Biobanking of a Marine Invertebrate Model Organism: The Sea Urchin

Effects of chilling and cryoprotectants on glycans in shrimp embryos

Glycans are carbohydrates present in every organism that bind to specific molecules such as lectins, a diverse group of proteins. Glycans are vital to cell proliferation and protein trafficking. In addition, embryogenesis is a critical phase in the development of marine organisms. This study investigated the effects of chilling and cryoprotective agents (CPAs) on glycans in the embryos of Stenopus hispidus. The glycan profiles of embryos of S. hispidus at the heartbeat stage were analyzed using lectin arrays. The results of analyses revealed that mannose was the most abundant glycan in the S. hispidus embryos; mannose is crucial to cell proliferation, providing the energy required for embryonic growth. Additionally, the results reveled that chilling altered the content of several glycans, including fucose and Gla-GlcNAc. Chilling may promote monosaccharide accumulation, facilitating osmotic regulation of cells and signal molecules to aid S. hispidus embryos in adapting to cold conditions. Changes were also observed in the lectins NPA, orysata, PALa, ASA, discoidin II, discoidin I, UDA, PA-IIL, and PHA-P after the samples were treated with different CPAs. DMSO may minimize cell damage during exposure to chilling by preserving cell structures, membrane properties, and functions. The present study is the first to investigate the profiles and functions of glycans in shrimp embryos subjected to low-temperature injuries. This study enhances the understanding of cell reproduction during embryogenesis and provides valuable information for the study of glycans in embryos.

TMT-based proteomics analysis of sea urchin (Strongylocentrotus intermedius) under high temperature stress

In the context of global warming and continuous high temperatures in the northern part of China in summer, the mortality rate of Strongylocentrotus intermedius through the summer reaches 70-80 %. The protein regulatory mechanism of S. intermedius in response to high temperature stress is still unclear. In order to investigate the protein expression of S. intermedius under high temperature stress, the study was conducted with the high-temperature resistant strain of S. intermedius and the control group of S. intermedius. Tandem Mass Tag (TMT) tagging technique was applied to resolve the protein expression profile of S. intermedius in response to high temperature stress. The results showed that, compared to 15 °C，136 DEPs were screened in high-temperature resistant strain groups of S. intermedius under high temperature stress and 87 DEPs were screened in the control group of S. intermedius. There were 33 common differential proteins in the two groups, such as APOLP, HSP 70, CDC37 and CALM. Further Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways analyses revealed that the up-regulated proteins CALM and HSP70 are significantly enriched in the "Phosphatidylinositol signaling system" and "Protein processing in endoplasmic reticulum" in heat-tolerant S. intermedius strains under high temperature stress. The control group of S. intermedius DEPs were significantly enriched in protein processing in the endoplasmic reticulum. These results provide a theoretical basis for the molecular mechanism of sea urchin heat tolerance and fundamental data for sea urchin selection and breeding for high temperature tolerance.

Molecular mechanisms that regulate the heat stress response in sea urchins (Strongylocentrotus intermedius) by comparative heat tolerance performance and whole-transcriptome RNA sequencing

In the context of climate change and extreme high temperature, the commercially important sea urchin Strongylocentrotus intermedius suffers high mortality during summer in Northern China. How sea urchins respond to high temperatures is of great concern to academia and industry. How to understand the heat tolerance of sea urchin from the whole transcriptome level. In this study, the heat-resistant S. intermedius bred by our team and its control group were used as the research objects, then we applied whole-transcriptome RNA sequencing to detect differentially expressed mRNAs, microRNAs, long noncoding RNAs that respond to heat stress in the heat-resistant and control S. intermedius. A competitive endogenous RNA (ceRNA) regulatory network was constructed with predicted pairs of differentially expressed mRNAs and noncoding RNAs and revealed the molecular regulatory mechanisms in S. intermedius responding to heat stress. A functional analysis suggested that the ceRNAs were involved in basal metabolism, calcium ion transport, endoplasmic reticulum stress, and apoptosis. This is the whole-transcriptomic analysis of S. intermedius under heat stress to propose ceRNA networks that will provide a basis for studying the potential functions of long noncoding RNAs and miRNAs in the heat stress response in S. intermedius and provide a theoretical basis for the study of the molecular mechanism of sea urchins in response to environmental changes.

Rational synthesis of total damage during cryoprotectant equilibration: modelling and experimental validation of osmomechanical, temperature, and cytotoxic damage in sea urchin (Paracentrotus lividus) oocytes

Sea urchins (e.g., Paracentrotus lividus) are important for both aquaculture and as model species. Despite their importance, biobanking of urchin oocytes by cryopreservation is currently not possible. Optimized cryoprotectant loading may enable novel vitrification methods and thus successful cryopreservation of oocytes. One method for determining an optimized loading protocol uses membrane characteristics and models of damage, namely osmomechanical damage, temperature damage (e.g., chill injury) and cytotoxicity. Here we present and experimentally evaluate existing and novel models of these damage modalities as a function of time and temperature. In osmomechanical damage experiments, oocytes were exposed for 2 to 30 minutes in hypertonic NaCl or sucrose supplemented seawater or in hypotonic diluted seawater. In temperature damage experiments, oocytes were exposed to 1.7 °C, 10 °C, or 20 °C for 2 to 90 minutes. Cytotoxicity was investigated by exposing oocytes to solutions of Me2SO for 2 to 30 minutes. We identified a time-dependent osmotic damage model, a temperature-dependent damage model, and a temperature and time-dependent cytotoxicity model. We combined these models to estimate total damage during a cryoprotectant loading protocol and determined the optimal loading protocol for any given goal intracellular cryoprotectant concentration. Given our fitted models, we find sea urchin oocytes can only be loaded to 13% Me2SO v/v with about 50% survival. This synthesis of multiple damage modalities is the first of its kind and enables a novel approach to modelling cryoprotectant equilibration survival for cells in general.

Sexually dimorphic expression of foxl2 in the sea urchin (Mesocentrotus nudus)

Sea urchin (Mesocentrotus nudus) is an important economically mariculture species in several Asian countries, and gonads are the sole edible parts for people. In addition to commercial value, it is an excellent model for studying gonadal development, sex determination and sex differentiation. Identify sex-related genes is an effective way to reveal the molecular mechanism of gonadal development. In the present study, the foxl2 homologous gene was identified in M. nudus. Foxl2 is not a maternal factor, and is detected for the first time in two-arm stages. Additionally, the expression of foxl2 in the testis is higher than in the ovaries at the same developmental stages. The foxl2 transcripts were specifically enriched in the cytoplasm of germ cellsboth in the ovary and testis, but their proteins were more concentrated in the area near the oocyte nucleus. Overall, this study contributes to our understanding of the dynamic and sexually dimorphic expression pattern of foxl2 and provide a useful germ cell marker during gametogenesis in sea urchin.

Handling, Reproducing and Cryopreserving Five European Sea Urchins (Echinodermata, Klein, 1778) for Biodiversity Conservation Purposes

In this work, five local sea urchin species found in European waters were studied. Four were regular species: Sphaerechinus granularis, Psammechinus miliaris, Echinus esculentus (Linnaeus, 1758) and the edible sea urchin Paracentrotus lividus; and one was an irregular species, Echinocardium cordatum. These five species of sea urchins have been studied regarding their fertility, toxicity of cryoprotecting agents, cryopreservation of different cell types and chilling injury. The baseline fertility is similar in P. lividus, P. miliaris and S. granularis. Nonetheless, the sperm:egg ratio, contact time and development of the fertilization envelope would need to be studied further on a case-by-case basis. Sperm can be maintained inactively in the gonad (4 °C), and oocytes also maintain quality in sea water (4 °C), even after 72 h. Sperm was cryopreserved for four species with some post-thaw intra specific variability, and embryo cryopreservation was only possible for S. granularis. Overall, this study provided a wider vision of the biology and reproduction of these species that will help us develop tools for their biodiversity conservation through cryopreservation.

Long-term study on survival and development of successive generations of Mytilus galloprovincialis cryopreserved larvae

Shellfish aquaculture needs the development of new tools for the improvement of good practices avoiding the reliance on natural spat collection to increase production efficiently. The aim of this work was to improve the cryopreservation protocol for Mytilus galloprovincialis larvae described in Paredes et al. (in: Wolkers, Oldenhof (eds) Cryopreservation and freeze-drying protocol, methods in molecular biology, Humana Press, 2021, pp 2180, 10.1007/978-1-0716-0783-1_18). Moreover, the capability of producing adult mussels from cryopreserved 72 h-old D-larvae and potential long-term effects of cryopreservation through progenies were evaluated. The selection of 72-h old D-larvae for cryopreservation yielded 75% of recovery, higher than 50% from trochophores. The best combination was 10% Ethylene–Glycol + 0.4 M Trehalose in Filtered Sea Water (FSW) with cooling at − 1 °C/min and a water bath at 35 °C for thawing. Sucrose (SUC) solutions did not improve larval recovery (p > 0.05). At settlement, 5.26% of cryopreserved F1 larvae survived and over 70% settled. F2 cryopreservation produced 0.15% survival of spat and settlement varied from 35 to 50%. The delay of shell size showed on cryopreserved larvae declined throughout larval rearing without significant differences with controls from settlement point (p > 0.05). Long-term experiments showed that it is possible to obtain adult mussels from cryopreserved larvae and this tool does not compromise the quality of following progenies, neither for cryopreservation nor post-thawing development of them.

Expression Regulation Mechanisms of Sea Urchin (Strongylocentrotus intermedius) Under the High Temperature: New Evidence for the miRNA-mRNA Interaction Involvement

In the context of global warming and continuous high temperatures in the northern part of China during summer, the mortality rate of our main breeding species, Strongylocentrotus intermedius, reached 80% in 2020. How sea urchins respond to high temperatures is of great concern to academia and industry. In this study, we examined the antioxidant enzyme activities of different color tube-footed sea urchins under heat stress and compared their transcriptome and microRNA (miRNA) profiles using RNA-Seq. The results showed that the antioxidant enzyme activities of sea urchins were altered by thermal stress, and the changes in peroxidase activities of red tube-footed sea urchins were particularly significant. Investigations revealed that 1,079 differentially expressed genes (DEGs), 11 DE miRNAs, and 104 “DE miRNA-DEG” pairs in total were detected in sea urchins under high temperature stress. Several mRNA and miRNAs were significantly changed (e.g. HSP70, DnaJ11, HYAL, CALR, miR-184-p5, miR-92a, miR-92c, and miR-124-p5), suggesting these genes and miRNAs exerted important functions in response to high temperature. At the transcriptional level, red tube-footed sea urchins were found to be more sensitive to high temperature and could respond to high temperature rapidly. DE miRNA-mRNA network showed that miR-92b-3p and PC-5p-7420 were the most corresponding miRNAs. Five mRNAs (DnaJ11, SAR1B, CALR, HYOU1, TUBA) may be potential markers of sea urchin response to high temperature. Possible interaction between miRNA-mRNA could be linked to protein folding in the endoplasmic reticulum, Phagosomes, and calcium transport. This study provides a theoretical basis for the molecular mechanism of sea urchin heat tolerance and information that will aid in the selection and breeding of sea urchins with high temperature tolerance.

Environmental Risk Assessment of Vehicle Exhaust Particles on Aquatic Organisms of Different Trophic Levels

Vehicle emission particles (VEPs) represent a significant part of air pollution in urban areas. However, the toxicity of this category of particles in different aquatic organisms is still unexplored. This work aimed to extend the understanding of the toxicity of the vehicle exhaust particles in two species of marine diatomic microalgae, the planktonic crustacean Artemia salina, and the sea urchin Strongylocentrotus intermedius. These aquatic species were applied for the first time in the risk assessment of VEPs. Our results demonstrated that the samples obtained from diesel-powered vehicles completely prevented egg fertilization of the sea urchin S. intermedius and caused pronounced membrane depolarization in the cells of both tested microalgae species at concentrations between 10 and 100 mg/L. The sample with the highest proportion of submicron particles and the highest content of polycyclic aromatic hydrocarbons (PAHs) had the highest growth rate inhibition in both microalgae species and caused high toxicity to the crustacean. The toxicity level of the other samples varied among the species. We can conclude that metal content and the difference in the concentrations of PAHs by itself did not directly reflect the toxic level of VEPs, but the combination of both a high number of submicron particles and high PAH concentrations had the highest toxic effect on all the tested species.

Development of alternative and sustainable methodologies in laboratory research on sea urchin gametes

The aim of the present work is to develop a laboratory-scaled methodology for an on-demand supply of semen from the sea urchin Paracentrotus lividus. Firstly, sea urchin specimens were acclimatized to the long-term rearing in a recirculating aquaculture system and gonad maturation was obtained under controlled conditions. Semen samples were then collected from mature sea urchins and cryopreserved. Finally, post-thawing motility was evaluated, to verify whether the cryopreserved semen had maintained enough viability to be used in laboratory activities. The post-thawing motility parameters remained quite unchanged for up to 60 min after activation; moreover, the semen even retained the ability of motility activation for 60 min after thawing. This motility pattern makes the use of cryopreserved semen a feasible option in spermiotoxicity bioassays. The preliminary ecotoxicity test, carried out using motility parameters as endpoints, showed sensitivity levels to cadmium falling in the same order of magnitude as those recorded for fresh sea urchin semen and for cryopreserved sea bream semen. . Therefore, semen samples produced and stored according to the developed methodology described in this paper, can be considered a promising and sustainable alternative to those collected from mature sea urchins harvested in the field.

High-quality RNA extraction from the sea urchin Paracentrotus lividus embryos

The sea urchin Paracentrotus lividus (Lamarck, 1816) is a keystone herbivore in the Mediterranean Sea due to its ability to transform macroalgal-dominated communities into barren areas characterized by increased cover of bare substrates and encrusting coralline algae, reduced biodiversity and altered ecosystem functions. P. lividus is also an excellent animal model for toxicology, physiology and biology investigations having been used for more than a century as a model for embryological studies with synchronously developing embryos which are easy to manipulate and analyze for morphological aberrations. Despite its importance for the scientific community, the complete genome is still not fully annotated. To date, only a few molecular tools are available and a few Next Generation Sequencing (NGS) studies have been performed. Here we aimed at setting-up an RNA extraction method to obtain high quality and sufficient quantity of RNA for NGS from P. lividus embryos at the pluteus stage. We compared five different RNA extraction protocols from four different pools of plutei (500, 1000, 2500 and 5000 embryos): TRIzol®, and four widely-used Silica Membrane kits, GenElute™ Mammalian Total RNA Miniprep Kit, RNAqueous® Micro Kit, RNeasy® Micro Kit and Aurum™ Total RNA Mini Kit. The quantity of RNA isolated was evaluated using NanoDrop. The quality, considering the purity, was measured as A260/A280 and A260/230 ratios. The integrity was measured by RNA Integrity Number (RIN). Our results demonstrated that the most efficient procedures were GenElute, RNeasy and Aurum, producing a sufficient quantity of RNA for NGS. The Bioanalyzer profiles and RIN values revealed that the most efficient methods guaranteeing for RNA integrity were RNeasy and Aurum combined with an initial preservation in RNAlater. This research represents the first attempt to standardize a method for high-quality RNA extraction from sea urchin embryos at the pluteus stage, providing a new resource for this established model marine organism.

The contribution of apoptosis and necrosis in freezing injury of sea urchin embryonic cells

Sea urchins have recently been reported to be a promising tool for investigations of oxidative stress, UV light perturbations and senescence. However, few available data describe the pathway of cell death that occurs in sea urchin embryonic cells after cryopreservation. Our study is focused on the morphological and functional alterations that occur in cells of these animals during the induction of different cell death pathways in response to cold injury. To estimate the effect of cryopreservation on sea urchin cell cultures and identify the involved cell death pathways, we analyzed cell viability (via trypan blue exclusion test, MTT assay and DAPI staining), caspase activity (via flow cytometry and spectrophotometry), the level of apoptosis (via annexin V-FITC staining), and cell ultrastructure alterations (via transmission electron microscopy). Using general caspase detection, we found that the level of caspase activity was low in unfrozen control cells, whereas the number of apoptotic cells with activated caspases rose after freezing-thawing depending on cryoprotectants used, also as the number of dead cells and cells in a late apoptosis. The data using annexin V-binding assay revealed a very high apoptosis level in all tested samples, even in unfrozen cells (about 66%). Thus, annexin V assay appears to be unsuitable for sea urchin embryonic cells. Typical necrotic cells with damaged mitochondria were not detected after freezing in sea urchin cell cultures. Our results assume that physical cell disruption but not freezing-induced apoptosis or necrosis is the predominant reason of cell death in sea urchin cultures after freezing-thawing with any cryoprotectant combination.