[Show abstract][Hide abstract] ABSTRACT: The compass depressors (CDs) of the sea-urchin lantern are ligaments consisting mainly of discontinuous collagen fibrils associated with a small population of myocytes. They are mutable collagenous structures, which can change their mechanical properties rapidly and reversibly under nervous control. The aims of this investigation were to characterise the baseline (i.e. unmanipulated) static mechanical properties of the CDs of Paracentrotus lividus by means of creep tests and incremental force-extension tests, and to determine the effects on their mechanical behaviour of a range of agents. Under constant load the CDs exhibited a three-phase creep curve, the mean coefficient of viscosity being 561±365 MPa.s. The stress-strain curve showed toe, linear and yield regions; the mean strain at the toe-linear inflection was 0.86±0.61; the mean Young's modulus was 18.62±10.30 MPa; and the mean tensile strength was 8.14±5.73 MPa. Hyaluronidase from Streptomyces hyalurolyticus had no effect on creep behaviour, whilst chondroitinase ABC prolonged primary creep but had no effect on secondary creep or on any force-extension parameters; it thus appears that neither hyaluronic acid nor sulphated glycosaminoglycans have an interfibrillar load transfer function in the CD. Acetylcholine, the muscarinic agonists arecoline and methacholine, and the nicotinic agonists nicotine and 1-[1-(3,4-dimethyl-phenyl)-ethyl]-piperazine produced an abrupt increase in CD viscosity; the CDs were not differentially sensitive to muscarinic or nicotinic agonists. CDs showed either no, or no consistent, response to adrenaline, L-glutamic acid, 5-hydroxytryptamine and γ-aminobutyric acid. Synthetic echinoid tensilin-like protein had a weak and inconsistent stiffening effect, indicating that, in contrast to holothurian tensilins, the echinoid molecule may not be involved in the regulation of collagenous tissue tensility. We compare in detail the mechanical behaviour of the CD with that of mammalian tendon and highlight its potential as a model system for investigating poorly understood aspects of the ontogeny and phylogeny of vertebrate collagenous tissues.
[Show abstract][Hide abstract] ABSTRACT: Collagen has become a key-molecule in cell culture studies and in the tissue engineering field. Industrially, the principal sources of collagen are calf skin and bones which, however, could be associated to risks of serious disease transmission. In fact, collagen derived from alternative and riskless sources is required, and marine organisms are among the safest and recently exploited ones. Sea urchins possess a circular area of soft tissue surrounding the mouth, the peristomial membrane (PM), mainly composed by mammalian-like collagen. The PM of the edible sea urchin Paracentrotus lividus therefore represents a potential unexploited collagen source, easily obtainable as a food industry waste product. Our results demonstrate that it is possible to extract native collagen fibrils from the PM and produce suitable substrates for in vitro system. The obtained matrices appear as a homogeneous fibrillar network (mean fibril diameter 30-400 nm and < 2 μm) and display remarkable mechanical properties in term of stiffness (146 ± 48 MPa) and viscosity (60.98 ± 52.07 GPa·s). In vitro tests with horse pbMSC show a good biocompatibility in terms of overall cell growth. The obtained results indicate that the sea urchin P. lividus can be a valuable low-cost collagen source for mechanically resistant biomedical devices.
[Show abstract][Hide abstract] ABSTRACT: Echinoderms possess unique connective tissues (Mutable Collagenous Tissues, MCT) which can dynamically modulate their mechanical state, reversibly switching between stiff and compliant conditions. From a structural point of view MCTs are composed of the same main components as all mammalian connective tissues: cells, collagen and other extracellular matrix molecules, such as proteoglycans (PGs) and glycosaminoglycans (GAGs). These latter are known to play an important role in the mechanical state variations shown by the uterine cervix during pregnancy, the only example of a mammalian dynamic connective tissue.
In this work we review the main results obtained during a three year project that concern the presence, amount and possible role of PGs and GAGs in two established MCT models in echinoderms: the peristomial membrane (PM) and the compass depressor ligament (CDL) of the common sea urchin Paracentrotus lividus, Lamarck 1816. Changes occurring between the different mechanical states (compliant, standard, stiff) of the two MCT’s structures were investigated with different and integrated experiments. In particular we employed a highly multidisciplinary approach based on histological, biochemical and biomechanical evaluations, including light and electron microscopy, histochemistry, SDS-PAGE, quantification techniques, enzymatic treatment as well as specific mechanical testing.
We confirmed the presence and described the distribution of hyaluronic acid and other collagen-associated GAGs, the latter being distributed periodically along the collagen fibril in a pattern that does not vary between the different mechanical states. Different classes of GAGs are present in MCTs (weakly, highly and not sulfated) but, as for the total GAG content, each class is present in similar amounts in the different mechanical states. The two MCTs display different PG patterns, which possibly reflects the different functionality of the tissues. Mechanical tests coupled with enzymatic treatment (chondroitinase ABC, hyaluronidase) indicate that GAGs are mainly involved in the stabilization of collagen disposition with very little contribution to the overall mechanical properties.
In conclusion, the mechanical state of MCTs is not correlated with differences in GAG distribution, composition or quantity. The GAGs of MCTs are structural molecules that are not the main determinants of MCT tensile properties and appear to be involved only indirectly in mutability phenomena.
[Show abstract][Hide abstract] ABSTRACT: Although sponges are still often considered to be simple, inactive animals, both larvae and adults of different species show clear coordination phenomena triggered by extrinsic and intrinsic stimuli. Chondrosia reniformis, a common Mediterranean demosponge, lacks both endogenous siliceous spicules and reinforcing spongin fibers and has a very conspicuous collagenous mesohyl. Although this species can stiffen its body in response to mechanical stimulation when handled, almost no quantitative data are available in the literature on this phenomenon. The present work was intended to quantify the dynamic response to mechanical stimulation both of intact animals and isolated tissue samples in order to evaluate: (i) the magnitude of stiffening; (ii) the relationship between the amount of stimulation and the magnitude of the stiffening response; (iii) the ability of the whole body to react to localized stimulation; (iv) the possible occurrence of a conduction mechanism and the role of the exopinacoderm (outer epithelium). Data on mesohyl tensility obtained with mechanical tests confirmed the difference between stimulated and non-stimulated isolated tissue samples, showing a significant relationship between ectosome stiffness and the amount of mechanical stimulation. Our experiments revealed a significant difference in tensility between undisturbed and maximally stiffened sponges and evidence of signal transmission that requires a continuous exopinacoderm. We also provide further evidence for the presence of a chemical factor that alters the interaction between collagen fibrils, thereby changing the mechanical properties of the mesohyl.
[Show abstract][Hide abstract] ABSTRACT: Among echinoderms, crinoids are well known for their remarkable regenerative potential. Regeneration depends mainly on progenitor cells (undifferentiated or differentiated), which migrate and proliferate in the lesion site. The crucial role of the "progenitor" elements involved in the regenerative processes, in terms of cell recruitment, sources, and fate, is a central problem in view of its topical interest and biological implications. The spectacular regenerative potential of crinoids is used to replace lost internal and external organs. In particular, the process of arm regeneration in the feather star Antedon mediterranea is the regeneration model most extensively explored to date. We have addressed the morphological and functional characterization of the cell phenotypes responsible for the arm regenerative processes by using an in vitro approach. This represents the first successful attempt to culture cells involved in crinoid regeneration. A comparison of these results with others from previous in vivo investigations confirms the diverse cell types contributing to regeneration and underscores their involvement in migration, proliferation, and dedifferentiation processes.
No preview · Article · Jun 2014 · Cell and Tissue Research
[Show abstract][Hide abstract] ABSTRACT: Echinoderms and sponges share a unique feature that helps them face predators and other environmental pressures. They both possess collagenous tissues with adaptable viscoelastic properties. In terms of morphology these structures are typical connective tissues containing collagen fibrils, fibroblast- and fibroclast-like cells, as well as unusual components such as, in echinoderms, neurosecretory-like cells that receive motor innervation. The mechanisms underpinning the adaptability of these tissues are not completely understood. Biomechanical changes can lead to an abrupt increase in stiffness (increasing protection against predation) or to the detachment of body parts (in response to a predator or to adverse environmental conditions) that are regenerated. Apart from these advantages, the responsiveness of echinoderm and sponge collagenous tissues to ionic composition and temperature makes them potentially vulnerable to global environmental changes.
Full-text · Article · Feb 2014 · Marine environmental research
[Show abstract][Hide abstract] ABSTRACT: Although sponges are still often considered to be simple, inactive animals, both larvae and adults of different species show clear coordination phenomena triggered by both extrinsic and intrinsic stimuli. Chondrosia reniformis (Nardo, 1847), a common Mediterranean demosponge, lacks both endogenous siliceous spicules and reinforcing spongin fibers and has a very conspicuous collagenous mesohyl. Although this species can stiffen its whole body in response to localized mechanical stimulation, no data are available in the literature on the propagation of this stiffening response. The present work was intended to demonstrate: 1) the ability of the whole body to react to localized stimulation; 2) the possible occurrence of a conduction mechanism; 3) the role of the exopinacoderm in the propagation of the stiffening responses. Data on mesohyl tensility obtained with mechanical tests confirmed the ability of the sponge to react to local stimulation by stiffening regions 2 cm away from the stimulated area, suggesting the presence of a conduction mechanism that propagates from the stimulated spot. Creating a discontinuity in the exopinacoderm, by removing 1 mm of the sponge surface in the area surrounding the stimulation spot, resulted in a strong decrease in the capability of the sponge to stiffen at 2 cm distance, which suggests that the exopinacoderm could play a role in the propagation of the stiffening response. We also provide further evidence (following Wilkie et al., 2006) for the presence of a chemical factor that alters the interaction between collagen fibrils, thereby stiffening the sponge mesohyl.
[Show abstract][Hide abstract] ABSTRACT: In the present work, primary cell cultures from ovaries of the edible sea urchin Paracentrotus lividus were developed in order to provide a simple and versatile experimental tool for researches in echinoderm reproductive biology. Ovary cell phenotypes were identified and characterized by different microscopic techniques. Although cell cultures could be produced from ovaries at all stages of maturation, the cells appeared healthier and viable, displaying a higher survival rate, when ovaries at early stages of gametogenesis were used. In terms of culture medium, ovarian cells were successfully cultured in modified Leibovitz-15 medium, whereas poor results were obtained in minimum essential medium Eagle and medium 199. Different substrates were tested, but ovarian cells completely adhered only on poly-L-lysine. To improve in vitro conditions and stimulate cell proliferation, different serum-supplements were tested. Fetal calf serum and an originally developed pluteus extract were detrimental to cell survival, apparently accelerating processes of cell death. In contrast, cells cultured with sea urchin egg extract appeared larger and healthier, displaying an increased longevity that allowed maintaining them for up to 1 month. Overall, our study provides new experimental bases and procedures for producing successfully long-term primary cell cultures from sea urchin ovaries offering a good potential to study echinoid oogenesis in a controlled system and to investigate different aspects of echinoderm endocrinology and reproductive biology.
No preview · Article · Sep 2013 · In Vitro Cellular & Developmental Biology - Animal
[Show abstract][Hide abstract] ABSTRACT: Mutable collagenous tissues (MCTs) of echinoderms can be regarded as intelligent and dynamic biomaterials, due to their ability to reversibly change their mechanical properties in a short physiological time span. This mutability phenomenon is nervously mediated and involves secreted factors of the specialized 'juxtaligamental' cells, which, when released into the extracellular matrix (ECM), change the cohesive forces between collagen fibrils. MCTs exist in nature in several forms, including some associated with echinoderm autotomy mechanisms. Since the molecular mechanism of mutability is still incompletely understood, the aim of this work was to provide a detailed biochemical analysis of a typical mutable collagenous structure and to identify possible correlations between its biochemistry and mechanical states. A better understanding of the mutability phenomena is likely to provide a unique opportunity to develop new concepts that can be applied in the design of dynamic biomaterial for tissue regeneration, leading to new strategies in regenerative medicine. The MCT model used was the compass depressor ligament (CDL) of a sea urchin (Paracentrotus lividus), which was analyzed in different mechanical states, mimicking the mutability phenomenon. Spectroscopic techniques, namely Fourier transform infrared (FT-IR) and confocal Raman microscopy, were used to identify the specific molecular components that contribute to the CDL biochemical microenvironment and to investigate the possibility that remodelling/synthesis of new ECM components occurs during the mutability phenomenon by analogy with events during pregnancy in the uterine cervix of mammals (which also consists mainly of mechanically adaptable connective tissues). The results demonstrate that CDL ECM includes collagen with biochemical similarities to mammalian type I collagen, as well as sulphated glycosaminoglycans (GAGs). CDL mutability seems to involve a molecular rearrangement of the ECM, without synthesis of new ECM components. Although there were no significant biochemical differences between CDLs in the various mechanical states were observed. However, subtle adjustments in tissue hydration seemed to occur, particularly during stiffening.
[Show abstract][Hide abstract] ABSTRACT: Mutable collagenous tissues (MCTs) of echinoderms show reversible changes in tensile properties (mutability) that are initiated and modulated by the nervous system via the activities of cells known as juxtaligamental cells. The molecular mechanism underpinning this mechanical adaptability has still to be elucidated. Adaptable connective tissues are also present in mammals, most notably in the uterine cervix, in which changes in stiffness result partly from changes in the balance between matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs). There have been no attempts to assess the potential involvement of MMPs in the echinoderm mutability phenomenon, apart from studies dealing with a process whose relationship to the latter is uncertain. In this investigation we used the compass depressor ligaments (CDLs) of the sea-urchin Paracentrotus lividus. The effect of a synthetic MMP inhibitor - galardin - on the biomechanical properties of CDLs in different mechanical states ("standard", "compliant" and "stiff") was evaluated by dynamic mechanical analysis, and the presence of MMPs in normal and galardin-treated CDLs was determined semi-quantitatively by gelatin zymography. Galardin reversibly increased the stiffness and storage modulus of CDLs in all three states, although its effect was significantly lower in stiff than in standard or compliant CDLs. Gelatin zymography revealed a progressive increase in total gelatinolytic activity between the compliant, standard and stiff states, which was possibly due primarily to higher molecular weight components resulting from the inhibition and degradation of MMPs. Galardin caused no change in the gelatinolytic activity of stiff CDLs, a pronounced and statistically significant reduction in that of standard CDLs, and a pronounced, but not statistically significant, reduction in that of compliant CDLs. Our results provide evidence that MMPs may contribute to the variable tensility of the CDLs, in the light of which we provide an updated hypothesis for the regulatory mechanism controlling MCT mutability.
[Show abstract][Hide abstract] ABSTRACT: Although l-glutamate is the most widespread excitatory neurotransmitter in vertebrate and invertebrate nervous systems, there is only sparse evidence that it has this role in echinoderms. Following our previous finding that l-glutamate is widely distributed in the arms of the featherstar (crinoid echinoderm) Antedon mediterranea and initiates arm autotomy (defensive detachment), we now provide evidence of glutamatergic involvement in the control of the arm muscles of the same species using immunocytochemical and physiological methods. Immunofluorescence and immunoenzymatic techniques, which employed the same polyclonal antibody against l-glutamate conjugated to glutaraldehyde, revealed a high level of glutamate-like reactivity in the brachial muscles. By recording the mechanical responses of isolated arm pieces, we found that l-glutamate, l-aspartate and elevated [K(+)](o) induced rhythmic muscle contractions, while glycine, γ-aminobutyric acid, adrenaline and acetylcholine had either no, or no consistent, effect. The frequency and duration of the dominant component of the rhythmic contractions indicated that these may be responsible for the rhythmic activity of the arms that occurs during swimming and after autotomy. We conclude that it is highly likely that l-glutamate has at least a neuromodulatory role in the neural pathways controlling the brachial muscles of A. mediterranea.
[Show abstract][Hide abstract] ABSTRACT: Chondrosia reniformis is a common marine demosponge that shows striking tissue plasticity and unusual body deformability. This sponge can develop long and slender outgrowths extending from the parental body. According to some authors, this phenomenon, called “creeping”, can be related to asexual reproduction, atypical mechanisms of «localized» locomotion or passive response to environmental stress. Here we address this phenomenon by means of an interdisciplinary approach consisting of field survey, experimental field studies and experimental laboratory studies. During field survey and field experimental survey we observed that the instability of substratum is an important factor that trigs the beginning of creeping. The sponge size does not seem to be directly involved in the occurrence of the phenomenon. Specimens of Bergeggi (Ligurian Sea, northern Italy) show a high correlation between the creeping phenomenon and the sea temperature; this seems to support the hypothesis that the phenomenon is related to asexual reproduction, which is in its turn seasonally regulated by environmental temperature. In addition, experimental laboratory studies performed in different mechanical conditions on isolated samples of both ectosome and choanosome showed that temperature affects mesohyl mechanical properties: the lower is the temperature the stiffer is the mesohyl.
Full-text · Article · Oct 2012 · Journal of Experimental Marine Biology and Ecology
[Show abstract][Hide abstract] ABSTRACT: Although several authors have suggested a plausible involvement of steroids in the reproductive biology of echinoderms, their definitive role is still poorly understood. In this paper we focused on oestradiol (E2), whose presence and variations were previously revealed in different echinoderm tissues. The aim of this investigation was to provide further information on the scarcely known role of this hormone in the reproductive biology of sea urchins. We injected two different concentrations (5 ng ml−1 and 50 ng ml−1) of 17ß-oestradiol into specimens of the common Paracentrotus lividus for 10 weeks. The E2 treatment did not influence the maturation stage of the gonads and the development of the gametes; it caused a slight decrease in the gonad index and an increase in lipid content. Our present results suggest that E2 could have a function different from that reported for vertebrates and suggested for other echinoderms such as asteroids.
No preview · Article · Sep 2012 · Journal of the Marine Biological Association of the UK
[Show abstract][Hide abstract] ABSTRACT: In the recent decades, the importance of echinoderm endocrinology has increased because of the use of echinoderms as models for aquatic ecotoxicology and due to their evolutionary closeness to chordates. Nonetheless, apart from asteroids and echinoids, there is limited information available on the reproductive physiology of echinoderm groups, particularly crinoids. This investigation focused on the reproductive cycle of Antedon mediterranea and was intended to elucidate the reproductive pattern occurring in this species. We observed spawning throughout the year, though there were preferential months. The sex ratio was biased in favour of females. Possible correlations between steroid level variations and gonad maturity were also evaluated: testosterone and 17β-estradiol mean levels were higher at the beginning of gametogenesis and during vitellogenesis, suggesting their possible involvement in nutrient supply for developing gametes. This study should stimulate further work on steroids and steroid derivatives as ancestral hormones characteristic of the animal kingdom.
No preview · Article · Jul 2012 · Journal of Experimental Marine Biology and Ecology