ATP-binding cassette (ABC) transporter expression and localization in sea urchin development

MAPK signaling pathway enhances tolerance of Mytilus galloprovincialis to co-exposure of sulfamethoxazole and polyethylene microplastics

Microplastics (MPs) and antibiotics often coexist in complex marine environments, yet their combined detrimental effects on marine organisms remain underexplored. This study evaluated the effects of polyethylene microplastics (PE, 200 μg/L) and sulfamethoxazole (SMX, 50 μg/L), both individually and in combination, on Mytilus galloprovincialis. The exposure lasted 6 days, followed by a 6-day recovery period. Bioaccumulation, DNA damage, pollutants transport/metabolism related responses and responding alterations of mitogen-activated protein kinase (MAPK) signaling pathway were detected in gills and digestive glands. Bioaccumulation of SMX/PE in mussels occurred in a tissue-specific manner, co-exposure altered SMX contents in investigated tissues. Co-exposure did not induce extra DNA damage, elevated DNA damage was alleviated during the recovery period in all treated groups. The exposure of SMX/PE exerted different alterations in pollutants transport/metabolism related responses, characterized by multixenobiotic resistance and relative expression of key genes (cytochrome P450 monooxygenase, glutathione S-transferase, ATP-binding cassette transporters). Key molecules (p38 MAPK, c-jun N-terminal kinase, extracellular regulated protein kinase, nuclear factor-κB and tumor protein p53) in MAPK signaling pathway were activated at transcriptional and translational levels after SMX/PE and co-exposure. Co-regulation between MAPK members and pollutants transport/metabolism related factors was revealed, suggesting MAPK signaling pathway served as a regulating hub in exposed mussels to conquer SMX/PE stress. Overall, this study provides new insights on SMX/PE induced health risks in marine mussels and potential mechanism through MAPK cascades regulation.

Transcriptomic and metabolomic analyses reveal sex-related differences in the gonads of Pinctada fucata martensii

Pinctada fucata martensii is an economically important bivalve mollusk, as this species makes a major contribution to seawater pearl production. Pearl production efficiency varies between the sexes of P. f. martensii, but many aspects of the molecular mechanisms underlying sex determination and sex differentiation in P. f. martensii remain unclear. Here, transcriptomic and metabonomic analyses were conducted to identify the major genes and metabolic changes associated with sex determination and gametogenesis. We identified a total of 3426 differentially expressed genes (DEGs) between females and males. These included Fem-1c and Foxl2, which are involved in sex determination and sex differentiation, and SOHLH2, Nanos1 and TSSK4, which are involved in gametogenesis. We also identified a total of 5231 significant differential metabolites (SDMs) between females and males. These DEGs were enriched in 47 metabolic pathways, including "ABC transporters," "purine metabolism," and "glycerophospholipid metabolism." Our findings provide new insights into the molecular mechanisms underlying sex determination, sex differentiation, and gametogenesis and will aid future studies of P. f. martensii.

Echinobase: a resource to support the echinoderm research community

Echinobase (www.echinobase.org) is a model organism knowledgebase serving as a resource for the community that studies echinoderms, a phylum of marine invertebrates that includes sea urchins and sea stars. Echinoderms have been important experimental models for over 100 years and continue to make important contributions to environmental, evolutionary, and developmental studies, including research on developmental gene regulatory networks. As a centralized resource, Echinobase hosts genomes and collects functional genomic data, reagents, literature, and other information for the community. This third-generation site is based on the Xenbase knowledgebase design and utilizes gene-centric pages to minimize the time and effort required to access genomic information. Summary gene pages display gene symbols and names, functional data, links to the JBrowse genome browser, and orthology to other organisms and reagents, and tabs from the Summary gene page contain more detailed information concerning mRNAs, proteins, diseases, and protein-protein interactions. The gene pages also display 1:1 orthologs between the fully supported species Strongylocentrotus purpuratus (purple sea urchin), Lytechinus variegatus (green sea urchin), Patiria miniata (bat star), and Acanthaster planci (crown-of-thorns sea star). JBrowse tracks are available for visualization of functional genomic data from both fully supported species and the partially supported species Anneissia japonica (feather star), Asterias rubens (sugar star), and L. pictus (painted sea urchin). Echinobase serves a vital role by providing researchers with annotated genomes including orthology, functional genomic data aligned to the genomes, and curated reagents and data. The Echinoderm Anatomical Ontology provides a framework for standardizing developmental data across the phylum, and knowledgebase content is formatted to be findable, accessible, interoperable, and reusable by the research community.

The roles of ABCB1/P-glycoprotein drug transporters in regulating gut microbes and inflammation: insights from animal models, old and new

Commensal enteric bacteria have evolved systems that enable growth in the ecologic niche of the host gastrointestinal tract. Animals evolved parallel mechanisms to survive the constant exposure to bacteria and their metabolic by-products. We propose that drug transporters encompass a crucial system to managing the gut microbiome. Drug transporters are present in the apical surface of gut epithelia. They detoxify cells from small molecules and toxins (xenobiotics) in the lumen. Here, we review what is known about commensal structure in the absence of the transporter ABCB1/P-glycoprotein in mammalian models. Knockout or low-activity alleles of ABCB1 lead to dysbiosis, Crohn's disease and ulcerative colitis in mammals. However, the exact function of ABCB1 in these contexts remain unclear. We highlight emerging models-the zebrafish Danio rerio and sea urchin Lytechinus pictus-that are poised to help dissect the fundamental mechanisms of ATP-binding cassette (ABC) transporters in the tolerance of commensal and pathogenic communities in the gut. We and others hypothesize that ABCB1 plays a direct role in exporting inflammatory bacterial products from host epithelia. Interdisciplinary work in this research area will lend novel insight to the transporter-mediated pathways that impact microbiome community structure and accelerate the pathogenesis of inflammatory bowel disease when perturbed. This article is part of the theme issue 'Sculpting the microbiome: how host factors determine and respond to microbial colonization'.

Solute carrier (SLC) expression reveals skeletogenic cell diversity

Within the developing embryo is a microcosm of cell type diversity. Single cell RNA-sequencing (scRNA-seq) is used to reveal cell types, typically by grouping cells according to their gene regulatory states. However, both across and within these regulatory states are additional layers of cellular diversity represented by the differential expression of genes that govern cell function. Here, we analyzed scRNA-seq data representing the late gastrula stage of Strongylocentrotus purpuratus (purple sea urchin) to understand the patterning of transporters belonging to the ABC and SLC families. These transporters handle diverse substrates from amino acids to signaling molecules, nutrients and xenobiotics. Using transporter-based clustering, we identified unique transporter patterns that are both shared across cell lineages, as well as those that were unique to known cell types. We further explored three patterns of transporter expression in mesodermal cells including secondary mesenchyme cells (pigment cells and blastocoelar cells) and skeletogenic cells (primary mesenchyme cells). The results revealed the enrichment of SMTs potentially involved in nutrient absorption (SLC5A9, SLC7A11, SLC35F3, and SLC52A3) and skeletogenesis (SLC9A3, SLC13A2/3/5, and SLC39A13) in pigment cells and blastocoelar cells respectively. The results indicated that the strategy of clustering by cellular activity can be useful for discovering cellular populations that would otherwise remain obscured.

An ATP-binding cassette transporter G2 (CgABCG2) regulates the haemocyte proliferation by modulating the G1/S phase transition of cell cycle in oyster Crassostrea gigas

ATP-binding cassette transporter G2 (ABCG2) is a half-transporter of the G subfamily in ATP-binding cassette transporters (ABC transporter), which is involved in the regulation of multidrug-resistant, cell cycle, and cell proliferation. In the present study, a homologue of ABCG2 (named as CgABCG2) with the conserved AAA domain and ABC2 membrane domain was identified from the Pacific oyster Crassostrea gigas. The open reading frame (ORF) of CgABCG2 was of 1956 bp encoding a predicted polypeptide of 652 amino acids, which shared 56.7%-65.7% sequence similarities with previously identified ABCG2s from other animals. The mRNA transcripts of CgABCG2 were detected in all the tested tissues with higher expression levels in gonad and haemocytes (19.31-fold and 11.23-fold of that in adductor muscle respectively, p < 0.05). CgABCG2 was mainly distributed on the cell membrane of the haemocytes with a partial distribution in the cytoplasm and nucleus. After Vibrio splendidus stimulation, the mRNA expression level of CgABCG2 in haemocytes was significantly up-regulated at 3 h and 6 h, which was 5.22-fold and 8.60-fold (p < 0.05) of that in control, respectively. After the expression of CgABCG2 was interfered by RNAi, the number of cells with EdU positive signals was reduced in both haemocytes and the potential hematopoietic sites. And the mRNA expression level of CgPCNA, CgGATA3, CgRunx, CgSCL and CgC-kit decreased significantly (p < 0.05), which were about 0.66-, 0.37-, 0.32-, 0.50-, and 0.50-fold of that in the negative control group, respectively. While the mRNA expression level of CgCDK2 increased significantly (1.84-fold to that in control, p < 0.05) and that of stem cell-related factor CgSOX2 did not change significantly in the si-CgABCG2 oysters. Moreover, the cell cycle of haemocytes was detected by flow cytometry, which was arrested at G0/G1 phase in the si-CgABCG2 oysters. All the results collectively suggested that CgABCG2 might involve the proliferation of haemocytes by regulating the expression of haematopoiesis related transcription factors and the G1/S phase transition of the cell cycle in oyster C. gigas.

Early expression onset of tissue-specific effector genes during the specification process in sea urchin embryos

BACKGROUND

In the course of animal developmental processes, various tissues are differentiated through complex interactions within the gene regulatory network. As a general concept, differentiation has been considered to be the endpoint of specification processes. Previous works followed this view and provided a genetic control scheme of differentiation in sea urchin embryos: early specification genes generate distinct regulatory territories in an embryo to express a small set of differentiation driver genes; these genes eventually stimulate the expression of tissue-specific effector genes, which provide biological identity to differentiated cells, in each region. However, some tissue-specific effector genes begin to be expressed in parallel with the expression onset of early specification genes, raising questions about the simplistic regulatory scheme of tissue-specific effector gene expression and the current concept of differentiation itself.

RESULTS

Here, we examined the dynamics of effector gene expression patterns during sea urchin embryogenesis. Our transcriptome-based analysis indicated that many tissue-specific effector genes begin to be expressed and accumulated along with the advancing specification GRN in the distinct cell lineages of embryos. Moreover, we found that the expression of some of the tissue-specific effector genes commences before cell lineage segregation occurs.

CONCLUSIONS

Based on this finding, we propose that the expression onset of tissue-specific effector genes is controlled more dynamically than suggested in the previously proposed simplistic regulation scheme. Thus, we suggest that differentiation should be conceptualized as a seamless process of accumulation of effector expression along with the advancing specification GRN. This pattern of effector gene expression may have interesting implications for the evolution of novel cell types.

Generation of a homozygous mutant drug transporter (ABCB1) knockout line in the sea urchin Lytechinus pictus

Sea urchins are premier model organisms for the study of early development. However, the lengthy generation times of commonly used species have precluded application of stable genetic approaches. Here, we use the painted sea urchin Lytechinus pictus to address this limitation and to generate a homozygous mutant sea urchin line. L. pictus has one of the shortest generation times of any currently used sea urchin. We leveraged this advantage to generate a knockout mutant of the sea urchin homolog of the drug transporter ABCB1, a major player in xenobiotic disposition for all animals. Using CRISPR/Cas9, we generated large fragment deletions of ABCB1 and used these readily detected deletions to rapidly genotype and breed mutant animals to homozygosity in the F2 generation. The knockout larvae are produced according to expected Mendelian distribution, exhibit reduced xenobiotic efflux activity and can be grown to maturity. This study represents a major step towards more sophisticated genetic manipulation of the sea urchin and the establishment of reproducible sea urchin animal resources.

Combined exposure to microplastics and zinc produces sex-specific responses in the water flea Daphnia magna

Microplastics are ubiquitous environmental pollutants and a great threat to the aquatic environment. Due to their small size (ranging from 1 µm to 5 mm), microplastics be easily ingested by a wide range of organisms and can serve as a vector for various contaminants. In this study, additive or possible synergistic effects of microplastics and zinc were demonstrated through sex-specific alterations in behavior, redox status, and modulation of detoxification-related genes in Daphnia magna, with males being more sensitive than females with stronger modulations of antioxidant responses, particularly on glutathione S-transferases expressions. Furthermore, we demonstrated microplastics may act as vectors for metals (Zn²⁺) in the aquatic environment in D. magna, with reduced bio-concentration of the total Zn concentration, inducing greater toxicity. Our findings demonstrated synergistic toxicity of the heavy metal Zn and microplastics and could contribute to greater understanding of sex-specific effects of microplastics in aquatic organisms.

Chromosomal-Level Genome Assembly of the Painted Sea Urchin Lytechinus pictus: A Genetically Enabled Model System for Cell Biology and Embryonic Development

The painted urchin Lytechinus pictus is a sea urchin in the family Toxopneustidae and one of several sea urchin species that are routinely used as an experimental research organism. Recently, L. pictus has emerged as a tractable model system for establishing transgenic sea urchin lines due to its amenability to long term laboratory culture. We present the first published genome of L. pictus. This chromosomal-level assembly was generated using Illumina sequencing in conjunction with Oxford Nanopore Technologies long read sequencing and HiC chromatin conformation capture sequencing. The 998.9-Mb assembly exhibits high contiguity and has a scaffold length N50 of 46.0 Mb with 97% of the sequence assembled into 19 chromosomal-length scaffolds. These 19 scaffolds exhibit a high degree of synteny compared with the 19 chromosomes of a related species Lytechinus variegatus. Ab initio and transcript evidence gene modeling, combined with sequence homology, identified 28,631 gene models that capture 92% of BUSCO orthologs. This annotation strategy was validated by manual curation of gene models for the ABC transporter superfamily, which confirmed the completeness and accuracy of the annotations. Thus, this genome assembly, in conjunction with recent high contiguity assemblies of related species, positions L. pictus as an exceptional model system for comparative functional genomics and it will be a key resource for the developmental, toxicological, and ecological biology scientific communities.

CRISPR/Cas9 mutagenesis reveals a role for ABCB1 in gut immune responses to Vibrio diazotrophicus in sea urchin larvae

The ABC transporter ABCB1 plays an important role in the disposition of xenobiotics. Embryos of most species express high levels of this transporter in early development as a protective mechanism, but its native substrates are not known. Here, we used larvae of the sea urchin Strongylocentrotus purpuratus to characterize the early life expression and role of Sp-ABCB1a, a homolog of ABCB1. The results indicate that while Sp-ABCB1a is initially expressed ubiquitously, it becomes enriched in the developing gut. Using optimized CRISPR/Cas9 gene editing methods to achieve high editing efficiency in the F0 generation, we generated ABCB1a crispant embryos with significantly reduced transporter efflux activity. When infected with the opportunistic pathogen Vibrio diazotrophicus, Sp-ABCB1a crispant larvae demonstrated significantly stronger gut inflammation, immunocyte migration and cytokine Sp-IL-17 induction, as compared with infected control larvae. The results suggest an ancestral function of ABCB1 in host-microbial interactions, with implications for the survival of invertebrate larvae in the marine microbial environment.

Early patterning of ABCB, ABCC, and ABCG transporters establishes unique territories of small molecule transport in embryonic mesoderm and endoderm

Directed intercellular movement of diverse small molecules, including metabolites, signal molecules and xenobiotics, is a key feature of multicellularity. Networks of small molecule transporters (SMTs), including several ATP Binding Cassette (ABC) transporters, are central to this process. While small molecule transporters are well described in differentiated organs, little is known about their patterns of expression in early embryogenesis. Here we report the pattern of ABC-type SMT expression and activity during the early development of sea urchins. Of the six major ABCs in this embryo (ABCB1, -B4, -C1, -C4, -C5 and -G2), three expression patterns were observed: 1) ABCB1 and ABCC1 are first expressed ubiquitously, and then become enriched in endoderm and ectoderm-derived structures. 2) ABCC4 and ABCC5 are restricted to a ring of mesoderm in the blastula and ABCC4 is later expressed in the coelomic pouches, the embryonic niche of the primordial germ cells. 3) ABCB4 and ABCG2 are expressed exclusively in endoderm-fated cells. Assays with fluorescent substrates and inhibitors of transporters revealed a ring of ABCC4 efflux activity emanating from ABCC4⁺ mesodermal cells. Similarly, ABCB1 and ABCB4 efflux activity was observed in the developing gut, prior to the onset of feeding. This study reveals the early establishment of unique territories of small molecule transport during embryogenesis. A pattern of ABCC4/C5 expression is consistent with signaling functions during gut invagination and germ line development, while a later pattern of ABCB1/B4 and ABCG2 is consistent with roles in the embryonic gut. This work provides a conceptual framework with which to examine the function and evolution of SMT networks and to define the specific developmental pathways that drive the expression of these genes.

Disruption of small molecule transporter systems by Transporter-Interfering Chemicals (TICs)

Small molecule transporters (SMTs) in the ABC and SLC families are important players in disposition of diverse endo- and xenobiotics. Interactions of environmental chemicals with these transporters were first postulated in the 1990s, and since validated in numerous in vitro and in vivo scenarios. Recent results on the co-crystal structure of ABCB1 with the flame-retardant BDE-100 demonstrate that a diverse range of man-made and natural toxic molecules, hereafter termed transporter-interfering chemicals (TICs), can directly bind to SMTs and interfere with their function. TIC-binding modes mimic those of substrates, inhibitors, modulators, inducers, and possibly stimulants through direct and allosteric mechanisms. Similarly, the effects could directly or indirectly agonize, antagonize or perhaps even prime the SMT system to alter transport function. Importantly, TICs are distinguished from drugs and pharmaceuticals that interact with transporters in that exposure is unintended and inherently variant. Here, we review the molecular mechanisms of environmental chemical interaction with SMTs, the methodological considerations for their evaluation, and the future directions for TIC discovery.

Evolutionary history of ATP-binding cassette proteins

ATP-binding cassette (ABC) proteins are found in every sequenced genome and evolved deep in the phylogenetic tree of life. ABC proteins form one of the largest homologous protein families, with most being involved in substrate transport across biological membranes, and a few cytoplasmic members regulating in essential processes like translation. The predominant ABC protein classification scheme is derived from human members, but the increasing number of fully sequenced genomes permits to reevaluate this paradigm in the light of the evolutionary history the ABC-protein superfamily. As we study the diversity of substrates, mechanisms, and physiological roles of ABC proteins, knowledge of the evolutionary relationships highlights similarities and differences that can be attributed to specific branches in protein divergence. While alignments and trees built on natural sequence variation account for the evolutionary divergence of ABC proteins, high-throughput experiments and next-generation sequencing creating experimental sequence variation are instrumental in identifying functional constraints. The combination of natural and experimentally produced sequence variation allows a broader and more rational study of the function and physiological roles of ABC proteins.

Regulation of dynamic pigment cell states at single-cell resolution

Cells bearing pigment have diverse roles and are often under strict evolutionary selection. Here, we explore the regulation of pigmented cells in the purple sea urchin Strongylocentrotus purpuratus, an emerging model for diverse pigment function. We took advantage of single cell RNA-seq (scRNAseq) technology and discovered that pigment cells in the embryo segregated into two distinct populations, a mitotic cluster and a post-mitotic cluster. Gcm is essential for expression of several genes important for pigment function, but is only transiently expressed in these cells. We discovered unique genes expressed by pigment cells and test their expression with double fluorescence in situ hybridization. These genes include new members of the fmo family that are expressed selectively in pigment cells of the embryonic and in the coelomic cells of the adult - both cell-types having immune functions. Overall, this study identifies nodes of molecular intersection ripe for change by selective evolutionary pressures.

Iron metabolic pathways in the processes of sponge plasticity

The ability to regulate oxygen consumption evolved in ancestral animals and is intrinsically linked to iron metabolism. The iron pathways have been intensively studied in mammals, whereas data on distant invertebrates are limited. Sea sponges represent the oldest animal phylum and have unique structural plasticity and capacity to reaggregate after complete dissociation. We studied iron metabolic factors and their expression during reaggregation in the White Sea cold-water sponges Halichondria panicea and Halisarca dujardini. De novo transcriptomes were assembled using RNA-Seq data, and evolutionary trends were analyzed with bioinformatic tools. Differential expression during reaggregation was studied for H. dujardini. Enzymes of the heme biosynthesis pathway and transport globins, neuroglobin (NGB) and androglobin (ADGB), were identified in sponges. The globins mutate at higher evolutionary rates than the heme synthesis enzymes. Highly conserved iron-regulatory protein 1 (IRP1) presumably interacts with the iron-responsive elements (IREs) found in mRNAs of ferritin (FTH1) and a putative transferrin receptor NAALAD2. The reaggregation process is accompanied by increased expression of IRP1, the antiapoptotic factor BCL2, the inflammation factor NFκB (p65), FTH1 and NGB, as well as by an increase in mitochondrial density. Our data indicate a complex mechanism of iron regulation in sponge structural plasticity and help to better understand general mechanisms of morphogenetic processes in multicellular species.

Simvastatin affect the expression of detoxification-related genes and enzymes in Daphnia magna and alter its life history parameters

Simvastatin (SV), as an hypocholesterolaemic drug, has been detected in various aquatic environment. However, limited information is available on the effects of SV on freshwater invertebrates. In the present study, we investigated the toxic effects of SV on Daphnia. magna (D. magna) through measuring the physiological changes (e.g., survival, growth rate, and reproduction) in a 21-d chronic toxicity test We also determined the expression of seven detoxification and reproduction-related genes (i.e. HR96, P-gp, CYP360A8, GST, CYP314, EcR and Vtg) and several enzymes (i.e. APND, ERND, GST and CAT) in a acute test (24 h). Results showed that high concentration (e.g. 50 μg L^-1) of SV for short time exposure (e.g. 24 h) significantly induced the expression of HR96 and P-gp (e.g. up to 2.5 folds)and enzymes (e.g. increasing 4.0 folds for ERND and GST activity) in D. magna.. The long-term chronic exposure (21 days) may cause the changes of life history parameters such as decreasing total egg production number per individual and intrinsic growth rates etc. SV may act as a potential endocrine disruptor to D. magna and the reproduction parameters were more sensitive endpoints than the survival and growth for evaluating SV exposure.

Studies of the effects of microplastics on aquatic organisms: What do we know and where should we focus our efforts in the future?

The effects of microplastics (MP) on aquatic organisms are currently the subject of intense research. Here, we provide a critical perspective on published studies of MP ingestion by aquatic biota. We summarize the available research on MP presence, behaviour and effects on aquatic organisms monitored in the field and on laboratory studies of the ecotoxicological consequences of MP ingestion. We consider MP polymer type, shape, size as well as group of organisms studied and type of effect reported. Specifically, we evaluate whether or not the available laboratory studies of MP are representative of the types of MPs found in the environment and whether or not they have reported on relevant groups or organisms. Analysis of the available data revealed that 1) despite their widespread detection in field-based studies, polypropylene, polyester and polyamide particles were under-represented in laboratory studies; 2) fibres and fragments (800-1600 μm) are the most common form of MPs reported in animals collected from the field; 3) to date, most studies have been conducted on fish; knowledge is needed about the effects of MPs on other groups of organisms, especially invertebrates. Furthermore, there are significant mismatches between the types of MP most commonly found in the environment or reported in field studies and those used in laboratory experiments. Finally, there is an overarching need to understand the mechanism of action and ecotoxicological effects of environmentally relevant concentrations of MPs on aquatic organism health.

The protective role of multixenobiotic resistance (MXR)-mediated ATP-binding cassette (ABC) transporters in biocides-exposed rotifer Brachionus koreanus

P-glycoprotein (P-gp) and multidrug resistance-associated protein (MRP) are ATP-binding cassette (ABC) transporters that confer multixenobiotic resistance (MXR) via their efflux activity, which enables a variety of xenobiotics to be expelled from cells. MXR has been proposed as the first line of defense against xenobiotics. In this study, the protective roles of P-gp and MRP in the rotifer Brachionus koreanus were examined in response to four biocides (alachlor, chlorpyrifos, endosulfan, and molinate) using fluorescent substrates and inhibitors specific to P-gp and MRP. Exposure of rotifers to the four biocides resulted in increased P-gp and MRP activity. Moreover, the rotifers became more sensitive to the biocides with a reduced tendency in survival and slower population growth rates, when P-gp or MRP was inhibited. These findings suggest that P-gp and MRP are involved in the defense system in response to biocide exposure. Furthermore, the transcriptional levels of the genes encoding P-gp and MRP were examined to uncover the mechanism by which MXR is regulated. Our results demonstrate a crucial role of the MXR efflux system in the defense response to biocides, thereby providing a better understanding of rotifer defense mechanisms on the molecular level.

ABCB1 and ABCC1-like transporters in immune system cells from sea urchins Echinometra lucunter and Echinus esculentus and oysters Crassostrea gasar and Crassostrea gigas

ABC transporters activity and expression have been associated with the multixenobiotic resistance phenotype (MXR). The activity of these proteins leads to a reduction in the intracellular concentration of several xenobiotics, thus reducing their toxicity. However, little attention has been given to the expression of ABC transporters in marine invertebrates and few studies have investigated their role in immune system cells of sea urchins and shellfish bivalves. The aim of the present study was to investigate the activity of the ABC transporters ABCB1 and ABCC1 in immune system cells of sea urchins (coelomocytes) and oysters (hemocytes) from different climatic regions (Brazil and France). Sea urchins and oysters were collected at Paraíba coast; Brazil (Echinometra lucunter and Crassostrea gasar) and Rade of Brest; France (Echinus esculentus and Crassostrea gigas). Coelomocytes and hemocytes were stained with the ABC transporter substrate calcein-AM and dye accumulation analyzed under flow cytometry. Reversin 205 (ABCB1 transporter blocker) and MK571 (ABCC1 transporter blocker) were used as pharmacological tools to investigate ABC transporter activity. A different pattern of calcein accumulation was observed in coelomocytes: phagocytes > colorless spherulocytes > vibrate cells > red spherulocytes. The treatment with MK571 increased calcein fluorescence levels in coelomocytes from both species. However, reversin 205 treatment was not able to increase calcein fluorescence in E. esculentus coelomocytes. These data suggest that ABCC1-like transporter activity is present in both sea urchin species, but ABCB1-like transporter activity might only be present in E. lucunter coelomocytes. The activity of ABCC1-like transporter was observed in all cell types from both bivalve species. However, reversin 205 only increased calcein accumulation in hyalinocytes of the oyster C. gasar, suggesting the absence of ABCB1-like transporter activity in all other cell types, including hyalinocytes from the oyster C. gigas. Additionally, our results showed that C. gigas exhibited higher activity of ABCC1-like transporter in all hemocyte types than C. gasar. The present work is the first to characterize ABCB1 and ABCC1-like transporter activity in the immune system cells of sea urchins E. lucunter and E. esculentus and oysters. Our findings encourage the performing studies regarding ABC transporters activity/expression in immune system cells form marine invertebrates under stress conditions and the possible use of ABC transporters as biomarkers.

Investigating appearance and regulation of the MXR phenotype in early embryo stages of the Mediterranean mussel (Mytilus galloprovincialis)

Multixenobiotic resistance (MXR) efflux transporters constitute a broad-spectrum physiological defense system allowing marine bivalves to cope with environmental challenges. There is, however, scarce information on the type and role that different MXR transporters may have in embryos, which represent the most sensitive stages of bivalves to environmental stress. In this study regulation of MXR-related transporters was investigated in early developmental stages of the Mediterranean mussel (Mytilus galloprovincialis). In vitro fertilization experiments using gametes from naturally-spawning broodstocks were performed to follow embryo development from fertilized eggs (30min post fertilization, pf) to fully developed D-shape veligers (48hpf). Quantitative PCR analyses indicated that ABCB and ABCC transcripts encoding the MXR-related transporters P-glycoproteins (P-gp) and Multidrug resistance proteins (Mrp), respectively, were expressed soon after 30minpf, with ABCC being more expressed than ABCB. Copy numbers of both transcripts were increased in trochophorae and D-veligers. MXR efflux activity assessed using the fluorescent substrate rhodamine 123 and selective P-gp or Mrp inhibitors showed that the P-gp mediated efflux was detected only in D-veligers, while a significant Mrp mediated efflux was detected soon after 30minpf and remained almost unchanged in trochophorae and D-veligers. MXR modulation by propranolol and carbamazepine showed that the pharmaceuticals may act as transcriptional regulators and substrates. Results reported lead to hypothesize that while P-gp aids in xenobiotic efflux performing a prominent protective role, Mrp could be a dual-functioning transporter performing both protective and physiological functions in mussel development.

ATP-binding cassette (ABC) proteins in aquatic invertebrates: Evolutionary significance and application in marine ecotoxicology

The ATP-binding cassette (ABC) protein superfamily is known to play a fundamental role in biological processes and is highly conserved across animal taxa. The ABC proteins function as active transporters for multiple substrates across the cellular membrane by ATP hydrolysis. As this superfamily is derived from a common ancestor, ABC genes have evolved via lineage-specific duplications through the process of adaptation. In this review, we summarized information about the ABC gene families in aquatic invertebrates, considering their evolution and putative functions in defense mechanisms. Phylogenetic analysis was conducted to examine the evolutionary significance of ABC gene families in aquatic invertebrates. Particularly, a massive expansion of multixenobiotic resistance (MXR)-mediated efflux transporters was identified in the absence of the ABCG2 (BCRP) gene in Ecdysozoa and Platyzoa, suggesting that a loss of Abcg2 gene occurred sporadically in these species during divergence of Protostome to Lophotrochozoa. Furthermore, in aquatic invertebrates, the ecotoxicological significance of MXR is discussed while considering the role of MXR-mediated efflux transporters in response to various environmental pollutants.

Toxic effects of diclofenac on life history parameters and the expression of detoxification-related genes in Daphnia magna

Diclofenac (DCF), as a widely used drug, has been detected in various environmental media such as municipal wastewater effluent. However, there is little information on the effects of DCF on freshwater invertebrates potentially exposing to its residues in surface water. In the present study, we investigated the toxic effects of DCF on the physiological parameters (e.g., survival, growth rate, and reproduction) of a crustacean, Daphnia magna, via a 21-d chronic toxicity test, and we also evaluated the effects of DCF on the expression of the genes related to the detoxification metabolism, growth, development and reproduction (e.g., HR96, P-gp, CYP360A8, CYP314, GST, EcR and Vtg) in acute exposure (up to 96h) with RT-PCR. Significant toxic effects of DCF to D. magna were observed at 50μgL^-1, the expression of these selected genes was inhibited with 24h of exposure, and induced after 48h to some extents. The expression of Vtg was induced at high concentrations of DCF (500μgL^-1 and 5000μgL^-1) after 24h and 48h of exposure, but also significantly induced at low concentration (50μgL^-1) after 96h of exposure. Dose- and time-dependent relationships were observed for gene expression of the seven selected genes. In the 21-d chronic toxicity test, the days to the first brood and the days to the first egg production were both significantly delayed at 50μgL^-1. However, there were no significant differences observed among the molting frequency, number of eggs produced in the first brood, total number of eggs per individual, total number of broods per individual, body length and intrinsic growth rate. Our results suggested that the reproduction parameters are more sensitive endpoints than the survival and growth for evaluating the toxicity of DCF to aquatic invertebrates.

Inhibition of multixenobiotic resistance transporters (MXR) by silver nanoparticles and ions in vitro and in Daphnia magna

The P-glycoprotein (P-gp, ABCB1) and multidrug resistance associated protein 1 (MRP1), important members of the ABC (ATP-binding cassette) transporters, protect cells and organisms via efflux of xenobiotics and are responsible for the phenomenon of multidrug or multixenobiotic resistance (MXR). In this study we first evaluated, in vitro, the interaction of silver nanoparticles (Ag NPs, 20, 23 and 27nm), Ag 200nm particles and Ag ions (AgNO3) with MXR efflux transporters using MDCKII and the P-gp over-expressing MDCKII-MDR1 cells and calcein-AM as a substrate of the transporters. Next the in vivo modulation of MXR activity was studied in Daphnia magna juveniles with the model P-gp and MRP1 inhibitors verapamil-HCl and MK571, respectively. The common environmental contaminants perfluorooctane sulfonate and bisphenol A, previously observed to interfere with the P-gp in vitro, also inhibited the efflux of calcein in vivo. Small-sized Ag NPs (with biomolecules present on the surface) and AgNO3 inhibited the MXR activity in daphnids and MDCKII-MDR1 cells, but abcb1 gene expression remained unchanged. Both Ag NPs and dissolved ions contributed to the effects. This study provides evidence of the interference of Ag NPs and AgNO3 with the MXR activity both in vitro and in D. magna, and should be taken into account when Ag NP toxicity is assessed.

Insights into the regulation of the MXR response in haemocytes of the Mediterranean mussel (Mytilus galloprovincialis)

This study investigated functional and transcriptional modulation of the Multixenobiotic resistance (MXR) system as a cytoprotective mechanism contributing to the physiological chemoresistance of haemocytes in the Mediterranean mussel. Basal transport activity was assessed using the model substrate rhodamine 123 and specific inhibitors for the MXR-related transporters P-glycoprotein (ABCB mRNA) and Multidrug resistance-related protein (ABCC mRNA). Results showed that MXR activity in mussel haemocytes was mainly supported by the Mrp-mediated efflux. In agreement, ABCC was expressed at higher levels than ABCB. Activation of the cyclic-AMP (cAMP) dependent protein kinase A (PKA) resulted in increased rhodamine efflux, which was counteracted by the selective PKA inhibitor H89. Although serotonin, a physiological modulator of cAMP/PKA signaling and ABCB transcription in haemocytes, did not affect basal MXR transport, the environmental pharmaceuticals fluoxetine, propranolol, and carbamazepine, which interact in different ways with the adrenergic and serotoninergic pathways, were showed to act as modulators and substrates of MXR-related transporters and to affect cell viability. While the increased MXR activity may have lowered the cytotoxic effects of propranolol and carbamazepine, the lack of MXR efflux induction by fluoxetine may play a role in the observed cytotoxicity of the compound.

ABC transporters and xenobiotic defense systems in early life stages of rainbow trout (Oncorhynchus mykiss)

Embryos of oviparous fish, in contrast to (ovo) viviparous species, develop in the aquatic environment, and therefore need solute transport systems at their body surfaces for maintaining internal homeostasis and defending against potentially harmful substances. We hypothesized that solute transporters undergo changes in tissue distribution from the embryo to the larval stage. We therefore studied the mRNA profiles of eight ABC transporters (abcb1a, abcb1b, abcc1, abcc2, abcc3, abcc4, abcc5, abcg2) and three solute carriers (oatp1d, putative oatp2 putative, mate1) in different body regions (head, yolk sac epithelium, abdominal viscera, skin/muscles) of developing rainbow trout. Additionally, we investigated mRNA levels of phase I (cyp1a, cyp3a) and phase II (gstp, putative ugt1, putative ugt2) biotransformation enzymes. The study covered the developmental period from the eleuthero-embryo stage to the first-feeding larval stage (1-20days post-hatch, dph). At 1dph, transcripts of abcc2, abcc4, abcg2, cyp3a, gstp, putative mate1, and putative oatp2 occurred primarily in the yolk sac epithelium, whereas at later stages expression of these genes was predominantly observed in the abdominal viscera. The functional activity of ABC transporters in fish early life stages was assessed by rhodamine B accumulation assays. Finally, we investigated the potential impact of xenobiotics (clotrimazole, clofibric acid) on the ABC and biotransformation systems of trout early life stages. While clofibric acid had no effect, clotrimazole lead to an increased rhodamine B accumulation. The results provide evidence that the transition from the eleuthero-embryo to the larval stage is accompanied by a major alteration in tissue expression of ABC transporters.

Functional diversification of sea urchin ABCC1 (MRP1) by alternative splicing

The multidrug resistance protein (MRP) family encodes a diverse repertoire of ATP-binding cassette (ABC) transporters with multiple roles in development, disease, and homeostasis. Understanding MRP evolution is central to unraveling their roles in these diverse processes. Sea urchins occupy an important phylogenetic position for understanding the evolution of vertebrate proteins and have been an important invertebrate model system for study of ABC transporters. We used phylogenetic analyses to examine the evolution of MRP transporters and functional approaches to identify functional forms of sea urchin MRP1 (also known as SpABCC1). SpABCC1, the only MRP homolog in sea urchins, is co-orthologous to human MRP1, MRP3, and MRP6 (ABCC1, ABCC3, and ABCC6) transporters. However, efflux assays revealed that alternative splicing of exon 22, a region critical for substrate interactions, could diversify functions of sea urchin MRP1. Phylogenetic comparisons also indicate that while MRP1, MRP3, and MRP6 transporters potentially arose from a single transporter in basal deuterostomes, alternative splicing appears to have been the major mode of functional diversification in invertebrates, while duplication may have served a more important role in vertebrates. These results provide a deeper understanding of the evolutionary origins of MRP transporters and the potential mechanisms used to diversify their functions in different groups of animals.

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.

ABCC5 is required for cAMP-mediated hindgut invagination in sea urchin embryos

ATP-binding cassette (ABC) transporters are evolutionarily conserved proteins that pump diverse substrates across membranes. Many are known to efflux signaling molecules and are extensively expressed during development. However, the role of transporters in moving extracellular signals that regulate embryogenesis is largely unexplored. Here, we show that a mesodermal ABCC (MRP) transporter is necessary for endodermal gut morphogenesis in sea urchin embryos. This transporter, Sp-ABCC5a (C5a), is expressed in pigment cells and their precursors, which are a subset of the non-skeletogenic mesoderm (NSM) cells. C5a expression depends on Delta/Notch signaling from skeletogenic mesoderm and is downstream of Gcm in the aboral NSM gene regulatory network. Long-term imaging of development reveals that C5a knockdown embryos gastrulate, but ∼90% develop a prolapse of the hindgut by the late prism stage (∼8 h after C5a protein expression normally peaks). Since C5a orthologs efflux cyclic nucleotides, and cAMP-dependent protein kinase (Sp-CAPK/PKA) is expressed in pigment cells, we examined whether C5a could be involved in gastrulation through cAMP transport. Consistent with this hypothesis, membrane-permeable pCPT-cAMP rescues the prolapse phenotype in C5a knockdown embryos, and causes archenteron hyper-invagination in control embryos. In addition, the cAMP-producing enzyme soluble adenylyl cyclase (sAC) is expressed in pigment cells, and its inhibition impairs gastrulation. Together, our data support a model in which C5a transports sAC-derived cAMP from pigment cells to control late invagination of the hindgut. Little is known about the ancestral functions of ABCC5/MRP5 transporters, and this study reveals a novel role for these proteins in mesoderm-endoderm signaling during embryogenesis.

What do drug transporters really do?

Potential drug-drug interactions mediated by the ATP-binding cassette (ABC) transporter and solute carrier (SLC) transporter families are of clinical and regulatory concern. However, the endogenous functions of these drug transporters are not well understood. Discussed here is evidence for the roles of ABC and SLC transporters in the handling of diverse substrates, including metabolites, antioxidants, signalling molecules, hormones, nutrients and neurotransmitters. It is suggested that these transporters may be part of a larger system of remote communication ('remote sensing and signalling') between cells, organs, body fluid compartments and perhaps even separate organisms. This broader view may help to clarify disease mechanisms, drug-metabolite interactions and drug effects relevant to diabetes, chronic kidney disease, metabolic syndrome, hypertension, gout, liver disease, neuropsychiatric disorders, inflammatory syndromes and organ injury, as well as prenatal and postnatal development.

Effect of bisphenol A on P-glycoprotein-mediated efflux and ultrastructure of the sea urchin embryo

Usage of bisphenol A (BPA) in production of polycarbonate plastics has resulted in global distribution of BPA in the environment. These high concentrations cause numerous negative effects to the aquatic biota, among which the most known is the induction of endocrine disruption. The focus of this research was to determine the effects of two experimentally determined concentrations of BPA (100nM and 4μM) on cellular detoxification mechanisms during the embryonic development (2-cell, pluteus) of the rocky sea urchin (Paracentrotus lividus), primarily the potential involvement of multidrug efflux transport in the BPA intercellular efflux. The results of transport assay, measurements of the intracellular BPA and gene expression surveys, for the first time indicate the importance of P-glycoprotein (P-gp/ABCB1) in defense against BPA. Cytotoxic effects of BPA, validated by the immunohistochemistry (IHC) and the transmission electron microscopy (TEM), induced the aberrant karyokinesis, and consequently, the impairment of embryo development through the first cell division and retardation.

Accumulation and embryotoxicity of polystyrene nanoparticles at early stage of development of sea urchin embryos Paracentrotus lividus

Nanoplastic debris, resulted from runoff and weathering breakdown of macro- and microplastics, represents an emerging concern for marine ecosystems. The aim of the present study was to investigate disposition and toxicity of polystyrene nanoparticles (NPs) in early development of sea urchin embryos (Paracentrotus lividus). NPs with two different surface charges where chosen, carboxylated (PS-COOH) and amine (PS-NH2) polystyrene, the latter being a less common variant, known to induce cell death in several in vitro cell systems. NPs stability in natural seawater (NSW) was measured while disposition and embryotoxicity were monitored within 48 h of postfertilization (hpf). Modulation of genes involved in cellular stress response (cas8, 14-3-3ε, p-38 MAPK, Abcb1, Abcc5) was investigated. PS-COOH forms microaggregates (PDI > 0.4) in NSW, whereas PS-NH2 results are better dispersed (89 ± 2 nm) initially, though they also aggregated partially with time. Their respectively anionic and cationic nature was confirmed by ζ-potential measurements. No embryotoxicity was observed for PS-COOH up to 50 μg mL(-1) whereas PS-NH2 caused severe developmental defects (EC50 3.85 μg mL(-1) 24 hpf and EC50 2.61 μg mL(-1) 48 hpf). PS-COOH accumulated inside embryo's digestive tract while PS-NH2 were more dispersed. Abcb1 gene resulted up-regulated at 48 hpf by PS-COOH whereas PS-NH2 induced cas8 gene at 24 hpf, suggesting an apoptotic pathway. In line with the results obtained with the same PS NPs in several human cell lines, also in sea urchin embryos, differences in surface charges and aggregation in seawater strongly affect their embryotoxicity.

Transport in technicolor: mapping ATP-binding cassette transporters in sea urchin embryos

One quarter of eukaryotic genes encode membrane proteins. These include nearly 1,000 transporters that translocate nutrients, signaling molecules, and xenobiotics across membranes. While it is well appreciated that membrane transport is critical for development, the specific roles of many transporters have remained cryptic, in part because of their abundance and the diversity of their substrates. Multidrug resistance ATP-binding cassette (ABC) efflux transporters are one example of cryptic membrane proteins. Although most organisms utilize these ABC transporters during embryonic development, many of these transporters have broad substrate specificity, and their developmental functions remain incompletely understood. Here, we review advances in our understanding of ABC transporters in sea urchin embryos, and methods developed to spatially and temporally map these proteins. These studies reveal that multifunctional transporters are required for signaling, homeostasis, and protection of the embryo, and shed light on how they are integrated into ancestral developmental pathways recapitulated in disease.

The biology of the germ line in echinoderms

The formation of the germ line in an embryo marks a fresh round of reproductive potential. The developmental stage and location within the embryo where the primordial germ cells (PGCs) form, however, differs markedly among species. In many animals, the germ line is formed by an inherited mechanism, in which molecules made and selectively partitioned within the oocyte drive the early development of cells that acquire this material to a germ-line fate. In contrast, the germ line of other animals is fated by an inductive mechanism that involves signaling between cells that directs this specialized fate. In this review, we explore the mechanisms of germ-line determination in echinoderms, an early-branching sister group to the chordates. One member of the phylum, sea urchins, appears to use an inherited mechanism of germ-line formation, whereas their relatives, the sea stars, appear to use an inductive mechanism. We first integrate the experimental results currently available for germ-line determination in the sea urchin, for which considerable new information is available, and then broaden the investigation to the lesser-known mechanisms in sea stars and other echinoderms. Even with this limited insight, it appears that sea stars, and perhaps the majority of the echinoderm taxon, rely on inductive mechanisms for germ-line fate determination. This enables a strongly contrasted picture for germ-line determination in this phylum, but one for which transitions between different modes of germ-line determination might now be experimentally addressed.

The multi-xenobiotic resistance (MXR) efflux activity in hemocytes of Mytilus edulis is mediated by an ATP binding cassette transporter of class C (ABCC) principally inducible in eosinophilic granulocytes

In marine and estuarine species, immunotoxic and/or immunomodulatory mechanisms are the crossroad of interactions between xenobiotics, microorganisms and physicochemical variations of the environment. In mussels, immunity relies exclusively on innate responses carried out by cells collectively called hemocytes and found in the open hemolymphatic circulatory system of these organisms. However, hemocytes do not form a homogenous population of immune cells since distinct subtypes of mussel blood cells can be distinguished by cytochemistry, flow cytometry or cell motility analysis. Previous studies have also shown that these cells are able to efflux xenobiotics by means of ATP binding cassette (ABC) transporter activities conferring a multixenobiotic resistance (MXR) phenotype. ABC transporters corresponding to vertebrate class B/P-glycoprotein (P-gp) and to class C/multidrug resistance related protein (MRP) are characterized in Mytilidae. Herein, we have investigated the relative contributions of ABCB- and ABCC-mediated efflux within the different hemocyte subpopulations of Mytilus edulis mussels, collected from areas differentially impacted by chemical contaminants in Normandy (France). RT-PCR analyses provide evidence for the presence of ABCB and ABCC transporters transcripts in hemocytes. Immunodetection of ABCB/P-gp with the monoclonal antibody UIC2 in living hemocytes revealed that expression was restricted to granular structures of spread cells. Efflux transporter activities, with calcein-AM as fluorescent probe, were measured by combining flow cytometry to accurate Coulter cell size measurements in order to get a cell-volume normalized fluorescence concentration. In these conditions, basal fluorescence levels were higher in hemocytes originating from Yport (control site) than in cells collected from the harbor of Le Havre, where mussels are more exposed to with persistent pollutants. By using specific ABCB/P-gp (verapamil, PSC833, zosuquidar) and ABCC/MRP (MK571) blockers, we show that MXR activity is only carried out by MRP-type transporters in M. edulis hemocytes. In addition, cell-type-gated flow cytometry and calculation of the MXR activity factor indicate that ABCC-efflux activity is higher and more inducible in eosinophilic granulocytes than in other hemocyte subtypes. We conclude that, in the hemocytes of M. edulis, MXR phenotype is mediated by an ABCC/MRP-type transporter activity principally supported by eosinophilic granulocytes. A role for ABC transporters in hemocyte migration is discussed.

Molecular response to toxic diatom-derived aldehydes in the sea urchin Paracentrotus lividus

Diatoms are dominant photosynthetic organisms in the world’s oceans and represent a major food source for zooplankton and benthic filter-feeders. However, their beneficial role in sustaining marine food webs has been challenged after the discovery that they produce secondary metabolites, such as polyunsaturated aldehydes (PUAs), which negatively affect the reproductive success of many invertebrates. Here, we report the effects of two common diatom PUAs, heptadienal and octadienal, which have never been tested before at the molecular level, using the sea urchin, Paracentrotus lividus, as a model organism. We show that both PUAs are able to induce teratogenesis (i.e., malformations), as already reported for decadienal, the better-studied PUA of this group. Moreover, post-recovery experiments show that embryos can recover after treatment with all three PUAs, indicating that negative effects depend both on PUA concentrations and the exposure time of the embryos to these metabolites. We also identify the time range during which PUAs exert the greatest effect on sea urchin embryogenesis. Finally, we report the expression levels of thirty one genes (having a key role in a broad range of functional responses, such as stress, development, differentiation, skeletogenesis and detoxification processes) in order to identify the common targets affected by PUAs and their correlation with morphological abnormalities. This study opens new perspectives for understanding how marine organisms afford protection from environmental toxicants through an integrated network of genes.

Differential ABCB and ABCC gene expression and efflux activities in gills and hemocytes of Mytilus galloprovincialis and their involvement in cadmium response

The aim of the study was to characterize ABC transport proteins gene expression and efflux activities in gills and hemocytes of the Mediterranean mussel and to evaluate their response to Cd. At basal level a higher expression of abcb-like gene was observed in gills than in hemocytes while abcc-like gene showed similar levels. Both P-gp and MRPs inhibitors (cyclosporine and MK571) blocked efflux activities in gills; hemocytes were sensitive only to MK571. After 120 min in vitro pre-exposure to CdCl2, the efflux activity increased significantly in gills and hemocytes. In vivo exposure to CdCl2 (0.4 μM) increased abcb-like gene expression in gills without affecting efflux activity. In hemocytes abcc-like gene resulted up-regulated and Ca-AM efflux resulted enhanced. An increased uptake of Cd in gills biopsies was observed in the presence of both P-gp and MRPs inhibitors. Our results indicate that ABC transporters seem involved in the first protective response to Cd and this response is tissue-specific.

ATP-binding cassette transporters protect sea urchin gametes and embryonic cells against the harmful effects of ultraviolet light

Embryos of marine organisms whose development occurs externally are particularly sensitive to ultraviolet (UV) light (bands A and B, respectively, UVA and UVB). ATP-binding cassette (ABC) transporters are the first line of cellular defense against chemical or physical stress. The present work investigated the involvement of ABC transporters on UVA or UVB effects on eggs, spermatozoa, and embryonic cells of the sea urchin Echinometra lucunter. Gametes or embryos were exposed to UVA (3.6-14.4 kJ m(-2)) or UVB (0.112-14.4 kJ m(-2)), and embryonic development was monitored by optical microscopy at different developmental stages in the presence or absence of the ABC-transporter blockers reversin205 (ABCB1 blocker) or MK571 (ABCC1 blocker). E. lucunter eggs, spermatozoa and embryos were resistant to UVA exposure. Resistance to the harmful effects of UVB was strongly associated to ABC transporter activity (embryos > eggs > spermatozoa). ABCB1 or ABCC1 blockage promoted the injurious effects of UVA on spermatozoa. ABCC1 transporter blockage increased UVB-dependent damage in eggs while ABCB1 transporter inhibition increased harmful effects of UVB in embryonic cells. ABC-transporter activity was not, however, affected by UVB exposure. In conclusion, the present study is the first report on the protective role of ABC transporters against harmful effects of UVA and UVB on sea urchin eggs and embryonic cells.

Quantification and in situ localisation of abcb1 and abcc9genes in toxicant-exposed sea urchin embryos

A multixenobiotic resistance (MXR) mechanism mediated by ABC binding cassette (ABC) transport proteins is an efficient chemical defence mechanism in sea urchin embryos. The aim of our work was to evidence whether exposure to sub-lethal doses of specific contaminants (oxybenzone (OXI), mercuric chloride (HgCl2) and trybutiltin (TBT)) would induce MXR transporter activity during embryonic development (from zygote to blastula stage) in purple sea urchin (Paracentrotus lividus) embryos. Further, we present data on molecular identification, transport function, expression levels and gene localisation of two ABC efflux transporters-P-glycoprotein (ABCB1/P-gp) and sulfonylurea-receptor-like protein (ABCC9/SUR-like). Partial cDNA sequences of abcb1 and abcc9 were identified and quantitative PCR (qPCR) evidenced an increase in mRNA transcript levels of both ABC transporters during the two-cell, as well as an overall decrease during the blastulae stage. Calcein-AM efflux activity assay indicated the activation of multidrug resistance-associated protein/ABCC-like transport in the presence of HgCl2 and TBT in exposed blastulae. The in situ hybridisation of the two-cell and blastula stages showed ubiquitous localisation of both transcripts within cells, supporting qPCR data. In conclusion, ABCB1 and ABCC9 are constitutive, as are HgCl2, TBT and OXI-inducible ABC membrane transporters, coexpressed in the zygote, two-cell and blastula stages of the P. lividus. Their ubiquitous cell localisation further fortifies their protective role in early embryonic development.

Identification of ABC transporter genes in gonad tissue of two Mediterranean sea urchin species: black, Arbacia lixula L., and rocky, Paracentrotus lividus L

Multixenobiotic resistance (MXR) represents an important cellular detoxification mechanism in aquatic organisms as it provides them robustness toward natural and man-made contaminants. Several ABC transporters have major roles in the MXR phenotype - P-gp/ABCB1, MRP1-3/ABCC1-3 and BCRP/ABCG2. In this study, we identified the presence of ABC transporters involved in the MXR mechanism of Arbacia lixula and Paracentrotus lividus. AlABCB1/P-gp, AlABCC3/MRP3, AlABCC9/SUR-like and AlABCG-like transcripts were identified in A. lixula; and PlABCC1/P-gp, PlABCC3/MRP3, PlABCC5/MRP5, and PlABCC9/SUR-like transcripts in P. lividus. For each of the new partial sequences, we performed detailed phylogenetic and identity analysis as a first step toward full characterization and understanding of the ecotoxicological role of these ABC transporters.

Localization and substrate selectivity of sea urchin multidrug (MDR) efflux transporters

In this study, we cloned, expressed and functionally characterized Stronglycentrotus purpuratus (Sp) ATP-binding cassette (ABC) transporters. This screen identified three multidrug resistance (MDR) transporters with functional homology to the major types of MDR transporters found in humans. When overexpressed in embryos, the apical transporters Sp-ABCB1a, ABCB4a, and ABCG2a can account for as much as 87% of the observed efflux activity, providing a robust assay for their substrate selectivity. Using this assay, we found that sea urchin MDR transporters export canonical MDR susbtrates such as calcein-AM, bodipy-verapamil, bodipy-vinblastine, and mitoxantrone. In addition, we characterized the impact of nonconservative substitutions in the primary sequences of drug binding domains of sea urchin versus murine ABCB1 by mutation of Sp-ABCB1a and treatment of embryos with stereoisomeric cyclic peptide inhibitors (QZ59 compounds). The results indicated that two substitutions in transmembrane helix 6 reverse stereoselectivity of Sp-ABCB1a for QZ59 enantiomers compared with mouse ABCB1a. This suggests that subtle changes in the primary sequence of transporter drug binding domains could fine-tune substrate specificity through evolution.

Inhibition of cellular efflux pumps involved in multi xenobiotic resistance (MXR) in echinoid larvae as a possible mode of action for increased ecotoxicological risk of mixtures

In marine organisms the multi xenobiotic resistance (MXR) mechanism via e.g. P-glycoprotein (P-gp) and multidrug resistance-associated protein (MRP) is an important first line of defense against contaminants by pumping contaminants out of the cells. If compounds would impair the MXR mechanism, this could result in increased intracellular levels of other compounds, thereby potentiating their toxicity. A calcein-AM based larval cellular efflux pump inhibition assay (CEPIA) was developed for echinoid (Psammechinus miliaris) larvae and applied for several contaminants. The larval CEPIA revealed that triclosan (TCS) and the nanoparticles P-85(®) (P-85) were 124 and 155× more potent inhibitors (IC(50) 0.5 ± 0.05 and 0.4 ± 0.1 μM, respectively) of efflux pumps than the model inhibitor Verapamil (VER). PFOS (heptadecafluorooctane sulfonic acid) and pentachlorophenol also were more potent than VER, 24 and 5×, respectively. Bisphenol A and o,p'-dichlorodiphenyltrichloroethane (o,p'-DDT) inhibited efflux pumps with a potency 3× greater than VER. In a 48 h early life stage bioassay with P. miliaris, exposure to a non-lethal concentration of the inhibitors TCS, VER, the model MRP inhibitor MK-571, the nanoparticles P-85 and the model P-gp inhibitor PSC-833, increased the toxicity of the toxic model substrate for efflux pumps vinblastine by a factor of 2, 4, 4, 8 and 16, respectively. Our findings show that several contaminants accumulating in the marine environment inhibit cellular efflux pumps, which could potentiate toxic effects of efflux pumps substrates.

Involvement of ABCB1 and ABCC1 transporters in sea urchin Echinometra lucunter fertilization

Fertilization is an ordered sequence of cellular interactions that promotes gamete fusion to form a new individual. Since the pioneering work of Oskar Hertwig conducted on sea urchins, echinoderms have contributed to the understanding of cellular and molecular aspects of the fertilization processes. Studies on sea urchin spermatozoa reported the involvement of a plasma membrane protein that belongs to the ABC proteins superfamily in the acrosome reaction. ABC transporters are expressed in membranes of eukaryotic and prokaryotic cells, and are associated with the transport of several compounds or ions across biomembranes. We aimed to investigate ABCB1 and ABCC1 transporter activity in sea urchin spermatozoa and their involvement in fertilization. Our results indicate that Echinometra lucunter spermatozoa exhibit a low intracellular calcein accumulation (18.5% stained cells); however, the ABC blockers reversin205, verapamil, and MK571 increased dye accumulation (93.0-96.6% stained cells). We also demonstrated that pharmacologically blocking ABCB1 and ABCC1 decreased spermatozoa fertilizing capacity (70% inhibition), and this phenotype was independent of extracellular calcium. These data suggest that functional spermatozoa ABCB1 and ABCC1 transporters are crucial for a successful fertilization. Additional studies must be performed to investigate the involvement of membrane lipid homeostasis in the fertilization process.

Cyclic nucleotide compartmentalization: contributions of phosphodiesterases and ATP-binding cassette transporters

Cyclic nucleotides [e.g., cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP)] are ubiquitous second messengers that affect multiple cell functions from maturation of the egg to cell division, growth, differentiation, and death. The concentration of cAMP can be regulated by processes within membrane domains (local regulation) as well as throughout a cell (global regulation). The phosphodiesterases (PDEs) that degrade cAMP have well-known roles in both these processes. It has recently been discovered that ATP-binding cassette (ABC) transporters contribute to both local and global regulation of cAMP. This regulation may require the formation of macromolecular complexes. Some of these transporters are ubiquitously expressed, whereas others are more tissue restricted. Because some PDE inhibitors are also ABC transporter inhibitors, it is conceivable that the therapeutic benefits of their use result from the combined inhibition of both PDEs and ABC transporters. Deciphering the individual contributions of PDEs and ABC transporters to such drug effects may lead to improved therapeutic benefits.

Actin polymerization controls the activation of multidrug efflux at fertilization by translocation and fine-scale positioning of ABCB1 on microvilli

Multidrug efflux is activated at fertilization in sea urchin eggs, but it is unclear how cortical reorganization initiates transport. Using structured illumination microscopy, we found that the multidrug transporter ABCB1a translocates along polymerizing actin filaments to the microvillar tips. This short-range (micrometer scale) translocation is necessary for up-regulation of efflux activity.

Fertilization changes the structure and function of the cell surface. In sea urchins, these changes include polymerization of cortical actin and a coincident, switch-like increase in the activity of the multidrug efflux transporter ABCB1a. However, it is not clear how cortical reorganization leads to changes in membrane transport physiology. In this study, we used three-dimensional superresolution fluorescence microscopy to resolve the fine-scale movements of the transporter along polymerizing actin filaments, and we show that efflux activity is established after ABCB1a translocates to the tips of the microvilli. Inhibition of actin poly­merization or bundle formation prevents tip localization, resulting in the patching of ABCB1a at the cell surface and decreased efflux activity. In contrast, enhanced actin polymerization promotes tip localization. Finally, interference with Rab11, a regulator of apical recycling, inhibits activation of efflux activity in embryos. Together our results show that actin-mediated, short-range traffic and positioning of transporters at the cell surface regulates multidrug efflux activity and highlight the multifaceted roles of microvilli in the spatial distribution of membrane proteins.