Expression of univin, a TGF-β growth factor, requires ectoderm–ECM interaction and promotes skeletal growth in the sea urchin embryo

Carbonic anhydrases in development: morphological observations and gene expression profiling in sea urchin embryos exposed to acetazolamide

Carbonic anhydrases (CANs) are conserved metalloenzymes catalysing the reversible hydration of carbon dioxide into protons and bicarbonate, with important roles in cells physiology. Some CAN-coding genes were found in sea urchin genome, although only one involved in embryonic skeletogenesis was described in Paracentrotus lividus. Here, we investigated gene expression patterns of P. lividus embryos cultured in the presence of acetazolamide (AZ), a CAN inhibitor, to combine morphological defects with their molecular underpinning. CAN inhibition blocked skeletogenesis, affected the spatial/temporal expression of some biomineralization-related genes, inhibited embryos swimming. A comparative analysis on the expression of 127 genes in control and 3 h/24 h AZ-treated embryos, using NanoString technology, showed the differential expression of genes encoding for structural/regulatory proteins, with different embryonic roles: biomineralization, transcriptional regulation, signalling, development and defence response. The study of the differentially expressed genes and the signalling pathways affected, besides in silico analyses and a speculative 'interactomic model', leads to predicting the presence of various CAN isoforms, possibly involved in different physiological processes/activities in sea urchin embryo, and their potential target genes/proteins. Our findings provide new valuable molecular data for further studies in several biological fields: developmental biology (biomineralization, axes patterning), cell differentiation (neural development) and drug toxicology (AZ effects on embryos/tissues).

Gene Expression Analysis of the Stress Response to Lithium, Nickel, and Zinc in Paracentrotus lividus Embryos

Many anthropogenic pollutants such as metals are discharged into the marine environment through modern sources. Among these, lithium (Li), nickel (Ni), and zinc (Zn) can interfere with biological processes in many organisms when their concentration rises. These metals are toxic to sea urchin embryos, affecting their development. Indeed, animal/vegetal and dorso/ventral embryonic axes are differently perturbed: Li is a vegetalizing agent, Ni can disrupt dorso-ventral axis, Zn can be animalizing. To address the molecular response adopted by embryos to cope with these metals or involved in the gene networks regulating embryogenesis, and to detect new biomarkers for evaluating hazards in polluted environments in a well-known in vivo model, we applied a high-throughput screening approach to sea urchin embryos. After fertilization, Paracentrotus lividus embryos were exposed to Li, Ni, and Zn for 24/48 h. At both endpoints, RNAs were analyzed by NanoString nCounter technology. By in silico analyses, we selected a panel of 127 transcripts encoding for regulatory and structural proteins, ranked in categories: Apoptosis, Defense, Immune, Nervous, Development, and Biomineralization. The data analysis highlighted the dysregulation of many genes in a metal-dependent manner. A functional annotation analysis was performed by the KEEG Orthology database. This study provides a platform for research on metals biomarkers in sea urchins.

Development of a larval nervous system in the sea urchin

This review reports recent findings on the specification and patterning of neurons that establish the larval nervous system of the sea urchin embryo. Neurons originate in three regions of the embryo. Perturbation analyses enabled construction of gene regulatory networks controlling the several neural cell types. Many of the mechanisms described reflect shared features of all metazoans and others are conserved among deuterostomes. This nervous system with a very small number of neurons supports the feeding and swimming behaviors of the larva until metamorphosis when an adult nervous system replaces that system.

Identification and localization of growth factor genes in the sea cucumber, Holothuria scabra

The sea cucumber Holothuria scabra is both an economically important species in Asian countries and an emerging experimental model for research studies in regeneration and medicinal bioactives. Growth factors and their receptors are known to be key components that guide tissue repair and renewal, yet validation of their presence in H. scabra has not been established. We performed a targeted in silico search of H. scabra transcriptome data to elucidate conserved growth factor family and receptor genes. In total, 42 transcripts were identified, of which 9 were validated by gene cloning and sequencing. The H. scabra growth factor genes, such as bone morphogenetic protein 2A (BMP 2A), bone morphogenetic protein 5-like (BMP5-like), neurotrophin (NT) and fibroblast growth factor 18 (FGF18), were selected for further analyses, including phylogenetic comparison and spatial gene expression using RT-PCR and in situ hybridization. Expression of all genes investigated were widespread in multiple tissues. However, BMP 2A, BMP5-like and NT were found extensively in the radial nerve cord cells, while FGF18 was highly expressed in connective tissue layer of the body wall. Our identification and expression analysis of the H. scabra growth factor genes provided the molecular information of growth factors in this species which may ultimately complement the research in regenerative medicine.

PI3K inhibition highlights new molecular interactions involved in the skeletogenesis of Paracentrotus lividus embryos

The sea urchin embryo develops a well-defined biomineralized endoskeleton, synthesized exclusively by the skeletogenic cells, supported by ectodermal cues for the correct skeleton patterning. The biomineralization process is tightly regulated via a hierarchical order of gene expression, including transcription and growth factors, biomineralization proteins. Recently, the role of kinases and intracellular signaling pathways in sea urchin skeletogenesis has been addressed, although the downstream components still remain unknown. In this study, we investigated the role of phosphatidylinositide 3-kinase (PI3K)-mediated signaling pathway in Paracentrotus lividus, to identify its genes/proteins targets. The effects of LY294002 (LY), a PI3K-specific inhibitor, were evaluated at morphological and molecular levels. Treatment with 40 μM LY from the blastula stage completely blocked skeleton deposition, which was reversed by wash out experiments. Besides, LY caused a slight delay in the tripartite gut development. Despite the skeleton absence, a few skeleton-specific proteins/mRNAs were regularly expressed and localized in LY-treated embryos, as shown for MSP130 and SM50 by immunofluorescence and in situ hybridization experiments. QPCR analyses showed that LY differently affected the expression of genes coding for other biomineralization proteins, transcription and growth factors. SM30 and carbonic anhydrase expression was severely downregulated, while almost all the transcription factors analyzed were upregulated. Based on the present results and in silico analyses, we propose an "interactomic" model simulating PI3K connections in P. lividus embryos. Our findings define a novel regulatory step in the embryonic skeletogenesis, and provide valuable molecular data for further studies on the role of PI3K signaling in invertebrate biomineralization.

The Impact of Chronic Heat Stress on the Growth, Survival, Feeding, and Differential Gene Expression in the Sea Urchin Strongylocentrotus intermedius

To explore the impact of chronic heat stress on commercial echinoderms, the present study assessed the effects of chronic high temperature on the growth, survival, feeding, and differential gene expression in the sea urchin Strongylocentrotus intermedius cultured in northern Yellow Sea in China. One suitable seawater condition (20°C) and one laboratory-controlled high temperature condition (25°C) were set up. After 28 days incubation, our results showed that: (1) The specific growth, survival, and ingestion rates of S. intermedius reared under high temperature (25°C) decreased compared to those reared under optimal temperature (20°C) conditions; (2) comparative transcriptome analysis identified 2,125 differentially expressed genes (DEGs) in S. intermedius reared under high temperature (25°C) compared to those subjected to optimal temperature condition (20°C), which included 1,015 upregulated and 1,100 downregulated genes. The accuracy of the transcriptome profiles was verified by quantitative real-time PCR (qRT-PCR). Further Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways analyses revealed that these DEGs mainly enriched the functional categories of ribosome, protein processing in endoplasmic reticulum, and prion diseases. A total of 732 temperature-induced expressed genes, such as ATP5, heat shock protein 70, and heat shock protein 90, were identified as candidates that were closely correlated with heat resistance in S. intermedius. Differentially expressed transcription factors (TFs), such as AP-1, Fos, CREB, and ZNF, were also identified as potential regulators that regulate the molecular network that was associated with responses to heat stress in sea urchins. Observations in the present study provide additional information that improves our understanding of the molecular mechanism of temperate echinoid species in response to heat stress, as well as theoretical basis for the molecular-assisted breeding of heat-resistant sea urchins.

Expression of exogenous mRNAs to study gene function in echinoderm embryos

With the completion of the genome sequencing projects, a new challenge for developmental biologists is to assign a function to the thousands of genes identified. Expression of exogenous mRNAs is a powerful, versatile and rapid technique that can be used to study gene function during development of the sea urchin. This chapter describes how this technique can be used to analyze gene function in echinoderm embryos, how it can be combined with cell transplantation to perform mosaic analysis and how it can be applied to identify downstream targets genes of transcription factors and signaling pathways. We describe specific examples of the use of overexpression of mRNA to analyze gene function, mention the benefits and current limitations of the technique and emphasize the importance of using different controls to assess the specificity of the effects observed. Finally, this chapter details the different steps, vectors and protocols for in vitro production of mRNA and phenotypic analysis.

Amino-modified polystyrene nanoparticles affect signalling pathways of the sea urchin (Paracentrotus lividus) embryos

Polystyrene nanoparticles have been shown to pose serious risk to marine organisms including sea urchin embryos based on their surface properties and consequently behaviour in natural sea water. The aim of this study is to investigate the toxicity pathways of amino polystyrene nanoparticles (PS-NH₂, 50 nm) in Paracentrotus lividus embryos in terms of development and signalling at both protein and gene levels. Two sub-lethal concentrations of 3 and 4 μg/mL of PS-NH₂ were used to expose sea urchin embryos in natural sea water (PS-NH₂ as aggregates of 143 ± 5 nm). At 24 and 48 h post-fertilisation (hpf) embryonic development was monitored and variations in the levels of key proteins involved in stress response and development (Hsp70, Hsp60, MnSOD, Phospho-p38 Mapk) as well as the modulation of target genes (Pl-Hsp70, Pl-Hsp60, Pl-Cytochrome b, Pl-p38 Mapk, Pl-Caspase 8, Pl-Univin) were measured. At 48 hpf various striking teratogenic effects were observed such as the occurrence of cells/masses randomly distributed, severe skeletal defects and delayed development. At 24 hpf a significant up-regulation of Pl-Hsp70, Pl-p38 Mapk, Pl-Univin and Pl-Cas8 genes was found, while at 48 hpf only for Pl-Univin was observed. Protein profile showed different patterns as a significant increase of Hsp70 and Hsp60 only after 48 hpf compared to controls. Conversely, P-p38 Mapk protein significantly increased at 24 hpf and decreased at 48 hpf. Our findings highlight that PS-NH₂ are able to disrupt sea urchin embryos development by modulating protein and gene profile providing new understandings into the signalling pathways involved.

TGF-β sensu stricto signaling regulates skeletal morphogenesis in the sea urchin embryo

Cell-cell signaling plays a prominent role in the formation of the embryonic skeleton of sea urchins, but the mechanisms are poorly understood. In the present study, we uncover an essential role for TGF-β sensu stricto signaling in this process. We show that TgfbrtII, a type II receptor dedicated to signaling through TGF-β sensu stricto, is expressed selectively in skeletogenic primary mesenchyme cells (PMCs) during skeleton formation. Morpholino (MO) knockdowns and studies with a specific TgfbrtII inhibitor (ITD-1) in both S. purpuratus and Lytechinus variegatus embryos show that this receptor is required for biomineral deposition. We provide pharmacological evidence that Alk4/5/7 is the cognate TGF-β type I receptor that pairs with TgfbrtII and show by inhibitor treatments of isolated micromeres cultured in vitro that both Alk4/5/7 and TgfbrtII function cell-autonomously in PMCs. Gene expression and gene knockdown studies suggest that TGF-β sensu stricto may be the ligand that interacts with TgfbrtII and support the view that this TGF-β superfamily ligand provides an essential, permissive cue for skeletogenesis, although it is unlikely to provide spatial patterning information. Taken together, our findings reveal that this model morphogenetic process involves an even more diverse suite of cell signaling pathways than previously appreciated and show that PMCs integrate a complex set of both generalized and spatially localized cues in assembling the endoskeleton.

First Morphological and Molecular Evidence of the Negative Impact of Diatom-Derived Hydroxyacids on the Sea Urchin Paracentrotus lividus

Oxylipins (including polyunsaturated aldehydes [PUAs], hydoxyacids, and epoxyalcohols) are the end-products of a lipoxygenase/hydroperoxide lyase metabolic pathway in diatoms. To date, very little information is available on oxylipins other than PUAs, even though they represent the most common oxylipins produced by diatoms. Here, we report, for the first time, on the effects of 2 hydroxyacids, 5- and 15-HEPE, which have never been tested before, using the sea urchin Paracentrotus lividus as a model organism. We show that HEPEs do induce developmental malformations but at concentrations higher when compared with PUAs. Interestingly, HEPEs also induced a marked developmental delay in sea urchin embryos, which has not hitherto been reported for PUAs. Recovery experiments revealed that embryos do not recover following treatment with HEPEs. Finally, we report the expression levels of 35 genes (involved in stress, development, differentiation, skeletogenesis, and detoxification processes) to identify the molecular targets affected by HEPEs. We show that the 2 HEPEs have very few common molecular targets, specifically affecting different classes of genes and at different times of development. In particular, 15-HEPE switched on fewer genes than 5-HEPE, upregulating mainly stress-related genes at a later pluteus stage of development. 5-HEPE was stronger than 15-HEPE, targeting 24 genes, mainly at the earliest stages of embryo development (at the blastula and swimming blastula stages). These findings highlight the differences between HEPEs and PUAs and also have important ecological implications because many diatom species do not produce PUAs, but rather these other chemicals are derived from the oxidation of fatty acids.

Maternal Exposure to Cadmium and Manganese Impairs Reproduction and Progeny Fitness in the Sea Urchin Paracentrotus lividus

Metal contamination represents one of the major sources of pollution in marine environments. In this study we investigated the short-term effects of ecologically relevant cadmium and manganese concentrations (10^-6 and 3.6 x 10^-5 M, respectively) on females of the sea urchin Paracentrotus lividus and their progeny, reared in the absence or presence of the metal. Cadmium is a well-known heavy metal, whereas manganese represents a potential emerging contaminant, resulting from an increased production of manganese-containing compounds. The effects of these agents were examined on both P. lividus adults and their offspring following reproductive state, morphology of embryos, nitric oxide (NO) production and differential gene expression. Here, we demonstrated that both metals differentially impaired the fertilization processes of the treated female sea urchins, causing modifications in the reproductive state and also affecting NO production in the ovaries. A detailed analysis of the progeny showed a high percentage of abnormal embryos, associated to an increase in the endogenous NO levels and variations in the transcriptional expression of several genes involved in stress response, skeletogenesis, detoxification, multi drug efflux processes and NO production. Moreover, we found significant differences in the progeny from females exposed to metals and reared in metal-containing sea water compared to embryos reared in non-contaminated sea water. Overall, these results greatly expanded previous studies on the toxic effects of metals on P. lividus and provided new insights into the molecular events induced in the progeny of sea urchins exposed to metals.

Characterization and Endocytic Internalization of Epith-2 Cell Surface Glycoprotein during the Epithelial-to-Mesenchymal Transition in Sea Urchin Embryos

The epithelial cells of the sea urchin Hemicentrotus pulcherrimus embryo express an Epith-2, uncharacterized glycoprotein, on the lateral surface. Here, we describe internalization of Epith-2 during mesenchyme formation through the epithelial-to-mesenchymal transition (EMT). Epith-2 was first expressed on the entire egg surface soon after fertilization and on the blastomeres until the 4-cell stage, but was localized to the lateral surface of epithelial cells at and after the 16-cell stage throughout the later developmental period. However, primary mesenchyme cells (PMC) and secondary mesenchyme cells (SMC) that ingress by EMT lost Epith-2 from their cell surface by endocytosis during dissociation from the epithelium, which was associated with the appearance of cytoplasmic Epith-2 dots. The cytoplasmic Epith-2 retained a similar relative molecular mass to that of the cell surface immediately after ingression through the early period of the spreading to single cells. Then, Epith-2 was completely lost from the cytoplasm. Tyrosine residues of Epith-2 were phosphorylated. The endocytic retraction of Epith-2 was inhibited by herbimycin A (HA), a protein tyrosine kinase (PTK) inhibitor, and suramin, a growth factor receptor (GFR) inhibitor, suggesting the involvement of the GFR/PTK (GP) signaling pathway. These two GP inhibitors also inhibited PMC and SMC spreading to individual cells after ingression, but the dissociation of PMC and SMC from the epithelium was not inhibited. In suramin-treated embryos, dissociated mesenchyme cells migrated partially by retaining their epithelial morphology. In HA-treated embryos, no mesenchyme cells migrated. Thus, the EMT occurs in relation to internalization of Epith-2 from presumptive PMC and SMC.

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.

High ordered biomineralization induced by carbon nanoparticles in the sea urchin Paracentrotus lividus

A surprising and unexpected biomineralization process was observed during toxicological assessment of carbon nanoparticles on Paracentrotus lividus (sea urchin) pluteus larvae. The larvae activate a process of defense against external material, by incorporating the nanoparticles into microstructures of aragonite similarly to pearl oysters. Aiming at a better understanding of this phenomenon, the larvae were exposed to increasing concentrations of carbon nanoparticles and the biomineralization products were analyzed by electron microscopy, x-ray diffraction and Raman spectroscopy. In order to evaluate the possible influence of Sp-CyP-1 expression on this biomineralization process by larvae, analyses of gene expression (Sp-CyP-1) and calcein labeling were performed. Overall, we report experimental evidence about the capability of carbon nanoparticles to induce an increment of Sp-CyP-1 expression with the consequent activation of a biomineralization process leading to the production of a new pearl-like biomaterial never previously observed in sea urchins.

Defensome against toxic diatom aldehydes in the sea urchin Paracentrotus lividus

Many diatom species produce polyunsaturated aldehydes, such as decadienal, which compromise embryonic and larval development in benthic organisms. Here newly fertilized Paracentrotus lividus sea urchins were exposed to low concentration of decadienal and the expression levels of sixteen genes, implicated in a broad range of functional responses, were followed by Real Time qPCR in order to identify potential decadienal targets. We show that at low decadienal concentrations the sea urchin Paracentrotus lividus places in motion different classes of genes to defend itself against this toxic aldehyde, activating hsp60 and two proteases, hat and BP10, at the blastula stage and hsp56 and several other genes (14-3-3ε, p38 MAPK, MTase, and GS) at the prism stage. At this latter stage all genes involved in skeletogenesis (Nec, uni, SM50 and SM30) were also down-expressed, following developmental abnormalities that mainly affected skeleton morphogenesis. Moreover, sea urchin embryos treated with increasing concentrations of decadienal revealed a dose-dependent response of activated target genes. Finally, we suggest that this orchestrated defense system against decadienal represents part of the chemical defensome of P. lividus affording protection from environmental toxicants.

Stress response gene activation protects sea urchin embryos exposed to X-rays

We used Paracentrotus lividus sea urchin embryos, a well-established model in developmental biology and ecotoxicology, for investigation on stress/anti-apoptotic protein expression elicited in response to harmful ionizing radiation, such as X-rays. We evaluated the acute effects of a high-dose exposure (5 Gy) on P. lividus analyzing by Western blotting the accumulation levels of HSP60, HSP70, BAG3 and a putative p63 at 24 and 48 h after irradiation. We found an increase in the HSP70, BAG3, and p63 protein levels only 48 h after irradiation, whereas no HSP60 increase was detected either at 24 or 48 h. Levels of the mRNA coding for HSP70 and p63 were also investigated by relative RT-PCR and were found to increase 24 h after irradiation, returning to their initial levels at 48 h. Results demonstrate the presence of an adaptive regulatory mechanism operating at the transcriptional level at 24 h, followed by a translational activation at 48 h post-irradiation. In conclusion, our findings confirm the sea urchin embryo as a sensible bioindicator of cell damage and we propose this model for studies on the protective pathways activated in response to X-rays. The novel result of the involvement of BAG3 and p63 in the response to X-rays, never tested so far in any other embryonic system, opens the way for their use as biomarkers of X-ray hazards.

Embryonic development and skeletogenic gene expression affected by X-rays in the Mediterranean sea urchin Paracentrotus lividus

International concern over environmental nuclear contamination of salt water fisheries and coastal resources has attracted the interests of ecologists, marine biologists and stakeholders. There are not many studies on the effects of X-rays, a component of radionuclides emissions, on embryonic development and gene expression. The sea urchin embryo is emerging as a useful model system for environmental and eco-toxicological studies. Here, we describe how X-rays affect development and gene expression in embryos of the Mediterranean sea urchin Paracentrotus lividus. Cleavage embryos were exposed to doses from 0.1 to 5 Gy, using an Ag source of X radiation. We found a dose-dependent increase in developmental delays and severe morphological defects in embryos microscopically inspected at two endpoints, 24 and 48 h after irradiation. By analogy with classical toxicity tests parameters we defined the No Observed Effect Dose at 0.1 Gy, the Lowest Observed Effect Dose at 0.5 Gy and ED50 at 1.0 Gy. Major perturbations concerned primitive intestine and skeleton differentiation and development: X-rays exposed embryos had both no gut and arms or poorly and abnormally developed ones. We found a dose-dependent reduction in the mRNA levels of two skeleton-specific genes, Pl-SM30 (spicule matrix 30) and Pl-msp130 (matrix spicule protein 130), as measured by semi-quantitative RT-PCR and whole mount in situ hybridization, respectively. These findings indicate the sea urchin embryo as a sensible bioindicator of X-radiation and propose its use as an alternative model, emphasizing the need for further investigation aimed to protect ecosystem health.

Pl-nectin, a discoidin family member, is a ligand for betaC integrins in the sea urchin embryo

Pl-nectin is a component of the extracellular matrix that surrounds embryos of the sea urchin Paracentrotus lividus. Pl-nectin mediates adhesion of dissociated embryonic cells to substrates and interfering with ectodermic cells contacting Pl-nectin results in defects in skeleton growth and morphogenesis. Recently, we reported that Pl-nectin is a new member of the discoidin family, in agreement with the notion that many discoidin-containing proteins are involved in cell adhesion processes as integrin ligands. To better understand the molecular basis for the interaction of Pl-nectin with ectoderm, we investigated the hypothesis that Pl-nectin is an integrin ligand in sea urchin embryos. We show that in P. lividus embryos, betaC-containing integrins localize to the apical surface of ectodermic cells, which are in contact with Pl-nectin. Immunoprecipitation experiments indicate that the two proteins are part of a complex in vivo and affinity chromatography indicates that betaC-containing integrin receptors bind purified Pl-nectin. These data support a model in which ectodermic integrins binding to Pl-nectin mediate cellular adhesion to the hyaline layer. Regulated adhesion of cells to the hyaline layer is a critical component of several morphogenetic processes and the identification of the receptors and ligands involved provides new opportunities to investigate the underlying molecular mechanisms of ECM adhesion and morphogenesis.

Cloning, sequencing of bone morphogenetic protein from sea urchin, Hemicentrotus pulcherrimus

A cDNA coding for bone morphogenetic protein (BMP) homolog of the sea urchin, Hemicentrotus pulcherrimus, was isolated from mid-gastrula using reverse transcription-polymerase chain reaction (RT-PCR) technique. The 2314 nucleotide sequence contains a 1383 open reading frame corresponding to a translation product of 461 amino acids. Comparison of the nucleotide and deduced amino acid sequence with BMP isolated from Strongylocentrotus purpuratus (SpBMP5-7; accession No. Z48313) shows a high degree of conservation. HpBMP seems to belong to the 60A subgroup as a result. A mRNA coding H. pulcherrimus BMP (HpBMP) was not detected in the unfertilized egg, but it was detected from blastula to prism stages.

Gene expression patterns in a novel animal appendage: the sea urchin pluteus arm

The larval arms of echinoid plutei are used for locomotion and feeding. They are composed of internal calcite skeletal rods covered by an ectoderm layer bearing a ciliary band. Skeletogenesis includes an autonomous molecular differentiation program in primary mesenchyme cells (PMCs), initiated when PMCs leave the vegetal plate for the blastocoel, and a patterning of the differentiated skeletal units that requires molecular cues from the overlaying ectoderm. The arms represent a larval feature that arose in the echinoid lineage during the Paleozoic and offers a subject for the study of gene co-option in the evolution of novel larval features. We isolated new molecular markers in two closely related but differently developing species, Heliocidaris tuberculata and Heliocidaris erythrogramma. We report the expression of a larval arm-associated ectoderm gene tetraspanin, as well as two new PMC markers, advillin and carbonic anhydrase. Tetraspanin localizes to the animal half of blastula stage H. tuberculata and then undergoes a restriction into the putative oral ectoderm and future location of the postoral arms, where it continues to be expressed at the leading edge of both the postoral and anterolateral arms. In H. erythrogramma, its expression initiates in the animal half of blastulae and expands over the entire ectoderm from gastrulation onward. Advillin and carbonic anhydrase are upregulated in the PMCs postgastrulation and localized to the leading edge of the growing larval arms of H. tuberculata but do not exhibit coordinated expression in H. erythrogramma larvae. The tight spatiotemporal regulation of these genes in H. tuberculata along with other ontogenetic and phylogenetic evidence suggest that pluteus arms are novel larval organs, distinguishable from the processes of skeletogenesis per se. The dissociation of expression control in H. erythrogramma suggest that coordinate gene expression in H. tuberculata evolved as part of the evolution of pluteus arms, and is not required for larval or adult development.

RTK and TGF-beta signaling pathways genes in the sea urchin genome

The Receptor Tyrosine kinase (RTK) and TGF-beta signaling pathways play essential roles during development in many organisms and regulate a plethora of cellular responses. From the genome sequence of Strongylocentrotus purpuratus, we have made an inventory of the genes encoding receptor tyrosine kinases and their ligands, and of the genes encoding cytokines of the TGF-beta superfamily and their downstream components. The sea urchin genome contains at least 20 genes coding for canonical receptor tyrosine kinases. Seventeen of the nineteen vertebrate RTK families are represented in the sea urchin. Fourteen of these RTK among which ALK, CCK4/PTK7, DDR, EGFR, EPH, LMR, MET/RON, MUSK, RET, ROR, ROS, RYK, TIE and TRK are present as single copy genes while pairs of related genes are present for VEGFR, FGFR and INSR. Similarly, nearly all the subfamilies of TGF-beta ligands identified in vertebrates are present in the sea urchin genome including the BMP, ADMP, GDF, Activin, Myostatin, Nodal and Lefty, as well as the TGF-beta sensu stricto that had not been characterized in invertebrates so far. Expression analysis indicates that the early expression of nodal, BMP2/4 and lefty is restricted to the oral ectoderm reflecting their role in providing positional information along the oral-aboral axis of the embryo. The coincidence between the emergence of TGF-beta-related factors such as Nodal and Lefty and the emergence of the deuterostome lineage strongly suggests that the ancestral function of Nodal could have been related to the secondary opening of the mouth which characterizes this clade, a hypothesis supported by functional data in the extant species. The sea urchin genome contains 6 genes encoding TGF-beta receptors and 4 genes encoding prototypical Smad proteins. Furthermore, most of the transcriptional activators and repressors shown to interact with Smads in vertebrates have orthologues in echinoderms. Finally, the sea urchin genome contains an almost complete repertoire of genes encoding extracellular modulators of BMP signaling including Chordin, Noggin, Sclerotin, SFRP, Gremlin, DAN and Twisted gastrulation. Taken together, these findings indicate that the sea urchin complement of genes of the RTK and TGF-beta signaling pathways is qualitatively very similar to the repertoire present in vertebrates, and that these genes are part of the common genetool kit for intercellular signaling of deuterostomes.

Sea urchin metalloproteases: a genomic survey of the BMP-1/tolloid-like, MMP and ADAM families

Analysis of the Strongylocentrotus purpuratus genome has revealed approximately 240 metalloprotease genes, and they represent all 23 families expressed in vertebrates. EST/cDNA sequencing and microarray analysis show that nearly 70% are represented in embryo RNA. Among them are many metalloproteases with demonstrated developmental roles in other systems-BMP-1/TLD (tolloid) (astacins), MMPs (matrix metalloproteases) and the ADAMs (disintegrin/metalloproteases). The developmental functions of these kinds of metalloproteases include modifying the extracellular matrix, regulating signaling pathways or modulating cellular adhesive properties. The unexpectedly large number of BMP-1/TLD-like protease genes (23) results primarily from expansion of a set encoding an unusual domain conserved in structure and primary sequence only in nematode astacins. Such proteases may have interesting developmental functions because the expression patterns of several are highly regulated along the primary axis at times when cell differentiation and morphogenesis begin. The size of the sea urchin MMP family and the clustered arrangement of many of its members are similar to vertebrates, but phylogenetic analyses suggest that different ancestral genes were independently amplified in sea urchins and vertebrates. One expansion appears to be genes encoding MMPs that have putative transmembrane domains and may be membrane-tethered (MT). Interestingly, the genes encoding TIMPs, inhibitors of MMPs, have also been amplified and the 10 genes are tandemly arranged in a single cluster. In contrast, there are fewer ADAM and ADAMTS genes in sea urchins, but they represent all but one of the chordate-specific groups. The genome sequence now opens the door to experimental manipulations designed to understand how modulation of the extracellular environment affects development.

Afuni, a novel transforming growth factor-β gene is involved in arm regeneration by the brittle star Amphiura filiformis

The bone morphogenetic proteins (BMPs) are a family of the transforming growth factor-beta (TGF-beta) superfamily that perform multiple roles during vertebrate and invertebrate development. Here, we report the molecular cloning of a novel BMP from regenerating arms of the ophiuroid Amphiura filiformis. The theoretically translated amino acid sequence of this novel BMP has high similarity to that of the sea urchin BMP univin. This novel BMP has been named afuni. Whole-mount in situ hybridisation implicates afuni in arm regeneration. Expression occurs in distinct proximal and distal regions of late regenerates (3- and 5-week postablation). These sites are at different stages of regeneration, suggesting multiple roles for this gene in adult arm development. Cellular expression of this gene occurs in migratory cells within the radial water canal (RWC) of regenerating and nonregenerating arms. These migrating coelomocytes suggest a key role for the coelomic RWC as a source of the cellular material for use in arm regeneration by A. filiformis.

UVB radiation prevents skeleton growth and stimulates the expression of stress markers in sea urchin embryos

Ozone depletion results in an increased flux of biologically damaging radiations reaching the earth. Although ultraviolet (UV) penetration is attenuated by the seawater, harmful effects can be still observed at low depths where sea urchin embryos are living. We have used Paracentrotus lividus embryos to study the impacts of UV radiation on their development. Blastula cultures were exposed to different doses of UVB (312 nm) radiations and the resulting endpoint effects were evaluated in terms of embryonic morphological abnormalities, variations in specific gene expression, and changes in the levels of stress proteins. We found that embryos were moderately sensitive to 50 J/m2 UVB radiation; an increase in the number of developmentally delayed and malformed embryos was detected when increasing doses, up to 1000 J/m2, were used. Major developmental defects, observed 24 and 48 h after exposure, consisted in the failure of skeleton elongation and patterning. Accordingly, we found a reduction in the number of primary mesenchyme cells that expressed Pl-SM30, a gene coding for one of the specific matrix proteins of the skeleton. The morphological effects observed 1, 24, and 48 h after exposure were correlated with a dose-dependent increase in the level and in the activation of two recognized stress markers, namely hsp70 and p38 MAPk, respectively, consistent with their role in mediating cellular response to stress and suggesting a function in embryo survival.

Cell adhesion and communication: a lesson from echinoderm embryos for the exploitation of new therapeutic tools

In this chapter, we summarise fundamental findings concerning echinoderms as well as research interests on this phylum for biomedical and evolutionary studies. We discuss how current knowledge of echinoderm biology, in particular of the sea urchin system, can shed light on the understanding of important biological phenomena and in dissecting them at the molecular level. The general principles of sea urchin embryo development are summarised, mainly focusing on cell communication and interactions, with particular attention to the cell-extracellular matrix and cell-cell adhesion molecules and related proteins. Our purpose is not to review all the work done over the years in the field of cellular interaction in echinoderms. On the contrary, we will rather focus on a few arguments in an effort to re-examine some ideas and concepts, with the aim of promoting discussion in this rapidly growing field and opening new routes for research on innovative therapeutic tools.

Nodal/activin signaling establishes oral-aboral polarity in the early sea urchin embryo

Components of the Wnt signaling pathway are involved in patterning the sea urchin primary or animal-vegetal (AV) axis, but the molecular cues that pattern the secondary embryonic axis, the aboral/oral (AO) axis, are not known. In an analysis of signaling molecules that influence patterning along the sea urchin embryonic axes, we found that members of the activin subfamily of transforming growth factor-beta (TGF-beta) signaling molecules influence the establishment of AO polarities in the early embryo. Injection of activin mRNAs into fertilized eggs or treatment with exogenously applied recombinant activin altered the allocation of ectodermal fates and ventralized the embryo. The phenotypes observed resemble the ventralized phenotype previously reported for NiCl2, a known disrupter of AO patterning. Sensitivity to exogenous activin occurs between fertilization and the late blastula stage, which is also the time of highest NiCl2 sensitivity. These results argue that specification of fates along the embryonic AO axis involves TGF-beta signaling. To further examine TGF-beta signaling in these embryos, we cloned an endogenous TGF-beta from sea urchin embryos that is a member of the activin subfamily, SpNodal, and show through gain of function analysis that it recapitulates results obtained with exogenous activins and NiCl2. The expression pattern of SpNodal is consistent with a role for nodal signaling in the establishment of fates along the AO axis. Loss of function experiments using SpNodal antisense morpholinos also support a role for SpNodal in the establishment of the AO axis.

Commitment and response to inductive signals of primary mesenchyme cells of the sea urchin embryo

In the sea urchin embryo, primary mesenchyme cells (PMC) are committed to produce the larval skeleton, although their behavior and skeleton production are influenced by signals from the embryonic environment. Results from our recent studies showed that perturbation of skeleton development, by interfering with ectoderm-extracellular matrix (ECM) interactions, is linked to a reduction in the gene expression of a transforming growth factor (TGF)-beta growth factor, Pl-univin, suggesting a reduction in the blastocoelic amounts of the protein and its putative involvement in signaling events. In the present study, we examined PMC competence to respond to environmental signals in a validated skeleton perturbation model in Paracentrotus lividus. We found that injection of blastocoelic fluid (BcF), obtained from normal embryos, into the blastocoelic cavity of skeleton-defective embryos rescues skeleton development. In addition, PMC from skeleton-defective embryos transplanted into normal or PMC-less blastula embryos are able to position in correct regions of the blastocoel and to engage spicule elongation and patterning. Taken together, these results demonstrate that PMC commitment to direct skeletogenesis is maintained in skeleton perturbed embryos and confirm the role played by inductive signals in regulating skeleton growth and shape.