Cell signalling during sea urchin development: a model for assessing toxicity of environmental contaminants

On Oscillations in the External Electrical Potential of Sea Urchins

Sea urchins display complex bioelectric activity patterns, even with their decentralized nervous system. Electrophysiological recordings showed distinct spiking patterns. The baseline potential was about 8.80 mV. It had transient spikes with amplitudes up to 21.05 mV. We observed many types of depolarization events. They included burst-like activity and prolonged state fluctuations lasting several seconds. Frequency domain analysis showed a power-law behavior. It had a scaling exponent of 6.21 ± 0.06, indicating critical dynamics. The analysis showed potential variations between 3.69 and 21.05 mV. The oscillation periods ranged from 4 to 3102 s. The varied timing of bioelectric signals suggests that these organisms can process information. This challenges traditional views of neural computation in simpler animals. These findings provide quantitative insights into the complex signaling mechanisms of the sea urchin's distributed nervous system.

Inhibitory effects of neurotoxin β-N-methylamino-L-alanine on fertilization and early development of the sea urchin Lytechinus pictus

Neurotoxin β-N-methylamino-L-alanine (BMAA) has been widely detected in diverse aquatic organisms and hypothesized as an environmental risk to neurodegenerative diseases in humans. However, the knowledge of its toxicity to marine organisms requires attention. In the present study, embryos and sperm of the sea urchin, Lytechinus pictus, were used to assess the toxicity of BMAA. Effects of BMAA on fertilization and development of sea urchin embryos were measured, and its impacts on efflux transport of sea urchin blastula were also assayed. Results demonstrated that the fertilization and development of embryos were significantly inhibited by high concentrations of BMAA above 300 μg L^-1. The EC₅₀ values indicated by active swimming larvae and total larvae numbers at 96 HPF (hours post fertilization) were 165 μg L^-1 (1.4 μmol L^-1) and 329 μg L^-1 (2.8 μmol L^-1), respectively. Additionally, sperm exposed to BMAA for 10 min significantly reduced the fertilization ratio of sea urchin eggs. However, the ABC transport activity on the cytomembrane of sea urchin blastula was not inhibited by the presence of BMAA at 50 μg L^-1, even up to 500 μg L^-1. Abnormal division and developmental malformations occurred at different developmental stages for sea urchin embryos exposed to BMAA at 500 μg L^-1. The inhibitory effects of BMAA on sea urchin embryos were reported at the first time in this study, for which the toxicological mechanisms will be explored in future studies.

Developmental effects of the protein kinase inhibitor kenpaullone on the sea urchin embryo

The selection and validation of bioactive compounds require multiple approaches, including in-depth analyses of their biological activity in a whole-animal context. We exploited the sea urchin embryo in a rapid, medium-scale range screening to test the effects of the small synthetic kinase inhibitor kenpaullone. We show that sea urchin embryos specifically respond to this molecule depending on both dose and timing of administration. Phenotypic effects of kenpaullone are not immediately visible, since this molecule affects neither the fertilization nor the spatial arrangement of blastomeres at early developmental stages. Nevertheless, kenpaullone exposure from the beginning of embryogenesis profoundly perturbs specification, detachment from the epithelium, and migration of the primary mesenchyme cells, thus affecting the whole embryonic epithelial mesenchymal transition process. Our results reaffirm the sea urchin embryo as an excellent and sensitive in vivo system, which provides straightforward and rapid response to external stimuli.

De novo transcriptome sequencing and comparative analysis to discover genes involved in ovarian maturity in Strongylocentrotus nudus

Strongylocentrotus nudus is an edible sea urchin, mainly harvested in China. Correlation studies indicated that S. nudus with larger diameter have a prolonged marketing time and better palatability owing to their precocious gonads and extended maturation process. However, the molecular mechanism underlying this phenomenon is still unknown. Here, transcriptome sequencing was applied to study the ovaries of adult S. nudus with different shell diameters to explore the possible mechanism. In this study, four independent cDNA libraries were constructed, including two from the big size urchins and two from the small ones using a HiSeq™2500 platform. A total of 88,581 unigenes were acquired with a mean length of 1354bp, of which 66,331 (74.88%) unigenes could be annotated using six major publicly available databases. Comparative analysis revealed that 353 unigenes were differentially expressed (with log2(ratio)≥1, FDR≤0.001) between the two groups. Of these, 20 differentially expressed genes (DEGs) were selected to confirm the accuracy of RNA-seq data by quantitative real-time RT-PCR. Furthermore, gene ontology and KEGG pathway enrichment analyses were performed to find the putative genes and pathways related to ovarian maturity. Eight unigenes were identified as significant DEGs involved in reproduction related pathways; these included Mos, Cdc20, Rec8, YP30, cytochrome P450 2U1, ovoperoxidase, proteoliaisin, and rendezvin. Our research fills the gap in the studies on the S. nudus ovaries using transcriptome analysis.

Early appearance and possible functions of non-neuromuscular cholinesterase activities

The biological function of the cholinesterase (ChE) enzymes has been studied since the beginning of the twentieth century. Acetylcholinesterase plays a key role in the modulation of neuromuscular impulse transmission in vertebrates, while in invertebrates pseudo cholinesterases are preeminently represented. During the last 40 years, awareness of the role of ChEs role in regulating non-neuromuscular cell-to-cell interactions has been increasing such as the ones occurring during gamete interaction and embryonic development. Moreover, ChE activities are responsible for other relevant biological events, including regulation of the balance between cell proliferation and cell death, as well as the modulation of cell adhesion and cell migration. Understanding the mechanisms of the regulation of these events can help us foresee the possible impact of neurotoxic substances on the environmental and human health.

Localization and properties of cholinesterases in the common prawn (Palaemon serratus): A kinetic-histochemical study

Due to the diversity in biochemical properties and tissue distribution of cholinesterase (ChE) enzymes, a characterization should be performed before they are used as biomarkers for monitoring pesticide contamination. In this study we investigate the distribution of ChEs and their kinetic properties in diverse tissues of the common prawn Palaemon serratus. The results concerning the histochemical localization of ChEs suggest that the highest amount of ChE activity occurs in prawn eyes, followed by the brain, gills, and digestive tract. Negligible staining was observed in the muscle. We describe the kinetic properties of ChEs in eyes, gills, and hepatopancreas, investigating their substrate preferences with different thiocholine esters and their sensitivity to inhibition with selective inhibitors. The results suggest that the studied enzymes are ChEs and not nonspecific esterases, due to their apparent affinity for choline esters, with a distinct preference for the substrate acetylthiocholine, and their high sensitivity to inhibition by eserine sulfate. P. serratus eyes can be considered the best tissue for recovery of ChE enzyme: this tissue is easy to isolate, it expresses high levels of ChE, and the enzyme shows properties of a vertebrate AChE.

Sea urchin development: an alternative model for mechanistic understanding of neurodevelopment and neurotoxicity

Echinoderm early developmental stages might supply a good tool for toxicity testing in different fields, ranging from environment to food contamination, and in full respect of the 3Rs objectives (reduction, refinement, and replacement of animal experiments) that will eventually lead to the replacement of high vertebrate animal testing in toxicology. Sea urchin is one of the few organismic models considered by the European Agency for Alternative models. Actually, sea urchin embryonic development has been studied for over a century, and the complex nets of intercellular communications leading to the different events are well known, as well the possibility for environmental molecules and their residuals to interfere with such communications, causing developmental anomalies. In particular, the main goal of toxicologists since several years has been to establish a correlation between the cell-to-cell communications occurring during different developmental events and the signals occurring during neurogenesis, with the aim to pursue a mechanistic understanding of these processes and their deviations caused by stressors from different sources.

Responses of marine organisms to physical and chemical impacts

Studies on the effects of a variety of exogenous and anthropogenic environmental factors, including endocrine disruptors, heavy metals, UV light, high temperature, and others, on marine organisms have been presented at the 2nd Bilateral Seminar Italy-Japan held in November 2006. Reports were discussed in order to reveal the current situation of marine ecosystems, aiming at evaluation and prediction of environmental risks.