles and Therapeutic Applications

Nitric oxide was once considered to be of marginal interest to the biological sciences and medicine; however, there is now wide recognition, but not yet a comprehensive understanding, of its functions and effects. NO is a reactive, toxic free radical with numerous biological targets, especially metal ions. However, NO and its reaction products also play key roles as reductant and oxidant in biological redox processes, in signal transduction, immunity and infection, as well as other roles. Consequently, it can be sensed, metabolized and modified in biological systems. Here, we present a brief overview of the chemistry and biology of NO—in particular, its origins in geological time and in contemporary biology, its toxic consequences and its critical biological functions. Given that NO, with its intrinsic reactivity, appeared in the early Earth’s atmosphere before the evolution of complex lifeforms, we speculate that the potential for toxicity preceded biological function. To examine this hypothesis, we consider the nature of non-biological and biological targets of NO, the evolution of biological mechanisms for NO detoxification, and how living organisms generate this multifunctional gas.

Protease and DNase Activities of a Very Stable High-Molecular-Mass Multiprotein Complex from Sea Cucumber Eupentacta fraudatrix

Only some human organs, including the liver, are capable of very weak self-regeneration. Some marine echinoderms are very useful for studying the self-regeneration processes of organs and tissues. For example, sea cucumbers Eupentacta fraudatrix (holothurians) demonstrate complete restoration of all organs and the body within several weeks after their division into two parts. Therefore, these cucumbers are a prospective model for studying the general mechanisms of self-regeneration. However, there is no data available yet concerning biomolecules of holothurians, which can stimulate the processes of organ and whole-body regeneration. Investigation of these restoration mechanisms is very important for modern medicine and biology because it can help to understand which hormones, nucleic acids, proteins, enzymes, or complexes play an essential role in self-regeneration. It is possible that stable, polyfunctional, high-molecular-weight protein complexes play an essential role in these processes. It has recently been shown that sea cucumbers Eupentacta fraudatrix contain a very stable multiprotein complex of about 2000 kDa. The first analysis of possible enzymatic activities of a stable protein complex was carried out in this work, revealing that the complex possesses several protease and DNase activities. The complex metalloprotease is activated by several metal ions (Zn2+ > Mn2+ > Mg2+). The relative contribution of metalloproteases (~63.4%), serine-like protease (~30.5%), and thiol protease (~6.1%) to the total protease activity of the complex was estimated. Metal-independent proteases of the complex hydrolyze proteins at trypsin-specific sites (after Lys and Arg). The complex contains both metal-dependent and metal-independent DNases. Mg2+, Mn2+, and Co2+ ions were found to strongly increase the DNase activity of the complex.

Exposure of adult sea urchin Strongylocentrotus intermedius to stranded heavy fuel oil causes developmental toxicity on larval offspring

Heavy fuel oil (HFO) spills pose serious threat to coastlines and sensitive resources. Stranded HFO that occurs along the coastline could cause long-term and massive damage to the marine environment and indirectly affect the survival of parental marine invertebrates. However, our understanding of the complex associations within invertebrates is primarily limited, particularly in terms of the toxicity effects on the offspring when parents are exposed to stranded HFO. Here, we investigated the persistent effects on the early development stage of the offspring following stranded HFO exposure on the sea urchin Strongylocentrotus intermedius. After 21 d exposure, sea urchins exhibited a significant decrease in the reproductive capacity; while the reactive oxygen species level, 3-nitrotyrosine protein level, protein carbonyl level, and heat shock proteins 70 expression in the gonadal tissues and gametes significantly increased as compared to the controls, indicating that HFO exposure could cause development toxicity on offspring in most traits of larval size. These results suggested that the stranded HFO exposure could increase oxidative stress of gonadal tissues, impair reproductive functions in parental sea urchins, and subsequently impact on development of their offspring. This study provides valuable information regarding the persistent toxicity effects on the offspring following stranded HFO exposure on sea urchins.

Novel Insights on Nitric Oxide Synthase and NO Signaling in Ascidian Metamorphosis

Nitric oxide (NO) is a pivotal signaling molecule involved in a wide range of physiological and pathological processes. We investigated NOS/NO localization patterns during the different stages of larval development in the ascidia Ciona robusta and evidenced a specific and temporally controlled pattern. NOS/NO expression starts in the most anterior sensory structures of the early larva and progressively moves towards the caudal portion as larval development and metamorphosis proceeds. We here highlight the pattern of NOS/NO expression in the central and peripheral nervous system of Ciona larvae which precisely follows the progression of neural signals of the central pattern generator necessary for the control of the movements of the larva towards the substrate. This highly dynamic localization profile perfectly matches with the central role played by NO from the first phase of settlement induction to the next control of swimming behavior, adhesion to substrate and progressive tissue resorption and reorganization of metamorphosis itself.

Accumulation and Speciation of Cobalt in Paracentrotus lividus

Since the first human release of radionuclides on Earth at the end of the Second World War, impact assessments have been implemented. Radionuclides are now ubiquitous, and the impact of local accidental release on human activities, although of low probability, is of tremendous social and economic consequences. Although radionuclide inventories (at various scales) are essential as input data for impact assessment, crucial information on physicochemical speciation is lacking. Among the metallic radionuclides of interest, cobalt-60 is one of the most important activation products generated in the nuclear industry. In this work, a marine model ecosystem has been defined because seawater and more generally marine ecosystems are final receptacles of metal pollution. A multistep approach from quantitative uptake to understanding of the accumulation mechanism has been implemented with the sea urchin Paracentrotus lividus. In a well-controlled aquarium, the day-by-day uptake of cobalt and its quantification in different compartments of the sea urchin were monitored with various conditions of exposure by combining ICP-OES analysis and γ spectrometry. Cobalt is mainly distributed following the rating intestinal tract ≫ gonads > shell spines. Cobalt speciation in seawater and inside the gonads and the intestinal tract was determined using extended X-ray absorption fine structure (EXAFS). The cobalt inside the gonads and the intestinal tract is mainly complexed by the toposome, the main protein in the sea urchin P. lividus. Complexation with purified toposome was characterized and a complexation site combining EXAFS and AIMD (ab initio molecular dynamics) was proposed implying monodentate carboxylates.

Comparative metabolome analysis provides new insights into increased larval mortality under seawater acidification in the sea urchin Strongylocentrotus intermedius

Mortality and metabolic responses of four-armed larvae of Strongylocentrotus intermedius under CO₂-induced seawater acidification were investigated. Gametes of S. intermedius were fertilized and developed to the four-armed larval stage in either current natural seawater pH levels (as Control; pH = 7.99 ± 0.01) or laboratory-controlled acidified conditions (OA₁: ΔpH = -0.3 units; OA₂: ΔpH = -0.4 units; OA₃: ΔpH = -0.5 units) according to the predictions of the Intergovernmental Panel on Climate Change (IPCC). The degrees of spicule exposure and asymmetry and mortality of four-armed larvae of S. intermedius were observed; each had a significant linearly increasing trend as the seawater pH level decreased. Comparative metabolome analysis identified a total of 87 significantly differentially expressed metabolites (SDMs, UP: 57, DOWN: 30) in OA-treated groups compared with the control group. Twenty-three SDMs, including carnitine, lysophosphatidylcholine (LPC) 18:3, lysophosphatidyl ethanolamine (LPE) 16:1, glutathione (GSH) and L-ascorbate, exhibited a linear increasing trend with decreasing seawater pH. Nine SDMs exhibited a linear decreasing trend as the seawater pH declined, including hypoxanthine, guanine and thymidine. Among all SDMs, we further mined 48 potential metabolite biomarkers responding to seawater acidification in four-armed larvae of S. intermedius. These potential metabolite biomarkers were mainly enriched in five pathways: glycerophospholipid metabolism, glutathione metabolism, purine metabolism, pyrimidine metabolism and the tricarboxylic acid cycle (TCA cycle). Our results will enrich our knowledge of the molecular mechanisms employed by sea urchins in response to CO₂-induced seawater acidification.

Transphyletic conservation of nitric oxide synthase regulation in cephalochordates and tunicates

Nitric oxide synthase is ubiquitously present in metazoans and is involved in a wide range of biological processes. Three distinct Nos genes have been so far identified in vertebrates exhibiting a complex expression pattern and transcriptional regulation. Nevertheless, although independent events of Nos duplication have been observed in several taxa, only few studies described the regulatory mechanisms responsible for their activation in non-vertebrate animals. To shed light on the mechanisms underlying neuronal-type Nos expression, we focused on two non-vertebrate chordates: the cephalochordate Branchiostoma lanceolatum and the tunicate Ciona robusta. Here, throughout transphyletic and transgenic approaches, we identified genomic regions in both species acting as Nos functional enhancers during development. In vivo analyses of Nos genomic fragments revealed their ability to recapitulate the endogenous expression territories. Therefore, our results suggest the existence of evolutionary conserved mechanisms responsible for neuronal-type Nos regulation in non-vertebrate chordates. In conclusion, this study paves the way for future characterization of conserved transcriptional logic underlying the expression of neuronal-type Nos genes in chordates.

Effects of elevated temperature on gonadal functions, cellular apoptosis, and oxidative stress in Atlantic sea urchin Arbacia punculata

Increasing seawater temperature affects growth, reproduction and development in marine organisms. In this study, we examined the effects of elevated temperatures on reproductive functions, heat shock protein 70 (HSP70) and nitrotyrosine protein (NTP, an indicator of reactive nitrogen species) expressions, protein carbonyl (PC, an indicator of oxidative stress) contents, cellular apoptosis, and coelomic fluid (CF) conditions in Atlantic sea urchin. Sea urchins were housed in six aquaria with control (24 °C) and elevated temperatures (28 °C and 32 °C) for a 7-day period. After exposure, sea urchins exhibited decreased percentages of gametes (eggs/sperm), as well as increased HSP70 and NTP expressions in eggs and spermatogenic cells, increased gonadal apoptosis, and decreased CF pH compared to controls. PC contents were also significantly increased in gonadal tissues at higher temperatures. These results suggest that elevated temperature acidifies CF, increases oxidative stress and gonadal apoptosis, and results in impairment of reproductive functions in sea urchins.

Uranium Uptake in Paracentrotus lividus Sea Urchin, Accumulation and Speciation

Uranium speciation and bioaccumulation were investigated in the sea urchin Paracentrotus lividus. Through accumulation experiments in a well-controlled aquarium followed by ICP-OES analysis, the quantification of uranium in the different compartments of the sea urchin was performed. Uranium is mainly distributed in the test (skeletal components), as it is the major constituent of the sea urchin, but in terms of quantity of uranium per gram of compartment, the following rating: intestinal tract > gonads ≫ test, was obtained. Combining both extended X-ray Absorption Spectroscopy and time-resolved laser-induced fluorescence spectroscopic analysis, it was possible to identify two different forms of uranium in the sea urchin, one in the test, as a carbonato-calcium complex, and the second one in the gonads and intestinal tract, as a protein complex. Toposome is a major calcium-binding transferrin-like protein contained within the sea urchin. EXAFS data fitting of both contaminated organs in vivo and the uranium-toposome complex from protein purified out of the gonads revealed that it is suspected to complex uranium in gonads and intestinal tract. This hypothesis is also supported by the results from two imaging techniques, i.e., Transmission Electron Microscopy and Scanning Transmission X-ray Microscopy. This thorough investigation of uranium uptake in sea urchin is one of the few attempts to assess the speciation in a living marine organism in vivo.

New Perspectives on the Evolutionary History of Vitellogenin Gene Family in Vertebrates

Vitellogenin (Vtg) is a glycolipophosphoprotein produced by oviparous and ovoviviparous species and is the precursor protein of the yolk, an essential nutrient reserve for embryonic development and early larval stages. Vtg is encoded by a family of paralog genes whose number varies in the different vertebrate lineages. Its evolution has been the subject of considerable analyses but it remains still unclear. In this work, microsyntenic and phylogenetic analyses were performed in order to increase our knowledge on the evolutionary history of this gene family in vertebrates. Our results support the hypothesis that the vitellogenin gene family is expanded from two genes both present at the beginning of vertebrate radiation through multiple independent duplication events occurred in the diverse lineages.