Matrix and mineral in the sea urchin larval skeleton

Localization and origins of juvenile skeletogenic cells in the sea urchin Lytechinuspictus

The development of the sea urchin larval body plan is well understood from extensive studies of embryonic patterning. However, fewer studies have investigated the late larval stages during which the unique pentaradial adult body plan develops. Previous work on late larval development highlights major tissue changes leading up to metamorphosis, but the location of specific cell types during juvenile development is less understood. Here, we improve on technical limitations by applying highly sensitive hybridization chain reaction fluorescent in situ hybridization (HCR-FISH) to the fast-developing and transparent sea urchin Lytechinus pictus, with a focus on skeletogenic cells. First, we show that HCR-FISH can be used in L. pictus to precisely localize skeletogenic cells in the rudiment. In doing so, we provide a detailed staging scheme for the appearance of skeletogenic cells around the rudiment prior to and during biomineralization and show that many skeletogenic cells unassociated with larval rods localize outside of the rudiment prior to localizing inside. Second, we show that downstream biomineralization genes have similar expression patterns during larval and juvenile skeletogenesis, suggesting some conservation of skeletogenic mechanisms during development between stages. Third, we find co-expression of blastocoelar and skeletogenic cell markers around juvenile skeleton located outside of the rudiment, which is consistent with data showing that cells from the non-skeletogenic mesoderm embryonic lineage contribute to the juvenile skeletogenic cell lineage. This work sets the foundation for subsequent studies of other cell types in the late larva of L. pictus to better understand juvenile body plan development, patterning, and evolution.

Composite material in the sea urchin Cidaris rugosa: ordered and disordered micrometre-scale bicontinuous geometries

The sponge-like biomineralized calcite materials found in echinoderm skeletons are of interest in terms of both structure formation and biological function. Despite their crystalline atomic structure, they exhibit curved interfaces that have been related to known triply periodic minimal surfaces. Here, we investigate the endoskeleton of the sea urchin Cidaris rugosa that has long been known to form a microstructure related to the Primitive surface. Using X-ray tomography, we find that the endoskeleton is organized as a composite material consisting of domains of bicontinuous microstructures with different structural properties. We describe, for the first time, the co-occurrence of ordered single Primitive and single Diamond structures and of a disordered structure within a single skeletal plate. We show that these structures can be distinguished by structural properties including solid volume fraction, trabeculae width and, to a lesser extent, interface area and mean curvature. In doing so, we present a robust method that extracts interface areas and curvature integrals from voxelized datasets using the Steiner polynomial for parallel body volumes. We discuss these very large-scale bicontinuous structures in the context of their function, formation and evolution.

Elemental compositions of sea urchin larval cell vesicles evaluated by cryo-STEM-EDS and cryo-SEM-EDS

During spicule formation in sea urchin larvae, calcium ions translocate within the primary mesenchymal cells (PMCs) from endocytosed seawater vacuoles to various organelles and vesicles where they accumulate, and subsequently precipitate. During this process, calcium ions are concentrated by more than three orders of magnitude, while other abundant ions (Na, Mg) must be removed. To obtain information about the overall ion composition in the vesicles, we used quantitative cryo-SEM-EDS and cryo-STEM-EDS analyzes. For cryo-STEM-EDS, thin (500 nm) frozen hydrated lamellae of PMCs were fabricated using cryo-focused ion beam-SEM. The lamellae were then loaded into a cryo-TEM, imaged and the ion composition of electron dense bodies was measured. Analyzes performed on 18 Ca-rich particles/particle clusters from 6 cells contained Ca, Na, Mg, S and P in different ratios. Surprisingly, all the Ca-rich particles contained P in amounts up to almost 1:1 of Ca. These cryo-STEM-EDS results were qualitatively confirmed by cryo-SEM-EDS analyzes of 310 vesicles, performed on high pressure frozen and cryo-planed samples. We discuss the advantages and limitations of the two techniques, and their potential applicability, especially to study ion transport pathways and ion trafficking in cells involved in mineralization. STATEMENT OF SIGNIFICANCE: The 'inorganic side of life', encompassing ion trafficking and ion storage in soft tissues of organisms, is a generally overlooked problem. Addressing such a problem becomes possible through the application of innovative techniques, performed in cryogenic conditions, which preserve the tissues in quasi-physiological state. We developed here a set of analytical tools, cryo-SEM-EDS, and cryo-STEM-EDS, which allow reconstructing the ion composition inside vesicles in sea urchin larval cells, on their way to deposit mineral in the skeletons. The techniques are complex, and we evaluate here the advantages and disadvantages of each technique. The methodologies that we are developing here can be applied to other cells and other pathways as well, eventually leading to quantitative elemental analyzes of tissues under cryogenic conditions.

Ordered stereom structure in sea urchin tubercles: High capability for energy dissipation

Tubercles in sea urchin shells serve as a base on the test plates connecting the spine; these undergo compressive or impact stress from the spines. As the volume fraction of the ordered stereom structure in a tubercle increases, the compressive load-displacement curves are gradually characterized by the typical behavior of ceramic foams. Although this ordered stereom structure only exhibits an average porosity of 50.6%, it also exhibits high fracture resistance and energy dissipation capacity. Such remarkable behavior of the ordered stereom structure is attributed to its unique hierarchical microstructure. Specifically, at the macroscale, the stereom structure is periodic. It has uniformly distributed pores that are typically round, which can effectively reduce the stress concentration around the pores, and the ordered arrangement of the trabeculae along the axial direction of the tubercle bears the most compressive stress. The trabeculae present a bottleneck shape with a specific dimension, ensuring the best fracture resistance with a relatively higher porosity. Furthermore, crack deflection in the trabeculae changes the local fracture mode of the mineral, thereby increasing the crack surface area. STATEMENT OF SIGNIFICANCE: The connecting bases of the spines in sea urchin shell, known as tubercle, effectively undergo the compressive stress or impact stress from the spines. An ordered stereom structure is found in the tubercle, and it shows an excellent fracture resistance and energy dissipation capacity. Such a fantastic behavior of the ordered stereom structure mainly takes advantage of its unique hierarchical microstructure. The stereom structure presents a periodic structure on macroscale, the trabeculae show a bottleneck shape with a specific dimension to guarantee the best fracture resistance with a relatively higher porosity, and the soft fillers among CaCO₃ nanoparticles in a trabecula cause consecutive crack deflections.

Crystallographic control of the fabrication of an extremely sophisticated shell surface microornament in the glass scallop Catillopecten

The external surface microornament of the glass scallops Catillopecten natalyae and malyutinae is made by calcitic spiny projections consisting of a stem that later divides into three equally spaced and inclined branches (here called aerials). C. natalyae contains larger and smaller aerials, whereas C. malyutinae only secreted aerials of the second type. A remarkable feature is that aerials within each type are fairly similar in size and shape and highly co-oriented, thus constituting a most sophisticated microornament. We demonstrate that aerials are single crystals whose morphology is strongly controlled by the crystallography, with the stem being parallel to the c-axis of calcite, and the branches extending along the edges of the {104} calcite rhombohedron. They grow epitaxially onto the foliated prisms of the outer shell layer. The co-orientation of the prisms explains that of the aerials. We have developed a model in which every aerial grows within a periostracal pouch. When this pouch reaches the growth margin, the mantle initiates the production of the aerial. Nevertheless, later growth of the aerial is remote, i.e. far from the contact with the mantle. We show how such an extremely sophisticated microornament has a morphology and co-orientation which are determined by crystal growth.

Complexation reduces nickel toxicity to purple sea urchin embryos (Strongylocentrotus purpuratus), a test of biotic ligand principles in seawater

The potential for Ni toxicity in seawater is of concern because of mining and processing activities in coastal regions. Determining Ni speciation is vital to understanding and predicting Ni toxicity and for bioavailability-based nickel risk assessment. The goal of this study was to characterize the complexation of Ni in relation to toxicity using embryological development of purple sea urchin (S. purpuratus). It was predicted that free ion [Ni2+] would be a better predictor of toxicity than total dissolved Ni concentrations (NiD). Synthetic ligands with known logKf values (Ethylenediaminetetraacetic acid (EDTA), Nitrilotriacetic acid (NTA), tryptophan (TRP), glutamic acid (GA), histidine (HD), and citric acid (CA)) were used to test the assumptions of the biotic ligand model (BLM) for Ni in seawater. [NiD] was measured by graphite furnace atomic absorption spectroscopy (GFAAS) and Ni2+ was first quantified using the ion-exchange technique (IET) and then concentrations were measured by GFAAS; [Ni2+] was also estimated using aquatic geochemistry modelling software (Visual Minteq). The mean EC50 values for [NiD] in unmodified artificial seawater control was 3.6 µM (95% CI 3.0-4.5) [211 µg/L 95% CI 176-264] and the addition of ligands provided protection, up to 6.5-fold higher [NiD] EC50 for EDTA. Compared to the control, measured EC50 values based on total dissolved nickel were higher in the presence of ligands. As predicted by BLM theory, [Ni2+] was a better predictor of Ni toxicity with 17% variability in EDTA and CA media while there was 72% variability in the prediction of Ni toxicity with total dissolved Ni. The results of this research provide support for the application of BLM- based prediction models for estimating Ni impacts in seawater.

Influence of environmentally relevant concentrations of Zn, Cd and Ni and their binary mixtures on metal uptake, bioaccumulation and development in larvae of the purple sea urchin Strongylocentrotus purpuratus

Metal accumulation, disturbance of Ca²⁺ homeostasis, and occurrence of abnormalities are well-established consequences of single metal exposure during early development stages of sea urchins. However, the effects caused by low concentrations of metals and metal mixtures need to be better understood in marine invertebrates. Therefore, the present study investigated the effects of environmentally relevant concentrations of Zn (9 μg/L), Cd (30 μg/L) and Ni (5 μg/L) in single and binary exposures (Zn + Cd, Cd + Ni and Ni + Zn) to the early life stages of the purple sea urchin Strongylocentrotus purpuratus. Endpoints checked in all treatments after 48-h exposure were unidirectional metal influx rates, bioaccumulation, and Ca²⁺ influx rates. Additionally, the presence of abnormal larvae and developmental delay was evaluated at 24 h, 48 h and 72 h of exposure. Unidirectional influx rates of all three metals were significantly higher than control background rates in all single exposures and binary mixtures, and were generally not different between them. Net accumulation (body burden) of both Zn and Cd increased significantly as a result of their respective single exposures, while Ni accumulation decreased considerably. When Zn or Cd were presented in binary exposures with other metals, the net accumulations of Zn or Cd were reduced relative to single exposures to these metals, whereas this did not occur for Ni accumulation. Thus, bioaccumulation proved to be a better metric than influx rate measurements to analyze metal competition at a whole organism level at these low metal concentrations. Short-term Ca²⁺ influx also did not appear to be a sensitive metric, as the measured rates did not vary among all single and binary exposures, with the exception of a lower rate in Ni + Zn binary exposure. A critical aspect observed was the relationship between bioaccumulation versus influx measurements, which proved positive for Cd, but negative for Zn and Ni, demonstrating possible capacities for both Zn and Ni regulation by sea urchin larvae. Increases in larval abnormalities relative to controls occurred only after binary mixtures, starting at 48 h exposure and maintained until 72 h. However, delay of the sea urchin development by the presence of gastrula stage at 72 h exposure occurred in Zn and Ni single exposures and all metal mixtures, with very high abnormal development when Ni was present.

Lattice Shrinkage by Incorporation of Recombinant Starmaker-Like Protein within Bioinspired Calcium Carbonate Crystals

The biological mediation of mineral formation (biomineralization) is realized through diverse organic macromolecules that guide this process in a spatial and temporal manner. Although the role of these molecules in biomineralization is being gradually revealed, the molecular basis of their regulatory function is still poorly understood. In this study, the incorporation and distribution of the model intrinsically disordered starmaker-like (Stm-l) protein, which is active in fish otoliths biomineralization, within calcium carbonate crystals, is revealed. Stm-l promotes crystal nucleation and anisotropic tailoring of crystal morphology. Intracrystalline incorporation of Stm-l protein unexpectedly results in shrinkage (and not expansion, as commonly described in biomineral and bioinspired crystals) of the crystal lattice volume, which is described herein, for the first time, for bioinspired mineralization. A ring pattern was observed in crystals grown for 48 h; this was composed of a protein-enriched region flanked by protein-depleted regions. It can be explained as a result of the Ostwald-like ripening process and intrinsic properties of Stm-l, and bears some analogy to the daily growth layers of the otolith.

The unique biomineralization transcriptome and proteome of Lytechinus variegatus teeth

BACKGROUND

Matrix-regulated biomineralization involves the specific nucleation and growth of mineral phases within or upon preformed structured organic matrices. We hypothesized that there might be a general mechanism whereby anionic, phosphorylated mineral ion-binding proteins assist in specifically locating the mineral ions with respect to the mineralizing structural organic matrix. Here we extended these studies to invertebrate mineralization in Lytechinus variegatus (Lv) teeth.

MATERIALS AND METHODS

The tooth proteins were extracted and the phosphoproteins occluded in the mineral were enriched by passage through a ProQ Diamond phosphoprotein enrichment column, and subjected to MS/MS analysis. A Lv RNA-seq derived transcriptome database was generated. The MS/MS data found 25 proteins previously classified as "Predicted uncharacterized proteins" and many of the spicule matrix proteins. As these 25 proteins were also identified with the transcriptome analysis, and were thus no longer "hypothetical" but real proteins in the Lv tooth. Each protein was analyzed for the presence of a signal peptide, an acidic pI≤4, and the ability to be phosphorylated.

RESULTS

Four new Lv tooth specific Pro-Ala-rich proteins were found, representing a new class of proteins.

CONCLUSION

The tooth is different from the spicules and other urchin skeletal elements in that only the tooth contains both "high" and "very high" magnesium calcite, [Ca(1-X) Mg(X) CO3], where X is the mole fraction of Mg. We speculate that our newly discovered proline-alanine rich proteins, also containing sequences of acidic amino acids, may be involved in the formation of high magnesium and very high magnesium calcite.

A comparative study of repeated sequences in the SM50 gene of some sea urchins

Spicule matrix proteins of sea urchin embryo are the specific products of the micromere / primary mesenchyme cell (PMC) lineage, and are considered to be involved in spicule formation (Wilt, 1999). One of these proteins, SM50, has been described for three species: Strongylocentrotus purpuratus (SP), Lytechinus pictus (Lp) and Hemicentrotus pulcherrimus (Hp) (for references see Wilt, 1999). The nucleotide and amino acid sequences are well conserved in these species. SM50 proteins of these species have repetitive amino acid sequences in the carboxyl-terminal half of the proteins. Therefore, examination of SM50 sequences, especially the repetitive sequence region, in various species will help an understanding of the process of sea urchin ontogeny and evolution. In this study we tried to amplify, by PCR, the SM50 sequences of species for which no sequence data are reported.

Total DNA was extracted from the sperm of sea urchins by standard procedures. The purified DNA was subjected to PCR to amplify the repetitive amino acid region and its upstream region. The primers were designed based on the highly conserved sequences in the reported SM50 as Consensus-Degenerate Hybrid Oligonucleotide Primers (Rose et al., 1997). The amplified products were gel-purified, and sequenced using ABI PRISM 310 Genetic Analyzer using PCR primers. The determined nucleotide sequences were translated into amino acid sequences and compared among species with a phylogenetic tree constructed by the neighbour-joining method. For indirect immunofluorescent staining, embryos were fixed with 70% methanol and reacted with rabbit antiserum against recombinant SM50 protein.

Alteration of neurotransmission and skeletogenesis in sea urchin Arbacia lixula embryos exposed to copper oxide nanoparticles

The extensive use of copper oxide nanoparticles (CuO NPs) in many applications has raised concerns over their toxicity on environment and human health. Herein, the embryotoxicity of CuO NPs was assessed in the black sea urchin Arbacia lixula, an intertidal species commonly present in the Mediterranean. Fertilized eggs were exposed to 0.7, 10 and 20ppb of CuO NPs, until pluteus stage. Interferences with the normal neurotransmission pathways were observed in sea urchin embryos. In detail, evidence of cholinergic and serotoninergic systems affection was revealed by dose-dependent decreased levels of choline and N-acetyl serotonin, respectively, measured by nuclear magnetic resonance (NMR)-based metabolomics, applied for the first time to our knowledge on sea urchin embryos. The metabolic profile also highlighted a significant CuO NP dose-dependent increase of glycine, a component of matrix proteins involved in the biomineralization process, suggesting perturbed skeletogenesis accordingly to skeletal defects in spicule patterning observed previously in the same sea urchin embryos. However, the expression of skeletogenic genes, i.e. SM30 and msp130, did not differ among groups, and therefore altered primary mesenchyme cell (PMC) migration was hypothesized. Other unknown metabolites were detected from the NMR spectra, and their concentrations found to be reflective of the CuO NP exposure levels. Overall, these findings demonstrate the toxic potential of CuO NPs to interfere with neurotransmission and skeletogenesis of sea urchin embryos. The integrated use of embryotoxicity tests and metabolomics represents a highly sensitive and effective tool for assessing the impact of NPs on aquatic biota.

Modeling and simulation of protein-surface interactions: achievements and challenges

Understanding protein-inorganic surface interactions is central to the rational design of new tools in biomaterial sciences, nanobiotechnology and nanomedicine. Although a significant amount of experimental research on protein adsorption onto solid substrates has been reported, many aspects of the recognition and interaction mechanisms of biomolecules and inorganic surfaces are still unclear. Theoretical modeling and simulations provide complementary approaches for experimental studies, and they have been applied for exploring protein-surface binding mechanisms, the determinants of binding specificity towards different surfaces, as well as the thermodynamics and kinetics of adsorption. Although the general computational approaches employed to study the dynamics of proteins and materials are similar, the models and force-fields (FFs) used for describing the physical properties and interactions of material surfaces and biological molecules differ. In particular, FF and water models designed for use in biomolecular simulations are often not directly transferable to surface simulations and vice versa. The adsorption events span a wide range of time- and length-scales that vary from nanoseconds to days, and from nanometers to micrometers, respectively, rendering the use of multi-scale approaches unavoidable. Further, changes in the atomic structure of material surfaces that can lead to surface reconstruction, and in the structure of proteins that can result in complete denaturation of the adsorbed molecules, can create many intermediate structural and energetic states that complicate sampling. In this review, we address the challenges posed to theoretical and computational methods in achieving accurate descriptions of the physical, chemical and mechanical properties of protein-surface systems. In this context, we discuss the applicability of different modeling and simulation techniques ranging from quantum mechanics through all-atom molecular mechanics to coarse-grained approaches. We examine uses of different sampling methods, as well as free energy calculations. Furthermore, we review computational studies of protein-surface interactions and discuss the successes and limitations of current approaches.

Mechanisms of Nickel Toxicity in the Highly Sensitive Embryos of the Sea Urchin Evechinus chloroticus, and the Modifying Effects of Natural Organic Matter

A 96 h toxicity test showed that the embryos of the New Zealand sea urchin (Evechinus chloroticus) are the most sensitive of all studied marine species to waterborne nickel (Ni), with the EC50 for the development of fully formed pluteus larvae found to be 14 μg L(-1). Failure to develop a standard larval shape suggested skeletal impairment. Whole body ions (Na, Mg) increased with Ni exposure and calcium influx was depressed. The effects of natural organic matter (NOM) on Ni accumulation and toxicity were also examined in three different seawater sources (nearshore, offshore, and near the outlet of a "brown water" stream). At low dissolved organic carbon (DOC) concentrations the brown water NOM was protective against Ni toxicity, however at higher DOC concentrations it exacerbated developmental toxicity in the presence of Ni. These results show that sea urchin development is highly sensitive to Ni via a mechanism that involves ionoregulatory disturbance, and that Ni toxicity is influenced by environmental factors such as NOM. These data will be critical for the development of water quality guidelines for Ni in the marine environment.

Sea Urchin Morphogenesis

In the sea urchin morphogenesis follows extensive molecular specification. The specification controls the many morphogenetic events and these, in turn, precede patterning steps that establish the larval body plan. To understand how the embryo is built it was necessary to understand those series of molecular steps. Here an example of the historical sequence of those discoveries is presented as it unfolded over the last 50 years, the years during which major progress in understanding development of many animals and plants was documented by CTDB. In sea urchin development a rich series of experimental studies first established many of the phenomenological components of skeletal morphogenesis and patterning without knowledge of the molecular components. The many discoveries of transcription factors, signals, and structural proteins that contribute to the shape of the endoskeleton of the sea urchin larva then followed as molecular tools became available. A number of transcription factors and signals were discovered that were necessary for specification, morphogenesis, and patterning. Perturbation of the transcription factors and signals provided the means for assembling models of the gene regulatory networks used for specification and controlled the subsequent morphogenetic events. The earlier experimental information informed perturbation experiments that asked how patterning worked. As a consequence it was learned that ectoderm provides a series of patterning signals to the skeletogenic cells and as a consequence the skeletogenic cells secrete a highly patterned skeleton based on their ability to genotypically decode the localized reception of several signals. We still do not understand the complexity of the signals received by the skeletogenic cells, nor do we understand in detail how the genotypic information shapes the secreted skeletal biomineral, but the current knowledge at least outlines the sequence of events and provides a useful template for future discoveries.

Cloning and identification of a YY-1 homolog as a potential transcription factor from Pinctada fucata

Biomineralization is an important and ubiquitous process in organisms. The shell formation of mollusks is a typical biomineral physical activity and is used as a canonical model in biomineralization research. Most recent studies focused on the identification of matrix proteins involved in shell formation; however, little is known about their transcriptional regulation mechanism, especially the transcription factors involved in shell formation. In this study, we identified a homolog of the YY-1 transcriptional factor from Pinctada fucata, named Pf-YY-1, and characterized its expression pattern and biological functions. Pf-YY-1 has a typical zinc finger motif highly similar to those in humans, mice, and other higher organisms, which indicated its DNA-binding capability and its function as a transcription factor. Pf-YY-1 is ubiquitously expressed in many tissues, but at a higher level in the mantle, which suggested a role in biomineralization. The expression pattern of Pf-YY-1 during pearl sac development was quite similar to, and was synchronized with, those of Prisilkin-39, ACCBP, and other genes involved in biomineralization, which also suggested its function in biomineralization.

microRNA-31 modulates skeletal patterning in the sea urchin embryo

MicroRNAs (miRNAs) are small non-coding RNAs that repress the translation and reduce the stability of target mRNAs in animal cells. microRNA-31 (miR-31) is known to play a role in cancer, bone formation and lymphatic development. However, studies to understand the function of miR-31 in embryogenesis have been limited. We examined the regulatory role of miR-31 in early development using the sea urchin as a model. miR-31 is expressed at all stages of development and its knockdown (KD) disrupts the patterning and function of primary mesenchyme cells (PMCs), which form the embryonic skeleton spicules. We identified that miR-31 directly represses Pmar1, Alx1, Snail and VegfR7 within the PMC gene regulatory network using reporter constructs. Further, blocking the miR-31-mediated repression of Alx1 and/or VegfR7 in the developing embryo resulted in defects in PMC patterning and skeletogenesis. The majority of the mislocalized PMCs in miR-31 KD embryos did not express VegfR10, indicating that miR-31 regulates VegfR gene expression within PMCs. In addition, miR-31 indirectly suppresses Vegf3 expression in the ectoderm. These results indicate that miR-31 coordinately suppresses genes within the PMCs and in the ectoderm to impact PMC patterning and skeletogenesis. This study identifies the novel function and molecular mechanism of miR-31-mediated regulation in the developing embryo.

H(+)/K(+) ATPase activity is required for biomineralization in sea urchin embryos

The bioelectrical signatures associated with regeneration, wound healing, development, and cancer are changes in the polarization state of the cell that persist over long durations, and are mediated by ion channel activity. To identify physiologically relevant bioelectrical changes that occur during normal development of the sea urchin Lytechinus variegatus, we tested a range of ion channel inhibitors, and thereby identified SCH28080, a chemical inhibitor of the H(+)/K(+) ATPase (HKA), as an inhibitor of skeletogenesis. In sea urchin embryos, the primary mesodermal lineage, the PMCs, produce biomineral in response to signals from the ectoderm. However, in SCH28080-treated embryos, aside from randomization of the left-right axis, the ectoderm is normally specified and differentiated, indicating that the block to skeletogenesis observed in SCH28080-treated embryos is PMC-specific. HKA inhibition did not interfere with PMC specification, and was sufficient to block continuing biomineralization when embryos were treated with SCH28080 after the initiation of skeletogenesis, indicating that HKA activity is continuously required during biomineralization. Ion concentrations and voltage potential were abnormal in the PMCs in SCH28080-treated embryos, suggesting that these bioelectrical abnormalities prevent biomineralization. Our results indicate that this effect is due to the inhibition of amorphous calcium carbonate precipitation within PMC vesicles.

Carbonic anhydrase inhibition blocks skeletogenesis and echinochrome production in Paracentrotus lividus and Heliocidaris tuberculata embryos and larvae

Carbonic anhydrases (CAs) are a family of widely distributed metalloenzymes, involved in diverse physiological processes. These enzymes catalyse the reversible conversion of carbon dioxide to protons and bicarbonate. At least 19 genes encoding for CAs have been identified in the sea urchin genome, with one of these localized to the skeletogenic mesoderm (primary mesenchyme cells, PMCs). We investigated the effects of a specific inhibitor of CA, acetazolamide (AZ), on development of two sea urchin species with contrasting investment in skeleton production, Paracentrotus lividus and Heliocidaris tuberculata, to determine the role of CA on PMC differentiation, skeletogenesis and on non-skeletogenic mesodermal (NSM) cells. Embryos were cultured in the presence of AZ from the blastula stage prior to skeleton formation and development to the larval stage was monitored. At the dose of 8 mmol/L AZ, 98% and 90% of P. lividus and H. tuberculata embryos lacked skeleton, respectively. Nevertheless, an almost normal PMC differentiation was indicated by the expression of msp130, a PMC-specific marker. Strikingly, the AZ-treated embryos also lacked the echinochrome pigment produced by the pigment cells, a subpopulation of NSM cells with immune activities within the larva. Conversely, all ectoderm and endoderm derivatives and other subpopulations of mesoderm developed normally. The inhibitory effects of AZ were completely reversed after removal of the inhibitor from the medium. Our data, together with new information concerning the involvement of CA on skeleton formation, provide evidence for the first time of a possible role of the CAs in larval immune pigment cells.

In vivo enrichment of magnesium ions modifies sea urchin spicule properties

Sea urchin embryos produce an endoskeleton composed of two symmetric spicules that consist of calcite, containing approximately 5% magnesium. The function of magnesium ions in mineral formation in vivo and the consequence of their incorporation into the mineral on mechanical properties are largely unknown. The authors investigated the in vivo effects of excess magnesium ion concentrations in the medium on skeletal development of Arbacia lixula. Morphological deformations of pluteus larval spicules were observed after cultivation in Mg2+-enriched sea water. Energy dispersive X-ray spectroscopy showed that magnesium ions were homogeneously distributed for complete larvae and spicule cross-sections. Magnesium ion content was quantified by inductively coupled plasma optical emission spectrometry, which revealed a considerable increased incorporation of magnesium ions into spicules of larvae from Mg2+-enriched sea water. However, no change in crystal polymorph formation was observed by X-ray diffraction. Mechanical properties of spicule cross-sections were analysed by nanoindentation and revealed significantly higher stiffness values for spicules from Mg2+-enriched sea water compared to the control, whereas no significant change in hardness values was obtained. This in vivo study shows that increased magnesium ion incorporation into sea urchin larval spicules modifies the mineral properties and supports this model to investigate the effect of minor ions on biomineralisation.

Spine and test skeletal matrices of the Mediterranean sea urchin Arbacia lixula--a comparative characterization of their sugar signature

Calcified structures of sea urchins are biocomposite materials that comprise a minor fraction of organic macromolecules, such as proteins, glycoproteins and polysaccharides. These macromolecules are thought to collectively regulate mineral deposition during the process of calcification. When occluded, they modify the properties of the mineral. In the present study, the organic matrices (both soluble and insoluble in acetic acid) of spines and tests from the Mediterranean black sea urchin Arbacia lixula were extracted and characterized, in order to determine whether they exhibit similar biochemical signatures. Bulk characterizations were performed by mono-dimensional SDS/PAGE, FT-IR spectroscopy, and an in vitro crystallization assay. We concentrated our efforts on characterization of the sugar moieties. To this end, we determined the monosaccharide content of the soluble and insoluble organic matrices of A. lixula spines and tests by HPAE-PAD, together with their respective lectin-binding profiles via enzyme-linked lectin assay. Finally, we performed in situ localization of N-acetyl glucosamine-containing saccharides on spines and tests using gold-conjugated wheatgerm agglutinin. Our data show that the test and spine matrices exhibit different biochemical signatures with regard to their saccharidic fraction, suggesting that future studies should analyse the regulation of mineral deposition by the matrix in these two mineralized structures in detail. This study re-emphasizes the importance of non-protein moieties, i.e. sugars, in calcium carbonate systems, and highlights the need to clearly identify their function in the biomineralization process.

Intracrystalline inclusions within single crystalline hosts: from biomineralization to bio-inspired crystal growth

A review of the inclusion of organic matter within single crystalline hosts: from biogenic minerals to bio-inspired nanohybrid single crystal composites.

Exposure of Paracentrotus lividus male gametes to engineered nanoparticles affects skeletal bio-mineralization processes and larval plasticity

The aim of this study is to contribute to the understanding of the mechanisms underlying nanoparticle (NP)-induced embryotoxicity in aquatic organisms. We previously demonstrated that exposure of male gametes to NPs causes non-dose-dependent skeletal damage in sea urchin (Paracentrotus lividus) larvae. In the present study, the molecular mechanisms responsible for these anomalies in sea urchin development from male gametes exposed to cobalt (Co), titanium dioxide (TiO2) and silver (Ag) NPs were investigated by histochemical, immunohistochemical and Western blot analyses. P. lividus sperm were exposed to different NP concentrations (from 0.0001 to 1 mg/L). The distribution of molecules related to skeletogenic cell identification, including ID5 immunoreactivity (IR), wheat germ agglutinin (WGA) affinity and fibronectin (FN) IR, were investigated by confocal laser scanning microscopy at the gastrula (24 h) and pluteus (72 h) stages. Our results identified a spatial correspondence among PMCs, ID5 IR and WGA affinity sites. The altered FN pattern suggests that it is responsible for the altered skeletogenic cell migration, while the Golgi apparatus of the skeletogenic cells, denoted by their WGA affinity, shows different aspects according to the degree of anomalies caused by NP concentrations. The ID5 IR, a specific marker of skeletogenic cells in sea urchin embryos (in particular of the msp130 protein responsible for Ca(2+) and Mg(2+) mineralization), localized in the cellular strands prefiguring the skeletal rods in the gastrula stage and, in the pluteus stage, was visible according to the degree of mineralization of the skeleton. In conclusion, the present study suggests that the investigated NPs suspended in seawater interfere with the bio-mineralization processes in marine organisms, and the results of this study offer a new series of specific endpoints for the mechanistic understanding of NP toxicity.

The effects of copper and nickel on the embryonic life stages of the purple sea urchin (Strongylocentrotus purpuratus)

The aim of this research was to generate data on the mechanisms of toxicity of copper [Cu (4-12 µg/L)] and nickel [Ni (33-40 µg/L)] during continuous sublethal exposure in seawater (32 ppt, 15 °C) in a sensitive test organism (Strongylocentrotus purpuratus) at its most sensitive life stage (developing embryo). Whole-body ions [calcium (Ca), sodium (Na), potassium (K), and magnesium (Mg)], metal burdens, Ca uptake, and Ca ATPase activity were measured every 12 h during the first 72-84 h of development. Ionoregulatory disruption was clearly an important mechanism of toxicity for both metals and occurred with minimal metal bioaccumulation. Most noteworthy was a significant disruption of Ca homeostasis, which was evident from an inhibition of unidirectional Ca uptake rates, whole-body Ca accumulation, and Ca ATPase activity intermittently during 72-84 h of development. At various times, Cu- and Ni-exposed embryos also displayed lower levels of K and increased levels of Na suggesting inhibition of Na/K ATPase activity. Greater levels of Mg during initial stages of development in Cu-exposed embryos were also observed and were considered a possible compensatory mechanism for disruptions to Ca homeostasis because both of these ions are important constituents of the developing spicule. Notably, most of these effects occurred during the initial stages of development but were reversed by 72-84 h. We therefore propose that it is of value to study the toxic impacts of contaminants periodically during development before the traditional end point of 48-72 h.

Lectin uptake and incorporation into the calcitic spicule of sea urchin embryos

Primary mesenchyme cells (PMCs) are skeletogenenic cells that produce a calcareous endoskeleton in developing sea urchin larvae. The PMCs fuse to form a cavity in which spicule matrix proteins and calcium are secreted forming the mineralized spicule. In this study, living sea urchin embryos were stained with fluorescently conjugated wheat germ agglutinin, a lectin that preferentially binds to PMCs, and the redistribution of this fluorescent tag was examined during sea urchin development. Initially, fluorescence was associated primarily with the surface of PMCs. Subsequently, the fluorescent label redistributed to intracellular vesicles in the PMCs. As the larval skeleton developed, intracellular granular staining diminished and fluorescence appeared in the spicules. Spicules that were cleaned to remove membranous material associated with the surface exhibited bright fluorescence, which indicated that fluorescently labelled lectin had been incorporated into the spicule matrix. The results provide evidence for a cellular pathway in which material is taken up at the cell surface, sequestered in intracellular vesicles and then incorporated into the developing spicule.

Sublethal mechanisms of Pb and Zn toxicity to the purple sea urchin (Strongylocentrotus purpuratus) during early development

In order to understand sublethal mechanisms of lead (Pb) and zinc (Zn) toxicity, developing sea urchins were exposed continuously from 3h post-fertilization (eggs) to 96 h (pluteus larvae) to 55 (±2.4) μgPb/L or 117 (±11)μgZn/L, representing ~ 70% of the EC50 for normal 72 h development. Growth, unidirectional Ca uptake rates, whole body ion concentrations (Na, K, Ca, Mg), Ca(2+) ATPase activity, and metal bioaccumulation were monitored every 12h over this period. Pb exhibited marked bioaccumulation whereas Zn was well-regulated, and both metals had little effect on growth, measured as larval dry weight, or on Na, K, or Mg concentrations. Unidirectional Ca uptake rates (measured by (45)Ca incorporation) were severely inhibited by both metals, resulting in lower levels of whole body Ca accumulation. The greatest disruption occurred at gastrulation. Ca(2+) ATPase activity was also significantly inhibited by Zn but not by Pb. Interestingly, embryos exposed to Pb showed some capacity for recovery, as Ca(2+)ATPase activities increased, Ca uptake rates returned to normal intermittently, and whole body Ca levels were restored to control values by 72-96 h of development. This did not occur with Zn exposure. Both Pb and Zn rendered their toxic effects through disruption of Ca homeostasis, though likely through different proximate mechanisms. We recommend studying the toxicity of these contaminants periodically throughout development as an effective way to detect sublethal effects, which may not be displayed at the traditional toxicity test endpoint of 72 h.

Biogenic and synthetic high magnesium calcite - a review

Systematic studies on the Mg distributions, the crystal orientations, the formation mechanisms and the mechanical properties of biogenic high-Mg calcites in different marine organisms were summarized in detail in this review. The high-Mg calcites in the hard tissues of marine organisms mentioned generally own a few common features as follows. Firstly, the Mg distribution is not uniform in most of the minerals. Secondly, high-Mg calcite biominerals are usually composed of nanoparticles that own almost the same crystallographic orientations and thus they behave like single crystals or mesocrystals. Thirdly, the formation of thermodynamically unstable high-Mg calcites in marine organisms under mild conditions is affected by three key factors, that is, the formation of amorphous calcium (magnesium) carbonate precursor, the control of polymorph via biomolecules and the high Mg/Ca ratios in modern sea. Lastly, the existence of Mg ions in the Mg-containing calcite may improve the mechanical properties of biogenic minerals. Furthermore, the key progress in the synthesis of high-Mg calcites in the laboratory based on the formation mechanisms of the biogenic high-Mg calcites was reviewed. Many researchers have realized the synthesis of high-Mg calcites in the laboratory under ambient conditions with the help of intermediate amorphous phase, mixed solvents, organic/inorganic surfaces and soluble additives. Studies on the structural analysis and formation mechanisms of thermodynamically unstable biogenic high-Mg calcite minerals may shed light on the preparation of functional materials with enhanced mechanical properties.

Developmental abnormalities and changes in cholinesterase activity in sea urchin embryos and larvae from sperm exposed to engineered nanoparticles

The objective of this study is to examine the toxicity of engineered nanoparticles (NPs) that are dispersed in sea water by using an in vivo model. Because many products of nanotechnology contain NPs and are commonly used and well-established in the market, the accidental release of NPs into the air and water is quite possible. Indeed, at the end of their life cycle, some NPs are inevitably released into waste water and can reach marine ecosystem and affect the organisms there. Although there are few data on the presence of NPs in the marine environment, our awareness of their potential impact on environmental and organismal health is growing. Shallow-water benthonic organisms such as sea urchins provide planktonic larvae as a trophic base for finfish juveniles and are exposed to water from estuaries and precipitation. Such organisms can therefore be directly affected by NPs that are dispersed into those media. We evaluated the effects of exposure to different concentrations of nanosilver, titanium oxide and cobalt NPs on the sperm of the sea urchin Paracentrotus lividus by analyzing the functionality and the morphology and biochemistry of the first developmental stages of the sea urchin. Sperm were exposed to sea water containing suspensions of NPs ranging from 0.0001 mg/L to 1 mg/L. Fertilization ability was not affected, but developmental anomalies were identified in embryos from the gastrula to pluteus stages, including morphological alterations of the skeletal rods. In addition, the enzymatic activity (cholinesterase, ChE) of the larvae was measured. Acetylcholinesterase (AChE) and propionylcholinesterase activity (PrChE) was affected in all of the exposed samples. The results did not vary consistently with the concentration of NP, but controls were significantly different from exposed samples. Exposure of sea urchin to these NPs may cause neurotoxic damage, and the altered ChE activity may be involved in skeletogenic aberrations. In conclusion, the sea urchin represents a suitable and sensitive model for testing the toxicity and effects of engineered NPs that are dispersed in sea water.

Temperature and CO(2) additively regulate physiology, morphology and genomic responses of larval sea urchins, Strongylocentrotus purpuratus

Ocean warming and ocean acidification, both consequences of anthropogenic production of CO2, will combine to influence the physiological performance of many species in the marine environment. In this study, we used an integrative approach to forecast the impact of future ocean conditions on larval purple sea urchins (Strongylocentrotus purpuratus) from the northeast Pacific Ocean. In laboratory experiments that simulated ocean warming and ocean acidification, we examined larval development, skeletal growth, metabolism and patterns of gene expression using an orthogonal comparison of two temperature (13°C and 18°C) and pCO2 (400 and 1100 μatm) conditions. Simultaneous exposure to increased temperature and pCO2 significantly reduced larval metabolism and triggered a widespread downregulation of histone encoding genes. pCO2 but not temperature impaired skeletal growth and reduced the expression of a major spicule matrix protein, suggesting that skeletal growth will not be further inhibited by ocean warming. Importantly, shifts in skeletal growth were not associated with developmental delay. Collectively, our results indicate that global change variables will have additive effects that exceed thresholds for optimized physiological performance in this keystone marine species.

Low Mg/Ca ratio alters material properties in sea urchin larvae skeleton

Biomineralization in organisms is strictly regulated, and therefore, chemical compositions as well as crystal structures of the minerals are species specific. During the embryonic development, sea urchin larvae produce a calcite endoskeleton (spicules) that contains about 5% of Mg. For sea urchins and other organisms, it is assumed that Mg is important for the process of biomineralization and for the mechanical properties of the resulting biomineral. To study the influence of Mg on skeletal growth and on biomineral structure and composition, sea urchin larvae spicules were chosen as an in vivo test system. For this purpose, the Mg/Ca ratio was modified in the artificial seawater medium wherein sea urchin larvae were growing. It was shown that Mg deficiency during larval development caused morphology defects of the larvae and of their calcite spicules. The Mg distribution within the larvae skeleton was analyzed and found to be homogenous. An in vivo reduction of the Mg content influenced the mechanical performance of larval spicules (Young’s modulus and hardness). The investigations of larvae exposed to reduced Mg conditions highlight the important role Mg plays for sea urchin larvae development, biomineralization process and the resulting biomineral. The sea urchin larvae are presented as an ideal model to study different effects on larval development and morphology, especially on the biomineral properties.

Effects of the neurotoxic thionophosphate pesticide chlorpyrifos on differentiating alternative models

Studies by researchers worldwide have revealed that, even in industrialised nations, people, infants and the aged in particular, are even more exposed to neurotoxic drugs as a consequence of the increased quantity of pesticide residues in food. This phenomenon, as underlined by The Worldwatch Institute (2006), is linked to the exponential increase in the use of these toxic compounds over the last 40 years, up from 0.49 kg per hectare in 1961 to 2 kg in 2004, with the result that these substances are found in the daily diet. Many studies have demonstrated how the assumption of pesticides in the neonatal period and early infancy can alter the development and function of the nervous, immune, endocrine and reproductive apparatuses. Moreover, the unequivocal relationship between brain tumours, infant leukemia and pesticides are well recognised. On the basis of the above information, the effects of the neurotoxic thionophosphate pesticide chlorpyrifos (CPF) have been tested, considering biomarkers of toxicity and toxicity endpoint, on the biological models Dictyostelium discoideum, Paracentrotus lividus, and NTera2 Cells, as they are compatible with the 3Rs strategy (Reduction, Replacement, and Refinement in animal experiments). Our results have revealed that developing organisms are particularly sensitive to the toxic effects of CPF.

Transcriptomic responses to ocean acidification in larval sea urchins from a naturally variable pH environment

Some marine ecosystems already experience natural declines in pH approximating those predicted with future anthropogenic ocean acidification (OA), the decline in seawater pH caused by the absorption of atmospheric CO2 . The molecular mechanisms that allow organisms to inhabit these low pH environments, particularly those building calcium carbonate skeletons, are unknown. Also uncertain is whether an enhanced capacity to cope with present day pH variation will confer resistance to future OA. To address these issues, we monitored natural pH dynamics within an intertidal habitat in the Northeast Pacific, demonstrating that upwelling exposes resident species to pH regimes not predicted to occur elsewhere until 2100. Next, we cultured the progeny of adult purple sea urchins (Strongylocentrotus purpuratus) collected from this region in CO2 -acidified seawater representing present day and near future ocean scenarios and monitored gene expression using transcriptomics. We hypothesized that persistent exposure to upwelling during evolutionary history will have selected for increased pH tolerance in this population and that their transcriptomic response to low pH seawater would provide insight into mechanisms underlying pH tolerance in a calcifying species. Resulting expression patterns revealed two important trends. Firstly, S. purpuratus larvae may alter the bioavailability of calcium and adjust skeletogenic pathways to sustain calcification in a low pH ocean. Secondly, larvae use different strategies for coping with different magnitudes of pH stress: initiating a robust transcriptional response to present day pH regimes but a muted response to near future conditions. Thus, an enhanced capacity to cope with present day pH variation may not translate into success in future oceans.

ISWI contributes to ArsI insulator function in development of the sea urchin

Insulators are genomic elements that regulate transcriptional activity by forming chromatin boundaries. Various DNA insulators have been identified or are postulated in many organisms, and the paradigmatic CTCF-dependent insulators are perhaps the best understood and most widespread in function. The diversity of DNA insulators is, however, understudied, especially in the context of embryonic development, when many new gene territories undergo transitions in functionality. Here we report the functional analysis of the arylsulfatase insulator (ArsI) derived from the sea urchin, which has conserved insulator activity throughout the many metazoans tested, but for which the molecular mechanism of function is unknown. Using a rapid in vivo assay system and a high-throughput mega-shift assay, we identified a minimal region in ArsI that is responsible for its insulator function. We discovered a small set of proteins specifically bound to the minimal ArsI region, including ISWI, a known chromatin-remodeling protein. During embryogenesis, ISWI was found to interact with select ArsI sites throughout the genome, and when inactivated led to misregulation of select gene expression, loss of insulator activity and aberrant morphogenesis. These studies reveal a mechanistic basis for ArsI function in the gene regulatory network of early development.

The multiple effects of amino acids on the early stages of calcium carbonate crystallization

Proteins have found their way into many of Nature’s structures due to their structural stability, diversity in function and composition, and ability to be regulated as well as be regulators themselves. In this study, we investigate the constitutive amino acids that make up some of these proteins which are involved in CaCO3 mineralization – either in nucleation, crystal growth, or inhibition processes. By assaying all 20 amino acids with vapor diffusion and in situ potentiometric titration, we have found specific amino acids having multiple effects on the early stages of CaCO3 crystallization. These same amino acids have been independently implicated as constituents in liquid-like precursors that form mineralized tissues, processes believed to be key effects of biomineralization proteins in several biological model systems.

Phase transitions in biogenic amorphous calcium carbonate

Crystalline biominerals do not resemble faceted crystals. Current explanations for this property involve formation via amorphous phases. Using X-ray absorption near-edge structure (XANES) spectroscopy and photoelectron emission microscopy (PEEM), here we examine forming spicules in embryos of Strongylocentrotus purpuratus sea urchins, and observe a sequence of three mineral phases: hydrated amorphous calcium carbonate (ACC · H(2)O) → dehydrated amorphous calcium carbonate (ACC) → calcite. Unexpectedly, we find ACC · H(2)O-rich nanoparticles that persist after the surrounding mineral has dehydrated and crystallized. Protein matrix components occluded within the mineral must inhibit ACC · H(2)O dehydration. We devised an in vitro, also using XANES-PEEM, assay to identify spicule proteins that may play a role in stabilizing various mineral phases, and found that the most abundant occluded matrix protein in the sea urchin spicules, SM50, stabilizes ACC · H(2)O in vitro.

Structure-property relationships of a biological mesocrystal in the adult sea urchin spine

Structuring over many length scales is a design strategy widely used in Nature to create materials with unique functional properties. We here present a comprehensive analysis of an adult sea urchin spine, and in revealing a complex, hierarchical structure, show how Nature fabricates a material which diffracts as a single crystal of calcite and yet fractures as a glassy material. Each spine comprises a highly oriented array of Mg-calcite nanocrystals in which amorphous regions and macromolecules are embedded. It is postulated that this mesocrystalline structure forms via the crystallization of a dense array of amorphous calcium carbonate (ACC) precursor particles. A residual surface layer of ACC and/or macromolecules remains around the nanoparticle units which creates the mesocrystal structure and contributes to the conchoidal fracture behavior. Nature's demonstration of how crystallization of an amorphous precursor phase can create a crystalline material with remarkable properties therefore provides inspiration for a novel approach to the design and synthesis of synthetic composite materials.

Expression pattern of polyketide synthase-2 during sea urchin development

Polyketide synthases (PKSs) are a large group of proteins responsible for the biosynthesis of polyketide compounds, which are mainly found in bacteria, fungi, and plants. Polyketides have a wide array of biological functions, including antibiotic, antifungal, predator defense, and light responses. In this study, we describe the developmental expression pattern of pks2, one of two pks found in the sea urchin genome. Throughout development, pks2 expression was restricted to skeletogenic cells and their precursors. Pks2 was first detected during the blastula stage. The transcript level peaked at hatched blastula, when all skeletogenic cell precursors expressed pks2. This was followed by a steady decline in expression in the skeletogenic cells on the aboral side of the embryo. By the prism stage, pks2 expression was limited to only 3-4 skeletogenic cells localized on the oral side.

CO2 induced seawater acidification impacts sea urchin larval development II: gene expression patterns in pluteus larvae

Extensive use of fossil fuels is leading to increasing CO(2) concentrations in the atmosphere and causes changes in the carbonate chemistry of the oceans which represents a major sink for anthropogenic CO(2). As a result, the oceans' surface pH is expected to decrease by ca. 0.4 units by the year 2100, a major change with potentially negative consequences for some marine species. Because of their carbonate skeleton, sea urchins and their larval stages are regarded as likely to be one of the more sensitive taxa. In order to investigate sensitivity of pre-feeding (2 days post-fertilization) and feeding (4 and 7 days post-fertilization) pluteus larvae, we raised Strongylocentrotus purpuratus embryos in control (pH 8.1 and pCO(2) 41 Pa e.g. 399 μatm) and CO(2) acidified seawater with pH of 7.7 (pCO(2) 134 Pa e.g. 1318 μatm) and investigated growth, calcification and survival. At three time points (day 2, day 4 and day 7 post-fertilization), we measured the expression of 26 representative genes important for metabolism, calcification and ion regulation using RT-qPCR. After one week of development, we observed a significant difference in growth. Maximum differences in size were detected at day 4 (ca. 10% reduction in body length). A comparison of gene expression patterns using PCA and ANOSIM clearly distinguished between the different age groups (two-way ANOSIM: Global R=1) while acidification effects were less pronounced (Global R=0.518). Significant differences in gene expression patterns (ANOSIM R=0.938, SIMPER: 4.3% difference) were also detected at day 4 leading to the hypothesis that differences between CO(2) treatments could reflect patterns of expression seen in control experiments of a younger larva and thus a developmental artifact rather than a direct CO(2) effect. We found an up regulation of metabolic genes (between 10%and 20% in ATP-synthase, citrate synthase, pyruvate kinase and thiolase at day 4) and down regulation of calcification related genes (between 23% and 36% in msp130, SM30B, and SM50 at day 4). Ion regulation was mainly impacted by up regulation of Na(+)/K(+)-ATPase at day 4 (15%) and down regulation of NHE3 at day 4 (45%). We conclude that in studies in which a stressor induces an alteration in the speed of development, it is crucial to employ experimental designs with a high time resolution in order to correct for developmental artifacts. This helps prevent misinterpretation of stressor effects on organism physiology.

Biomineral nanoparticles are space-filling

Sea urchin biominerals have been shown to form from aggregating nanoparticles of amorphous calcium carbonate (ACC), which then crystallize into macroscopic single crystals of calcite. Here we measure the surface areas of these biominerals and find them to be comparable to those of space-filling macroscopic geologic calcite crystals. These biominerals differ from synthetic mesocrystals, which are invariably porous. We propose that space-filling ACC is the structural precursor for echinoderm biominerals.

Laser Light Scattering Observations of Liquid–Liquid Phase Separation in a Polymer-Induced Liquid-Precursor (PILP) Mineralization Process

A Polymer-Induced Liquid-Precursor (PILP) process for mineralization of calcium carbonate has been studied in-situ by laser light scattering. Static and dynamic light scattering data were obtained from CaCl2 solutions containing poly(aspartic acid). Under these conditions calcium carbonate mineralizes through a liquid droplet precursor phase when the solution is exposed to the decomposition products of ammonium carbonate. Our measurements probe the integrated scatterer mass and the apparent hydrodynamic radius Rh,app of the droplets as they nucleate and coalesce. The data reveal three stages in the formation of the PILP phase: an early stage of droplet growth to Rh,app ≈ 250 nm; a mid-time stage of fluctuations and polydispersity in particle size; and a final growth period where Rh,app increases from 350 nm to the micron scale. Aggregation of precursor droplets, rather than atom-by-atom growth, is the dominant mechanism of mineral formation under these conditions. With respect to biomineralization, this first observation of 100-nm-scale droplets is significant, implying a possibility to mineralize from the liquid phase within the nanoscale compartments in which many biominerals form.