Growth factors, heat-shock proteins and regeneration in echinoderms

Comparative physiological study of sea cucumbers from eastern waters of United States

Sea cucumbers, belonging to the phylum Echinodermata, are known to possess valuable bioactive compounds that have medicinal properties. In several countries, such as Korea, China, and Japan, they are cultured in the aquaculture industries for food and medicinal purposes. Research has shown that different species of sea cucumbers each possesses unique medicinal values. As a result, we strive towards finding species with better health resilience in aquaculture system to be cultured for nutritional and medicinal purposes. In this paper, we compared the physiological and immunological parameters of three species of sea cucumbers, Cucumaria frondosa (C. frondosa), Isostychopus badionotus (I. badionotus), and Pentacta pygmaea (P. Pygmaea) from the waters of the eastern United States as they have not been studied extensively. Four different cells of sea cucumbers, phagocytic, red spherule, white spherule, and vibratile cells, that contribute to their immunity were counted. C. frondosa exhibited the highest concentrations of phagocytic cells, white spherule cells, and vibratile cells, compared to the two other species. Due to its high phagocytic cell concentration, the highest phagocytic capacity was seen in C. frondosa although it was not statistically significant. We also observed that C. frondosa had the highest total cell count and the highest concentration of coelomic protein among the three species. Lastly, C. frondosa possessed the highest lysozyme activity. Taken together, we concluded that C. frondosa is the best of the three species compared to be reared in the aquaculture systems for use in the food and biomedicine industries due to its immunological and physiological properties.

The salamander blastema within the broader context of metazoan regeneration

Throughout the animal kingdom regenerative ability varies greatly from species to species, and even tissue to tissue within the same organism. The sheer diversity of structures and mechanisms renders a thorough comparison of molecular processes truly daunting. Are "blastemas" found in organisms as distantly related as planarians and axolotls derived from the same ancestral process, or did they arise convergently and independently? Is a mouse digit tip blastema orthologous to a salamander limb blastema? In other fields, the thorough characterization of a reference model has greatly facilitated these comparisons. For example, the amphibian Spemann-Mangold organizer has served as an amazingly useful comparative template within the field of developmental biology, allowing researchers to draw analogies between distantly related species, and developmental processes which are superficially quite different. The salamander limb blastema may serve as the best starting point for a comparative analysis of regeneration, as it has been characterized by over 200 years of research and is supported by a growing arsenal of molecular tools. The anatomical and evolutionary closeness of the salamander and human limb also add value from a translational and therapeutic standpoint. Tracing the evolutionary origins of the salamander blastema, and its relatedness to other regenerative processes throughout the animal kingdom, will both enhance our basic biological understanding of regeneration and inform our selection of regenerative model systems.

Differentially expressed chaperone genes reveal a stress response required for unidirectional regeneration in the basal chordate Ciona

BACKGROUND

Unidirectional regeneration in the basal chordate Ciona intestinalis involves the proliferation of adult stem cells residing in the branchial sac vasculature and the migration of progenitor cells to the site of distal injury. However, after the Ciona body is bisected, regeneration occurs in the proximal but not in the distal fragments, even if the latter include a part of the branchial sac with stem cells. A transcriptome was sequenced and assembled from the isolated branchial sacs of regenerating animals, and the information was used to provide insights into the absence of regeneration in distal body fragments.

RESULTS

We identified 1149 differentially expressed genes, which were separated into two major modules by weighted gene correlation network analysis, one consisting of mostly upregulated genes correlated with regeneration and the other consisting of only downregulated genes associated with metabolism and homeostatic processes. The hsp70, dnaJb4, and bag3 genes were among the highest upregulated genes and were predicted to interact in an HSP70 chaperone system. The upregulation of HSP70 chaperone genes was verified and their expression confirmed in BS vasculature cells previously identified as stem and progenitor cells. siRNA-mediated gene knockdown showed that hsp70 and dnaJb4, but not bag3, are required for progenitor cell targeting and distal regeneration. However, neither hsp70 nor dnaJb4 were strongly expressed in the branchial sac vasculature of distal fragments, implying the absence of a stress response. Heat shock treatment of distal body fragments activated hsp70 and dnaJb4 expression indicative of a stress response, induced cell proliferation in branchial sac vasculature cells, and promoted distal regeneration.

CONCLUSIONS

The chaperone system genes hsp70, dnaJb4, and bag3 are significantly upregulated in the branchial sac vasculature following distal injury, defining a stress response that is essential for regeneration. The stress response is absent from distal fragments, but can be induced by a heat shock, which activates cell division in the branchial sac vasculature and promotes distal regeneration. This study demonstrates the importance of a stress response for stem cell activation and regeneration in a basal chordate, which may have implications for understanding the limited regenerative activities in other animals, including vertebrates.

The Stress Response of the Holothurian Central Nervous System: A Transcriptomic Analysis

Injury to the central nervous system (CNS) results in permanent damage and lack of function in most vertebrate animals, due to their limited regenerative capacities. In contrast, echinoderms can fully regenerate their radial nerve cord (RNC) following transection, with little to no scarring. Investigators have associated the regenerative capacity of some organisms to the stress response and inflammation produced by the injury. Here, we explore the gene activation profile of the stressed holothurian CNS. To do this, we performed RNA sequencing on isolated RNC explants submitted to the stress of transection and enzyme dissection and compared them with explants kept in culture for 3 days following dissection. We describe stress-associated genes, including members of heat-shock families, ubiquitin-related pathways, transposons, and apoptosis that were differentially expressed. Surprisingly, the stress response does not induce apoptosis in this system. Other genes associated with stress in other animal models, such as hero proteins and those associated with the integrated stress response, were not found to be differentially expressed either. Our results provide a new viewpoint on the stress response in the nervous system of an organism with amazing regenerative capacities. This is the first step in deciphering the molecular processes that allow echinoderms to undergo fully functional CNS regeneration, and also provides a comparative view of the stress response in other organisms.

Potential of Epidermal Growth Factor-like Peptide from the Sea Cucumber Stichopus horrens to Increase the Growth of Human Cells: In Silico Molecular Docking Approach

The sea cucumber is prominent as a traditional remedy among Asians for wound healing due to its high capacity for regeneration after expulsion of its internal organs. A short peptide consisting of 45 amino acids from transcriptome data of Stichopus horrens (Sh-EGFl-1) shows a convincing capability to promote the growth of human melanoma cells. Molecular docking of Sh-EGFl-1 peptide with human epidermal growth factor receptor (hEGFR) exhibited a favorable intermolecular interaction, where most of the Sh-EGFl-1 residues interacted with calcium binding-like domains. A superimposed image of the docked structure against a human EGF–EGFR crystal model also gave an acceptable root mean square deviation (RMSD) value of less than 1.5 Å. Human cell growth was significantly improved by Sh-EGFl-1 peptide at a lower concentration in a cell proliferation assay. Gene expression profiling of the cells indicated that Sh-EGFl-1 has activates hEGFR through five epidermal growth factor signaling pathways; phosphoinositide 3-kinase (PI3K), mitogen-activated protein kinase (MAPK), phospholipase C gamma (PLC-gamma), Janus kinase-signal transducer and activator of transcription (JAK-STAT) and Ras homologous (Rho) pathways. All these pathways triggered cells’ proliferation, differentiation, survival and re-organization of the actin cytoskeleton. Overall, this marine-derived, bioactive peptide has the capability to promote proliferation and could be further explored as a cell-growth-promoting agent for biomedical and bioprocessing applications.

Stress and immune response to bacterial LPS in the sea urchin Paracentrotus lividus (Lamarck, 1816)

The immune system of the sea urchin species Paracentrotus lividus is highly complex and, as yet, poorly understood. P. lividus coelomocytes mediate immune response through phagocytosis and encapsulation of non-self particles, in addition to the production of antimicrobial molecules. Despite this understanding, details of exactly how these processes occur and the mechanisms which drive them are still in need of clarification. In this study, we show how the bacterial lipopolysaccharides (LPS) is able to induce a stress response which increases the levels of the heat shock proteins HSP70 and HSP90 only a few hours after treatment. This study also shows that LPS treatment increases the expression of the β-thymosin-derivated protein paracentrin, the precursor of antimicrobial peptides.

Neurogenesis in the sea urchin embryo is initiated uniquely in three domains

Many marine larvae begin feeding within a day of fertilization, thus requiring rapid development of a nervous system to coordinate feeding activities. Here, we examine the patterning and specification of early neurogenesis in sea urchin embryos. Lineage analysis indicates that neurons arise locally in three regions of the embryo. Perturbation analyses showed that when patterning is disrupted, neurogenesis in the three regions is differentially affected, indicating distinct patterning requirements for each neural domain. Six transcription factors that function during proneural specification were identified and studied in detail. Perturbations of these proneural transcription factors showed that specification occurs differently in each neural domain prior to the Delta-Notch restriction signal. Though gene regulatory network state changes beyond the proneural restriction are largely unresolved, the data here show that the three neural regions already differ from each other significantly early in specification. Future studies that define the larval nervous system in the sea urchin must therefore separately characterize the three populations of neurons that enable the larva to feed, to navigate, and to move food particles through the gut.

Whole genome detection of signature of positive selection in African cattle reveals selection for thermotolerance

As African indigenous cattle evolved in a hot tropical climate, they have developed an inherent thermotolerance; survival mechanisms include a light-colored and shiny coat, increased sweating, and cellular and molecular mechanisms to cope with high environmental temperature. Here, we report the positive selection signature of genes in African cattle breeds which contribute for their heat tolerance mechanisms. We compared the genomes of five indigenous African cattle breeds with the genomes of four commercial cattle breeds using cross-population composite likelihood ratio (XP-CLR) and cross-population extended haplotype homozygosity (XP-EHH) statistical methods. We identified 296 (XP-EHH) and 327 (XP-CLR) positively selected genes. Gene ontology analysis resulted in 41 biological process terms and six Kyoto Encyclopedia of Genes and Genomes pathways. Several genes and pathways were found to be involved in oxidative stress response, osmotic stress response, heat shock response, hair and skin properties, sweat gland development and sweating, feed intake and metabolism, and reproduction functions. The genes and pathways identified directly or indirectly contribute to the superior heat tolerance mechanisms in African cattle populations. The result will improve our understanding of the biological mechanisms of heat tolerance in African cattle breeds and opens an avenue for further study.

Cellular responses and HSP70 expression during wound healing in Holothuria tubulosa (Gmelin, 1788)

Wound repair is a key event in the regeneration mechanisms of echinoderms. We studied, at the behavioural, cellular and molecular levels, the wound healing processes in Holothuria tubulosa after injuries to the body wall. The experiments were performed for periods of up to 72 h, and various coelomocyte counts, as well as the expression of heat shock proteins (HS27, HSP70 and HSP90), were recorded. Dermal wound healing was nearly complete within 72 h. In the early stages, we observed the injured animals twisting their bodies to keep their injuries on the surface of the water for the extrusion of the buccal pedicles. At the cellular level, we found time-dependent variations in the circulating coelomocyte counts. After injury, in particular, we observed a significant increase in spherule cells at 2.5 h post-injury. Using the western blot method, we observed and reported that the wounds produced, compared with controls, a significant increase in HSP27 and HSP70 expression in coelomocytes, whereas HSP70 was increased in scar tissue and HSP90 was increased only in cell-free coelomic fluid. These results highlight that the wounds were responsible for the stress condition with the induction of cellular and biochemical responses.

Immune suppression of the echinoderm Asterias rubens (L.) following long-term ocean acidification

We compared effects of exposure to predict near-future (2100) ocean acidification (OA; pH 7.7) and normal seawater (Control; pH 8.1) on immune and stress responses in the adult sea star Asterias rubens. Analyses were made after one week and after six months of continuous exposure. Following one week exposure to acidified water, the pH of coelomic fluid was significantly reduced. Levels of the chaperon Hsp70 were elevated while key cellular players in immunity, coelomocytes, were reduced by approximately 50%. Following long-term exposure (six months) levels of Hsp70 returned to control values, whereas immunity was further impaired, evidenced by the reduced phagocytic capacity of coelomocytes and inhibited activation of p38 MAP-kinase. Such impacts of reduced seawater pH may have serious consequences for resistance to pathogens in a future acidified ocean.

Gene expression of axon growth promoting factors in the deer antler

The annual regeneration cycle of deer (Cervidae, Artiodactyla) antlers represents a unique model of epimorphic regeneration and rapid growth in adult mammals. Regenerating antlers are innervated by trigeminal sensory axons growing through the velvet, the modified form of skin that envelopes the antler, at elongation velocities that reach one centimetre per day in the common deer (Cervus elaphus). Several axon growth promoters like NT-3, NGF or IGF-1 have been described in the antler. To increase the knowledge on the axon growth environment, we have combined different gene-expression techniques to identify and characterize the expression of promoting molecules not previously described in the antler velvet. Cross-species microarray analyses of deer samples on human arrays allowed us to build up a list of 90 extracellular or membrane molecules involved in axon growth that were potentially being expressed in the antler. Fifteen of these genes were analysed using PCR and sequencing techniques to confirm their expression in the velvet and to compare it with the expression in other antler and skin samples. Expression of 8 axon growth promoters was confirmed in the velvet, 5 of them not previously described in the antler. In conclusion, our work shows that antler velvet provides growing axons with a variety of promoters of axon growth, sharing many of them with deer's normal and pedicle skin.

Molecular and cellular aspects of amphibian lens regeneration

Lens regeneration among vertebrates is basically restricted to some amphibians. The most notable cases are the ones that occur in premetamorphic frogs and in adult newts. Frogs and newts regenerate their lens in very different ways. In frogs the lens is regenerated by transdifferentiation of the cornea and is limited only to a time before metamorphosis. On the other hand, regeneration in newts is mediated by transdifferentiation of the pigment epithelial cells of the dorsal iris and is possible in adult animals as well. Thus, the study of both systems could provide important information about the process. Molecular tools have been developed in frogs and recently also in newts. Thus, the process has been studied at the molecular and cellular levels. A synthesis describing both systems was long due. In this review we describe the process in both Xenopus and the newt. The known molecular mechanisms are described and compared.

Regeneration in crinoids

Regeneration is a biological phenomenon that occurs in a wide range of animals, and is considered to involve different types of cells including those that are considered to be stem cells. Among the echinoderms, which is a phylum with many regenerating members, crinoids (feather stars and sea lilies) are known to possess high potential of regeneration and are able to regenerate most of their organs. In particular, arm regeneration has been studied using the feather star. During regeneration, coelomocytes and amoebocytes originating from the coelomic canal and the brachial nerve, respectively, migrate to the distal wound area and are involved in the regenerative process. A blastema is formed at the regenerating tip and is derived from migratory amoebocytes. On the other hand, migratory coelomocytes contribute to regenerate the coelomic system. Cells proliferate at the blastema, coelomic canals and brachial nerve. Since the migrating cells differentiate into new structures of the arm, they are considered presumably undifferentiated multipotent stem cells. To deepen our understanding of stem cells in general, we may benefit from an approach from a comparative point of view. Further molecular analyses would increase our knowledge of stem cells in crinoids and allow comparative studies to be possible.

Gene expression profiles of lens regeneration and development in Xenopus laevis

Seven hundred and thirty-four unique genes were recovered from a cDNA library enriched for genes up-regulated during the process of lens regeneration in the frog Xenopus laevis. The sequences represent transcription factors, proteins involved in RNA synthesis/processing, components of prominent cell signaling pathways, genes involved in protein processing, transport, and degradation (e.g., the ubiquitin/proteasome pathway), matrix metalloproteases (MMPs), as well as many other proteins. The findings implicate specific signal transduction pathways in the process of lens regeneration, including the FGF, TGF-beta, MAPK, Retinoic acid, Wnt, and hedgehog signaling pathways, which are known to play important roles in eye/lens development and regeneration in various systems. In situ hybridization revealed that the majority of genes recovered are expressed during embryogenesis, including in eye tissues. Several novel genes specifically expressed in lenses were identified. The suite of genes was compared to those up-regulated in other regenerating tissues/organisms, and a small degree of overlap was detected.

NGFFFamide and echinotocin: structurally unrelated myoactive neuropeptides derived from neurophysin-containing precursors in sea urchins

The myoactive neuropeptide NGIWYamide was originally isolated from the holothurian (sea cucumber) Apostichopus japonicus but there is evidence that NGIWYamide-like peptides also occur in other echinoderms. Here we report the discovery of a gene in the sea urchin Strongylocentrotus purpuratus that encodes two copies of an NGIWYamide-like peptide: Asn-Gly-Phe-Phe-Phe-(NH(2)) or NGFFFamide. Interestingly, the C-terminal region of the NGFFFamide precursor shares sequence similarity with neurophysins, carrier proteins hitherto uniquely associated with precursors of vasopressin/oxytocin-like neuropeptides. Thus, the NGFFFamide precursor is the first neurophysin-containing neuropeptide precursor to be discovered that does not contain a vasopressin/oxytocin-like peptide. However, it remains to be determined whether neurophysin acts as a carrier protein for NGFFFamide. The S. purpuratus genome also contains a gene encoding a precursor comprising a neurophysin polypeptide and 'echinotocin' (CFISNCPKGamide) - the first vasopressin/oxytocin-like peptide to be identified in an echinoderm. Therefore, in S. purpuratus there are two genes encoding precursors that have a neurophysin domain but which encode neuropeptides that are structurally unrelated. Furthermore, both NGFFFamide and echinotocin cause contraction of tube foot and oesophagus preparations from the sea urchin Echinus esculentus, consistent with the myoactivity of NGIWYamide in sea cucumbers and the myoactivity of vasopressin/oxytocin-like peptides in other animal phyla. Presumably the NGFFFamide precursor acquired its neurophysin domain following partial or complete duplication of a gene encoding a vasopressin/oxytocin-like peptide, but it remains to be determined when in evolutionary history this occurred.

Identification of genes associated with regenerative success of Xenopus laevis hindlimbs

BACKGROUND

Epimorphic regeneration is the process by which complete regeneration of a complex structure such as a limb occurs through production of a proliferating blastema. This type of regeneration is rare among vertebrates but does occur in the African clawed frog Xenopus laevis, traditionally a model organism for the study of early development. Xenopus tadpoles can regenerate their tails, limb buds and the lens of the eye, although the ability of the latter two organs to regenerate diminishes with advancing developmental stage. Using a heat shock inducible transgene that remains silent unless activated, we have established a stable line of transgenic Xenopus (strain N1) in which the BMP inhibitor Noggin can be over-expressed at any time during development. Activation of this transgene blocks regeneration of the tail and limb of Xenopus tadpoles.

RESULTS

In the current study, we have taken advantage of the N1 transgenic line to directly compare morphology and gene expression in same stage regenerating vs. BMP signalling deficient non-regenerating hindlimb buds. The wound epithelium of N1 transgenic hindlimb buds, which forms over the cut surface of the limb bud after amputation, does not transition normally into the distal thickened apical epithelial cap. Instead, a basement membrane and dermis form, indicative of mature skin. Furthermore, the underlying mesenchyme remains rounded and does not expand to form a cone shaped blastema, a normal feature of successful regeneration. Using Affymetrix Gene Chip analysis, we have identified genes linked to regenerative success downstream of BMP signalling, including the BMP inhibitor Gremlin and the stress protein Hsp60 (no blastema in zebrafish). Gene Ontology analysis showed that genes involved in embryonic development and growth are significantly over-represented in regenerating early hindlimb buds and that successful regeneration in the Xenopus hindlimb correlates with the induction of stress response pathways.

CONCLUSION

N1 transgenic hindlimbs, which do not regenerate, do not form an apical epithelial cap or cone shaped blastema following amputation. Comparison of gene expression in stage matched N1 vs. wild type hindlimb buds has revealed several new targets for regeneration research.

Expression of heat-shock protein 70 during limb development and regeneration in the axolotl

Urodele amphibians (e.g., axolotls) have the unique ability, among vertebrates, to regenerate perfectly many parts of their body after amputation. The limb has been the most widely studied regenerating structure in these organisms and provides an ideal model in which to understand how vertebrates can regenerate complex tissues. The present study focuses on Hsp-70, a member of the stress-related heat-shock protein family. This protein is normally induced after a stress or trauma such as heat-shock, ultraviolet irradiation, or wounding. Thus, studying its expression during axolotl limb regeneration, a response to an important traumatic event (amputation), is of great interest to further understand how the regenerative process is mediated. Using molecular biology and biochemical techniques, we have characterized both the spatiotemporal and quantitative expression patterns of Hsp-70 in axolotl development and regeneration. Our results show that Hsp-70 is expressed and regulated during axolotl development as in other vertebrates. Our data also demonstrate an up-regulation of the RNA transcript for Hsp-70 during limb regeneration as early as 24 hr after amputation that is maintained up to early differentiation. We also demonstrate a similar pattern of expression for the protein during regeneration. Finally, we show that axolotl Hsp-70 is induced threefold after heat-shock as observed in other vertebrates.

Alteration and recovery of appetitive behaviour following nerve section in the starfish Asterias rubens

The starfish Asterias rubens is an invertebrate deuterostome whose nervous system shows remarkable regenerative properties. To understand when full functionality of a damaged part of the nervous system recovers, and to follow nerve regeneration in detail, we carried out behavioural experiments with 29 starfishes that had the nerve in one of the arms sectioned in a mid-arm position. Loss and recovery of normal behaviour was followed by video analysis of animal performance in an appetitive behavioural test. When compared to 13 control (unoperated) animals, the appetitive response of freshly sectioned animals is normal initially, progressively deteriorates up to 40 days after the lesion, and then gradually improves until 60 days, when recovery is complete. This is true only when one of the leading arms in the appetitive test is a sectioned arm; turning the starfish so that both the leading arms facing the prey are unlesioned, results in normal behaviour even at 40 days after the cut. Thus, regeneration is a multi-step process whose time course coincides with anatomical regeneration. At intermediate times the animals have coordination problems in an appetitive behaviour test and these give some insights into how arms may inter-communicate to organize concerted movements.

Microscopic overview of crinoid regeneration

Crinoids are well known for their striking regenerative potential and can rapidly and completely regenerate arms lost following self-induced or traumatic amputation. Thus they provide a valuable experimental model for investigation of the regenerative process from the macroscopic to the molecular level. In these last years we have studied in detail the overall process of arm regeneration in the comatulid Antedon mediterranea. This phenomenon can be described on the whole as a typical blastemal regeneration in which new structures develop from migratory pluripotential, actively proliferating cells in the presence of presumptive regulatory factors. The overall process can be subdivided into three main phases: a repair phase, an early regenerative phase, and an advanced regenerative phase, whose crucial aspects are related to common fundamental mechanisms such as cell migration and proliferation, intervention of stem cells and/or dedifferentiated cells, contribution of putative growth factors, particularly in terms of specific neurally derived factors, and mechanisms of pattern formation. This article focuses on the main aspects of the phenomenon and gives a brief account of the most recent and relevant results. Our approach employs classical methods of light (LM) and electron (TEM and SEM) microscopy, immunocytochemistry, and histofluorescence on experimentally induced arm regenerations of standard or abnormal type obtained in significantly different experimental conditions, including extreme mutilations (explants) or exposure to pseudo-estrogenic environmental contamination.

Regenerative response and endocrine disrupters in crinoid echinoderms: arm regeneration in Antedon mediterranea after experimental exposure to polychlorinated biphenyls

Regenerative phenomena, which have the advantage of reproducing developmental processes in the adult organism, are very sensitive to environmental stress and represent stages that can be monitored for damage at the whole-organism, cellular and molecular levels. Some persistent and ubiquitous pollutants, which can affect the natural environment because of their bioaccumulation in organisms, exert their effects by acting as ‘endocrine disrupters’. In this respect, they can cause dysfunction in steroid hormone production/metabolism and activity by their dramatic effects on gene expression, reproductive competence and growth. The aim of our present research was to assess the impact of such compounds on adult echinoderm reproductive physiology with particular reference to regeneration potential. It is known that vertebrate-type steroids are synthesized by echinoderms and play a role in the control of growth and reproduction. Our experimental model is the crinoid Antedon mediterranea, selected on the basis of its previously explored regenerative capabilities at the level of the arms. The regeneration response, analyzed at the tissue and cellular levels using both light and electron microscopy and immunocytochemistry, was employed to monitor the effects of exposure to persistent endocrine disrupter micropollutants such as polychlorinated biphenyls (PCBs) by means of laboratory tests performed under controlled conditions in terms of environmental variables and contamination levels. Our results indicate that exposure to endocrine disrupter compounds such as PCBs can induce anomalies in regeneration times, morphology and developmental mechanisms that can be interpreted in the light of significant dysfunctions in the endocrine mechanisms controlling regenerative development.