Marine invertebrate cytochrome P450: emerging insights from vertebrate and insects analogies

Cytochrome P450 enzymes (P450s) are responsible for the oxidative metabolism of a plethora of endogenous and exogenous substrates. P450s and associated activities have been demonstrated in numerous marine invertebrates belonging to the phyla Cnidaria, Annelida (Polychaeta), Mollusca, Arthropoda (Crustacea) and Echinodermata. P450s of marine invertebrates and vertebrates show considerable sequence divergence and the few orthologs reveal the selective constraint on physiologically significant enzymes. P450s are present in virtually all tissues of marine invertebrates, although high levels usually are found in hepatic-like organs and steroidogenic tissues. High-throughput technologies result in the rapid acquisition of new marine invertebrate P450 sequences; however, the understanding of their function is poor. Based on analogy to vertebrates and insects, it is likely that P450s play a pivotal role in the physiology of marine invertebrates by catalyzing the biosynthesis of signal molecules including steroids such as 20-hydroxyecdysone (the molting hormone of crustaceans). The metabolism of many exogenous compounds including benzo(a)pyrene (BaP), pyrene, ethoxyresorufin, ethoxycoumarin and aniline is mediated by P450 enzymes in tissues of marine invertebrates. P450 gene expression, protein levels and P450 mediated metabolism of xenobiotics are induced by PAHs in some marine invertebrate species. Thus, regulation of P450 enzyme activity may play a central role in the adaptation of animals to environmental pollutants. Emphasis should be put on the elucidation of the function and regulation of the ever-increasing number of marine invertebrate P450s.     

The effects of the stress response on immune function in invertebrates: An evolutionary perspective on an ancient connection

This article is part of a Special Issue "Neuroendocrine-Immune Axis in Health and Disease." Stress-induced changes in immune function occur in animals across phyla, and these effects are usually immunosuppressive. The function of this immunomodulation remains elusive; however, the existence of specialized receptors on immune cells suggests that it is adaptive. A comparative approach may provide a useful perspective. Although invertebrates have simpler endocrine/neuroendocrine systems and immune systems than vertebrates, they have robust stress responses that include the release of stress hormones/neurohormones. Stress hormones modify immune function in mollusks, insects, and crustaceans. As in vertebrates, the effects of stress hormones/neurohormones on invertebrate immune function are complex, and are not always immunosuppressive. They are context-, stressor-, time- and concentration-dependent. Stress hormone effects on invertebrate immune function may help to re-align resources during fight-or-flight behavior. The data are consistent with the hypothesis that stress hormones induce a reconfiguration of networks at molecular, cellular and physiological levels that allow the animal to maintain optimal immunity as the internal environment changes. This reconfiguration enhances some immune functions while suppressing others. Knowing the molecular details of these shifts will be critical for understanding the adaptive function of stress hormones on immune function.     

环境污染对几类水生无脊椎动物内分泌功能扰乱的研究现状

近年来，在环境毒理学这门边缘学科中又诞生了一个新的领域，即环境污染对内分泌功能的扰乱。研究发现，许多人工合成的杀虫剂和工业化合物能够扰乱脊椎动物的内分泌功能，这些化合物也存在于水环境中。近年来，这些环境有机污染物是否对水生无脊椎动物的内分泌功能同样具有扰乱作用成了环境内分泌学这个新领域的热点之一。由于近年来的研究侧重于腔肠动物、轮虫、软体动物、甲壳动物及棘皮动物，因此，本文主要介绍有关环境污染物对这几类水生无脊椎动物内分泌功能扰乱的研究进展。另外，对环境污染对水生无脊椎动物内分泌扰乱这个研究热点的现状以及今后的发展方向进行了评述。在从事环境污染对无脊椎动物内分泌功能影响的研究时，研究者必须意识到无脊椎动物和脊椎动物在内分泌机制上的差异，不可随意地在这两大类动物类群之间互相引伸研究结果。     

Endocrine disruptors in marine organisms: approaches and perspectives

Organic pollutants exhibiting endocrine disrupting activity (Endocrine Disruptors--EDs) are prevalent over a wide range in the aquatic ecosystems; most EDs are resistant to environmental degradation and are considered ubiquitous contaminants. The actual potency of EDs is low compared to that of natural hormones, but environmental concentrations may still be sufficiently high to produce detrimental biological effects. Most information on the biological effects and mechanisms of action of EDs has been focused on vertebrates. Here we summarize recent progress in studies on selected aspects of endocrine disruption in marine organisms that are still poorly understood and that certainly deserve further research in the near future. This review, divided in four sections, focuses mainly on invertebrates (effects of EDs and mechanisms of action) and presents data on top predators (large pelagic fish and cetaceans), a group of vertebrates that are particularly at risk due to their position in the food chain. The first section deals with basic pathways of steroid biosynthesis and metabolism as a target for endocrine disruption in invertebrates. In the second section, data on the effects and alternative mechanisms of action of estrogenic compounds in mussel immunocytes are presented, addressing to the importance of investigating full range responses to estrogenic chemicals in ecologically relevant invertebrate species. In the third section we review the potential use of vitellogenin (Vtg)-like proteins as a biomarker of endocrine disruption in marine bivalve molluscs, used worldwide as sentinels in marine biomonitoring programmes. Finally, we summarize the results of a recent survey on ED accumulation and effects on marine fish and mammals, utilizing both classical biomarkers of endocrine disruption in vertebrates and non-lethal techniques, such as non-destructive biomarkers, indicating the toxicological risk for top predator species in the Mediterranean. Overall, the reviewed data underline the potential to identify specific types of responses to specific groups of chemicals such as EDs in order to develop suitable biomarkers that could be useful as diagnostic tools for endocrine disruption in marine invertebrates and vertebrates.     

A critical analysis of the biological impacts of plasticizers on wildlife

This review provides a critical analysis of the biological effects of the most widely used plasticizers, including dibutyl phthalate, diethylhexyl phthalate, dimethyl phthalate, butyl benzyl phthalate and bisphenol A (BPA), on wildlife, with a focus on annelids (both aquatic and terrestrial), molluscs, crustaceans, insects, fish and amphibians. Moreover, the paper provides novel data on the biological effects of some of these plasticizers in invertebrates, fish and amphibians. Phthalates and BPA have been shown to affect reproduction in all studied animal groups, to impair development in crustaceans and amphibians and to induce genetic aberrations. Molluscs, crustaceans and amphibians appear to be especially sensitive to these compounds, and biological effects are observed at environmentally relevant exposures in the low ng l⁻¹ to µg l⁻¹ range. In contrast, most effects in fish (except for disturbance in spermatogenesis) occur at higher concentrations. Most plasticizers appear to act by interfering with the functioning of various hormone systems, but some phthalates have wider pathways of disruption. Effect concentrations of plasticizers in laboratory experiments coincide with measured environmental concentrations, and thus there is a very real potential for effects of these chemicals on some wildlife populations. The most striking gaps in our current knowledge on the impacts of plasticizers on wildlife are the lack of data for long-term exposures to environmentally relevant concentrations and their ecotoxicity when part of complex mixtures. Furthermore, the hazard of plasticizers has been investigated in annelids, molluscs and arthropods only, and given the sensitivity of some invertebrates, effects assessments are warranted in other invertebrate phyla.     

Photoreception in Marine Invertebrates

SYNOPSIS. In order for photoperiodic phenomena to be expressedby any animal, the organism must possess some sort of photoreceptor.This may be in the form of an eye or an extraocular receptor,and the invertebrate phyla illustrate fantastic diversity indesign of either receptor type. While all the major invertebratephyla possess photoreceptor organs of one type or another, thebest-studied groups are those with highly complex eyes. Theseinclude the crustaceans, the molluscs, and some polychaete annelids.Many species in these groups possess eyes having extreme sensitivity,good spatial resolution, and in some cases multiple spectralchannels. In a few taxa, the eyes are known to provide inputto circadian oscillators, which suggests that they may alsobe employed for measurement of photoperiod. Extraocular photoreceptorsinclude dermal and ganglionic sense organs, which also feedinto circadian systems in numerous invertebrates, from cnidariansto molluscs and arthropods.     

Tachykinin-related peptides in invertebrates: a review

Peptides with sequence similarities to members of the tachykinin family have been identified in a number of invertebrates belonging to the mollusca, echiuridea, insecta and crustacea. These peptides have been designated tachykinin-related peptides (TRPs) and are characterized by the preserved C-terminal pentapeptide FX1GX2Ramide (X1 and X2 are variable residues). All invertebrate TRPs are myostimulatory on insect hindgut muscle, but also have a variety of additional actions: they can induce contractions in cockroach foregut and oviduct and in moth heart muscle, trigger a motor rhythm in the crab stomatogastric ganglion, depolarize or hyperpolarize identified interneurons of locust and the snail Helix and induce release of adipokinetic hormone from the locust corpora cardiaca. Two putative TRP receptors have been cloned from Drosophila; both are G-protein coupled and expressed in the nervous system. The invertebrate TRPs are distributed in interneurons of the CNS of Limulus, crustaceans and insects. In the latter two groups TRPs are also present in the stomatogastric nervous system and in insects endocrine cells of the midgut display TRP-immunoreactivity. In arthropods the distribution of TRPs in neuronal processes of the brain displays similar patterns. Also in coelenterates, flatworms and molluscs TRPs have been demonstrated in neurons. The activity of different TRPs has been explored in several assays and it appears that an amidated C-terminal hexapeptide (or longer) is required for bioactivity. In many invertebrate assays the first generation substance P antagonist spantide I is a potent antagonist of invertebrate TRPs and substance P. Locustatachykinins stimulate adenylate cyclase in locust interneurons and glandular cells of the corpora cardiaca, but in other tissues the putative second messenger systems have not yet been identified. The heterologously expressed Drosophila TRP receptors coupled to the phospholipase C pathway and could induce elevations of inositol triphosphate. The structures, distributions and actions of TRPs in various invertebrates are compared and it is concluded that the TRPs are multifunctional peptides with targets both in the central and peripheral nervous system and other tissues, similar to vertebrate tachykinins. Invertebrate TRPs may also be involved in developmental processes.     

A comparative study of high molecular weight proteins in various types of muscle across the animal kingdom

A wide range of phyla have been surveyed by SDS-PAGE for the new large proteins of the myofibril. Connectin (or titin) appears to be widely distributed. It is seen as a band of constant intensity and mobility in vertebrate striated muscle, but is absent from smooth muscle. It appears in more variable amounts, in a form of constant but greater mobility in many invertebrates: worms, molluscs (adductor but not gastropod feet), insects, a myriapod, and even in human blood platelets. Nebulin shares the same distribution in vertebrate muscles except for its notable absence in all heart muscle examined. It too is found in many invertebrates, not always with titin. It has been found in a worm, molluscs (adductor and gastropod feet), insects, crustaceans and an echinoderm. The mobility of nebulin varies within the vertebrates and more so between invertebrates (where, as with titin, it is greater). The isoforms of filamin in skeletal, cardiac, and smooth muscles of vertebrates are recorded. C-protein in rabbit muscles has four isoforms: white, alpha-red (X-protein), beta-red, and cardiac.     

Evolutionary aspects of octopaminergic systems with emphasis on arthropods

We review current knowledge on octopaminergic systems in all major phyla with emphasis on arthropods. Octopaminergic systems occur in all triploblastic animals investigated. Close relationships of the octopamine-receptors in protostomes to vertebrate alpha-adrenergic receptors suggest an ancient common origin. Some evidence suggests that the octopaminergic system may be younger than the vertebrate adrenergic system. All octopaminergic systems are constructed from comparatively few neurons, and the cell populations in different representatives of a given phylum are clearly similar. Current data do not allow any conclusions on the relationships between molluscs and annelids (Lophotrochozoa) to nematodes and arthropods (Ecdysozoa).In chelicerates, including Limulus as a remaining xiphosuran, and crustaceans, octopaminergic neurons occur in pairs. All investigated winged insects (Pterygota) possess similar arrangements of octopaminergic cell populations, suggesting that their octopaminergic systems have been largely conserved during evolution. Unpaired octopaminergic neurons, with symmetrical, bilaterally projecting efferent axons in insects do not appear to have counterparts in other arthropods. Unpaired-octopaminergic neurons may thus be an autapomorphic feature of winged insects. Octopamine acts as an inhibitory neurotransmitter in gastropods, and as an excitatory transmitter controlling bioluminescence in fireflies. Octopamine is also implicated in controlling bioluminescence in other phyla. All critically examined triploblastic invertebrates release octopamine as a hormone, as a peripheral modulator and as a central neuromodulator in the nervous system, which exerts its action via evolutionary related G-protein-coupled receptors that activate cAMP. The evolution of the octopaminergic system seems fundamental for the evolution of efficient locomotory mechanisms, complex social interactions, and cognitive abilities of arthropods.     

Invertebrate trypsins: a review

Food protein hydrolysis, a crucial step in digestion, is catalyzed by trypsin enzymes from the digestive apparatus of invertebrates. Trypsin appeared early in evolution and occurs in all phyla and, in the digestive systems of invertebrates, it became the most abundant proteinase. As in vertebrates, invertebrate trypsin is also present in several forms (isoenzymes). Its physiological importance in food protein digestion in several invertebrate species has emerged with compelling evidence; and several other physiological functions, such as regulation of digestive functions, are now settled. Recent advances in the knowledge of invertebrate trypsin synthesis, regulation, genetics, catalytic characteristics; structure, evolution, as well as inhibition, especially in non-Drosophilidae insects and in some crustaceans are reviewed. Most of the existing information is largely based on the use of several tools, including molecular techniques, to answer many still open questions and solve medical, agricultural, and food quality problems.     

Non-target effects of the insecticide methoprene on molting in the estuarine crustacean Neomysis integer (Crustacea: Mysidacea)

Ecdysteroids, the molting hormones in crustaceans and other arthropods, play a crucial role in the control of growth, reproduction and embryogenesis of these organisms. Insecticides are often designed to target specific endocrine-regulated functions such as molting and larval development such as methoprene, a juvenile hormone analogue.The aim of this study was to examine the effects of methoprene on molting in a non-target species, the estuarine mysid Neomysis integer (Crustacea: Mysidacea). Mysids have been proposed as standard test organisms for evaluating the endocrine disruptive effect of chemicals. Juveniles (< 24 h) were exposed for 3 weeks to the nominal concentrations 0.01, 1 and 100 μg methoprene/l. Daily, present molts were checked and stored in 4% formaldehyde for subsequent growth measurements. Methoprene significantly delayed molting at 100 μg/l by decreasing the growth rate and increasing the intermolt period. This resulted in a decreased wet weight of the organism. The anti-ecdysteroidal properties of methoprene on mysid molting were also evaluated by determining the ability of exogenously administered 20-hydroxyecdysone, the active ecdysteroid in crustaceans, to protect against the observed methoprene effects. Co-exposure to 20-hydroxyecdysone did not mitigate methoprene effects on mysid molting. This study demonstrates the need for incorporating invertebrate-specific hormone-regulated endpoints in regulatory screening and testing programs for the detection of endocrine disruption caused by man-made chemicals.     

Nitric oxide synthase in invertebrates

Summary The gas nitric oxide is now recognized as an important signalling molecule that is synthesized froml-arginine by the enzyme nitric oxide synthase. This enzyme can be localized by different methods, including immunocytochemistry and the histochemical reaction for NADPH diaphorase. It has been demonstrated in various vertebrate cells and tissues, and recently several studies dealing with the production of nitric oxide in invertebrates have been published. Diploblastic animals, flatworms and nematodes seem to lack NADPH diaphorase activity but it has been found in the rest of the phyla studied. The most frequently reported sites for the production of nitric oxide are the central and peripheral nervous systems and, in primitive molluscs, the muscle cells. In insects, it has also been described in the Malpighian tubules. The roles of nitric oxide in invertebrates are closely related to the physiological actions described in vertebrates, namely, neurotransmission, defence, and salt and water balance. The recent cloning of the first nitric oxide synthase from an invertebrate source could open interesting avenues for further studies.     

Invertebrate models for biomedical research, testing, and education

Invertebrate animals have been used as medicinals for 4,000 years and have served as models for research and teaching since the late 1800s. Interest in invertebrate models has increased over the past several decades as the research community has responded to public concerns about the use of vertebrate animals in research. As a result, invertebrates are being evaluated and recognized as models for many diseases and conditions. Their use has led to discoveries in almost every area of biology and medicine--from embryonic development to aging processes. Species range from terrestrial invertebrates such as nematodes and insects to freshwater and marine life including planarians, crustaceans, molluscs, and many others. The most often used models are the fruit fly Drosophila melanogaster and the minuscule nematode Caenorhabditis elegans. Topics in this article are categorized by biologic system, process, or disease with discussion of associated invertebrate models. Sections on bioactive products discovered from invertebrates follow the models section, and the article concludes with uses of invertebrates in teaching. The models reviewed can serve as references for scientists, researchers, veterinarians, institutional animal care and use committees (IACUCs), and others interested in alternatives to vertebrate animals.     

Marine invertebrate genome sequences and our evolving understanding of animal immunity

Animal immunity is under intense evolutionary pressure, and the mechanisms that carry out recognition and elimination of pathogens are among the most rapidly evolving genetic systems. It is increasingly apparent that this has led to the emergence of novel molecular mechanisms not only among vertebrates, where immunity is by far best characterized, but also across invertebrate phyla. This propensity for rapid divergence has been a serious obstacle for progress in the field of comparative immunology. The variety of recent genome sequences from marine invertebrates representing new phyla offers a means to move forward in this area. Genome sequences provide much improved sensitivity for the detection of gene homologs and a framework for unbiased computational and experimental searches for novel immune mediators. Furthermore, new genomes now offer a more complete and unbiased view of immunity across bilaterian phyla, especially among deuterostomes. In this review we summarize these findings with particular attention toward immunity in Strongylocentrotus purpuratus, the purple sea urchin, and outline the changing perspective on the evolution of deuterostome immunity.     

The Freshwater Animal Diversity Assessment: an overview of the results

We present a summary of the results included in the different treatments in this volume. The diversity and distribution of vertebrates, insects, crustaceans, molluscs and a suite of minor phyla is compared and commented upon. Whereas the available data on vertebrates and some emblematic invertebrate groups such as Odonata (dragonflies and damselflies) allow for a credible assessment, data are deficient for many other groups. This is owing to knowledge gaps, both in geographical coverage of available data and/or lack of taxonomic information. These gaps need to be addressed urgently, either by liberating date from inaccessible repositories or by fostering taxonomic research. A similar effort is required to compile environmental and ecological information in order to enable cross-linking and analysis of these complementary data sets. Only in this way will it be possible to analyse information on freshwater biodiversity for sustainable management and conservation of the world’s freshwater resources. Guest editors: E. V. Balian, C. Lévêque, H. Segers & K. Martens Freshwater Animal Diversity Assessment     

The pH of body fluids from marine intertidal invertebrates

The pH of the body fluids of 25 species of marine invertebrates from nine phyla was determined at temperatures to which these animals were acclimated. The gastrovascular fluid of several coelenterates and one species of flatworm was found to have pH values approximating to that of sea water. The coelomic fluid of nemertine, sipinculid, echiuroid, and annelid worms, as well as the heart fluid of several molluscs and the sternal sinus fluid of decapod crustaceans, were characterized by more alkaline pH values. Echinoderm polian vesicle fluid was characterized by slightly acidic pH values. The importance of the pH of the body to the respiratory physiology of marine invertebrates is discussed.     

Juvenile hormone as a physiological regulator mediating phenotypic plasticity in pancrustaceans

Phenotypic plasticity and polyphenism, in which phenotypes can be changed depending on environmental conditions, are common in insects. Several studies focusing on physiological, developmental, and molecular processes underlying the plastic responses have revealed that similar endocrine mechanisms using juvenile hormone (JH) are used to coordinate the flexible developmental processes. This review discusses accumulated knowledge on the caste polyphenism in social insects (especially termites), the wing and the reproductive polyphenisms in aphids, and the nutritional polyphenism and sexual dimorphism in stag beetles. For the comparison with non-insect arthropods, extensive studies on the inducible defense (and reproductive polyphenism) in daphnids (crustacean) are also addressed. In all the cases, JH (and methyl farnesoate in daphnids) plays a central role in mediating environmental stimuli with morphogenetic processes. Since the synthetic pathways for juvenoids, i.e., the mevalonate pathway and downstream pathways to sesquiterpenoids, are conserved across pancrustacean lineages (crustaceans and hexapods including insects), the evolution of developmental regulation by juvenoids that control molting (ecdysis) and metamorphosis is suggested to have occurred in the ancestral arthropods. The discontinuous postembryonic development (i.e., molting) and the regulatory physiological factors (juvenoids) would have enabled plastic developmental systems observed in many arthropod lineages.     

Insulin and other islet hormones (somatostatin, glucagon and PP) in the neuroendocrine system of some lower vertebrates and that of invertebrates--a minireview

Onto- and phylogenetical studies of the evolution of cells, producing regulatory peptides, belonging to the "hormone families" of insulin, somatostatin, glucagon, and PP (the pancreatic polypeptide), have shown that the islets of Langerhans in vertebrates form a substantial part of the large neuroendocrine system (NES). The NES consists of three major parts, viz. (i) neuronal cells of the central and peripheral nervous systems, (ii) disseminated cells in the mucosa of the alimentary tract (and that of other hollow organs), (iii) the parenchymal cells of the classical endocrine glands. In the NES of coelenterates no evidence of islet hormone production has been obtained, so far. In invertebrates, belonging to the protostomian evolution line, the neuronal parts of the NES predominate markedly, and in the most highly developed phyla, such as artropods and molluscs, clear-cut evidence has been obtained for the presence of cells producing members of the islet hormone families. A "brain-gut axis" for all the four islet hormones is well established in the NES of the pro-craniates, i.e. in the invertebrates of the deuterostomian evolution line. Here, the gut endocrine cells are cells of the disseminated type in the epithelium of the mucosa. A separate islet organ does not occur in the NES until the appearance of the first vertebrates, viz. the Agnatha, some 500 million years ago. Here, a grossly visible islet organ exists, free from exocrine, acinar, pancreatic parenchyma. It is a two-hormone organ with insulin and somatostatin cells only.(ABSTRACT TRUNCATED AT 250 WORDS)