The neuronal control of cardiac functions in Molluscs

Comparable properties of native K channels in the atrium and ventricle of snails

Mollusks, including snails, possess two chambered hearts. The heart and cardiomyocytes of snails have many similarities with those of mammals. Also, the biophysics and pharmacology of Ca, K, and Na ion channels resemble. Similar to mammals, in mollusks, the ventricular cardiomyocytes and K channels are often studied, which are selectively sensitive to antagonists such as 4-AP, E-4031, and TEA. Since the physiological properties of the ventricular cardiac cells of snails are well characterized, the enzymatically dissociated atrial cardiomyocytes of Cornu aspersum (Müller, 1774) were studied using the whole-cell patch-clamp technique for detailed comparisons with mice, Mus musculus. The incubation of tissues in a solution simultaneously containing two enzymes, collagenase and papain, enabled the isolation of single cells. Recordings in the atrial cardiomyocytes of snails revealed outward K+ currents closely resembling those of the ventricle. The latter was consistent, whether the voltage ramp or steps and long or short pulses were used. Interestingly, under identical conditions, the current waveforms of atrial cardiomyocytes in snails were similar to those of mice left ventricles, albeit the kinetics and the absence of inward rectifier K channel (IK1) activation. Therefore, the heart of mollusks could be used as a simple and accessible experimental model, particularly for pharmacology and toxicology studies.

Genome-wide identification and characteristic analysis of ETS gene family in blood clam Tegillarca granosa

BACKGROUND

ETS transcription factors, known as the E26 transformation-specific factors, assume a critical role in the regulation of various vital biological processes in animals, including cell differentiation, the cell cycle, and cell apoptosis. However, their characterization in mollusks is currently lacking.

RESULTS

The current study focused on a comprehensive analysis of the ETS genes in blood clam Tegillarca granosa and other mollusk genomes. Our phylogenetic analysis revealed the absence of the SPI and ETV subfamilies in mollusks compared to humans. Additionally, several ETS genes in mollusks were found to lack the PNT domain, potentially resulting in a diminished ability of ETS proteins to bind target genes. Interestingly, the bivalve ETS1 genes exhibited significantly high expression levels during the multicellular proliferation stage and in gill tissues. Furthermore, qRT-PCR results showed that Tg-ETS-14 (ETS1) is upregulated in the high total hemocyte counts (THC) population of T. granosa, suggesting it plays a significant role in stimulating hemocyte proliferation.

CONCLUSION

Our study significantly contributes to the comprehension of the evolutionary aspects concerning the ETS gene family, while also providing valuable insights into its role in fostering hemocyte proliferation across mollusks.

Comparative analysis of the cardiac structure and transcriptome of scallop and snail, perspectives on heart chamber evolution

The evolution of a two-chambered heart, with an atrium and a ventricle, has improved heart function in both deuterostomes (vertebrates) and some protostomes (invertebrates). Although studies have examined the unique structure and function of these two chambers, molecular comparisons are few and limited to vertebrates. Here, we focus on the two-chambered protostome heart of the mollusks, offering data that may provide a better understanding of heart evolution. Specifically, we asked if the atrium and ventricle differ at the molecular level in the mollusk heart. To do so, we examined two very different species, the giant African land snail (Lissachatina fulica) and the relatively small, aquatic yesso scallop (Mizuhopecten yessoensis), with the assumption that if they exhibited commonality these similarities would likely reflect those across the phylum. We found that, although the hearts of these two species differed histologically, their cardiac gene function enrichments were similar, as revealed by transcriptomic analysis. Furthermore, the atrium and ventricle in each species had distinct gene function clusters, suggesting an evolutionary differentiation of cardiac chambers in mollusks. Finally, to explore the relationship between vertebrate and invertebrate two-chambered hearts, we compared our transcriptomic data with published data from the zebrafish, a well-studied vertebrate model with a two-chambered heart. Our analysis indicated a functional similarity of ventricular genes between the mollusks and the zebrafish, suggesting that the ventricle was differentiated to achieve the same functions in invertebrates and vertebrates. As the first such study on protostomes, our findings offered initial insights into how the two-chambered heart arose, including a possible understanding of its occurrence in both protostomes and deuterostomes.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-023-00202-0.

Comparative Neuroanatomy of Pediveliger Larvae of Various Bivalves from the Sea of Japan

Here, we describe the nervous system structures from pediveligers of eight bivalve species (Callista brevisiphonata, Mactromeris polynyma, Crenomytilus grayanus, Kellia japonica, Mizuhopecten yessoensis, and Azumapecten farreri) with different modes of life in their adult stages, corresponding to the ecological niches that they occupy (burrowing, cemented, byssally attached, and mobile forms). We have identified neuromorphological features of the central and peripheral nervous systems in larval bivalves. We show that the unpaired sensory apical organ is still present in pediveligers along with the developing paired cerebral ganglia characteristic of an adult mollusk. Pediveligers have the pleural ganglia connected to the pedal ganglia via the pedal nerve cords and to the visceral ganglia via the lateral nerve cords. We have found a number of structures of the peripheral nervous system whose presence varies between pediveligers of different species. Mactromeris, Callista, and Pododesmus have 5-HT-immunopositive stomatogastric neurons, whereas the Yesso and Farrer's scallops have an FMRFamide-immunopositive enteric nervous system. The innervation of the anterior part of the velum is connected to a system of the apical organ and cerebral ganglia, and the innervation of the posterior part is connected to the visceral ganglia. Most differences in the structure of the peripheral elements of the nervous system are species-specific and weakly depend on the ecological niche that pediveligers occupy.

Toxic effects of four emerging pollutants on cardiac performance and associated physiological parameters of the thick-shell mussel (Mytilus coruscus)

Robust cardiac performance is critical for the health and even survival of an animal; however, it is sensitive to environmental stressors. At present, little is known about the cardiotoxicity of emerging pollutants to bivalve mollusks. Thus, in this study, the cardiotoxic effects of four emergent pollutants, carbamazepine (CBZ), bisphenol A (BPA), tetrabromobisphenol A (TBBPA), and tris(2-chloroethyl) phosphate (TCEP), on the thick-shell mussel, Mytilus coruscus, were evaluated by heartbeat monitoring and histological examinations. In addition, the impacts of these pollutants on parameters that closely related to cardiac function including neurotransmitters, calcium homeostasis, energy supply, and oxidative status were assessed. Our results demonstrated that 28-day exposure of the thick-shell mussel to these pollutants resulted in evident heart tissue lesions (indicated by hemocyte infiltration and myocardial fibrosis) and disruptions of cardiac performance (characterized by bradyrhythmia and arrhythmia). In addition to obstructing neurotransmitters and calcium homeostasis, exposure to pollutants also led to constrained energy supply and induced oxidative stress in mussel hearts. These findings indicate that although do differ somehow in their effects, these four pollutants may exert cardiotoxic impacts on mussels, which could pose severe threats to this important species and therefore deserves more attention.

Adam, amigo, brain, and K channel

Voltage-dependent K+ (Kv) channels are diverse, comprising the classical Shab - Kv2, Shaker - Kv1, Shal - Kv4, and Shaw - Kv3 families. The Shaker family alone consists of Kv1.1, Kv1.2, Kv1.3, Kv1.4, Kv1.5, Kv1.6, and Kv1.7. Moreover, the Shab family comprises two functional (Kv2.1 and Kv2.2) and several "silent" alpha subunits (Kv2.3, Kv5, Kv6, Kv8, and Kv9), which do not generate K current. However, e.g., Kv8.1, via heteromerization, inhibits outward currents of the same family or even that of Shaw. This property of Kv8.1 is similar to those of designated beta subunits or non-selective auxiliary elements, including ADAM or AMIGO proteins. Kv channels and, in turn, ADAM may modulate the synaptic long-term potentiation (LTP). Prevailingly, Kv1.1 and Kv1.5 are attributed to respective brain and heart pathologies, some of which may occur simultaneously. The aforementioned channel proteins are apparently involved in several brain pathologies, including schizophrenia and seizures.

A novel role for Teneurin C-terminal Associated Peptide (TCAP) in the regulation of cardiac activity in the Sydney rock oyster, Saccostrea glomerata

Teneurin C-terminal associated peptide (TCAP) is an ancient bioactive peptide that is highly conserved in metazoans. TCAP administration reduces cellular and behavioural stress in vertebrate and urochordate models, yet despite numerous studies in higher animals, there is limited knowledge of its role in invertebrates. In particular, there are no studies on TCAP's effects on the heart of any metazoan, which is a critical organ in the stress response. We used the Sydney rock oyster (SRO) as an invertebrate model to investigate a potential role for sroTCAP in regulating cardiac activity, including during stress. sroTCAP is localized to the neural innervation network of the SRO heart, and suggested binding with various heart proteins related to metabolism and stress, including SOD, GAPDH and metabotropic glutamate receptor. Intramuscular injection of sroTCAP (10 pmol) significantly altered the expression of heart genes that are known to regulate remodelling processes under different conditions, and modulated several gene families responsible for stress mitigation. sroTCAP (1 and 10 pmol) was shown to cause transient bradycardia (heart rate was reduced by up to 63% and for up to 40 min post-administration), indicative of an unstressed state. In summary, this study has established a role for a TCAP in the regulation of cardiac activity through modulation of physiological and molecular components associated with energy conservation, stress and adaptation. This represents a novel function for TCAP and may have implications for higher-order metazoans.

Role of the Neuroendocrine System of Marine Bivalves in Their Response to Hypoxia

Mollusks comprise one of the largest phylum of marine invertebrates. With their great diversity of species, various degrees of mobility, and specific behavioral strategies, they haveoccupied marine, freshwater, and terrestrial habitats and play key roles in many ecosystems. This success is explained by their exceptional ability to tolerate a wide range of environmental stresses, such as hypoxia. Most marine bivalvemollusksare exposed to frequent short-term variations in oxygen levels in their marine or estuarine habitats. This stressfactor has caused them to develop a wide variety of adaptive strategies during their evolution, enabling to mobilize rapidly a set of behavioral, physiological, biochemical, and molecular defenses that re-establishing oxygen homeostasis. The neuroendocrine system and its related signaling systems play crucial roles in the regulation of various physiological and behavioral processes in mollusks and, hence, can affect hypoxiatolerance. Little effort has been made to identify the neurotransmitters and genes involved in oxygen homeostasis regulation, and the molecular basis of the differences in the regulatory mechanisms of hypoxia resistance in hypoxia-tolerant and hypoxia-sensitive bivalve species. Here, we summarize current knowledge about the involvement of the neuroendocrine system in the hypoxia stress response, and the possible contributions of various signaling molecules to this process. We thusprovide a basis for understanding the molecular mechanisms underlying hypoxic stress in bivalves, also making comparisons with data from related studies on other species.

Functioning of K channels during sleep

The functioning of voltage-dependent K channels (Kv) may correlate with the physiological state of brain in organisms, including the sleep in Drosophila. Apparently, all major types of K currents are expressed in CNS of this model organism. These are the Shab-Kv2, Shaker-Kv1, Shal-Kv4, and Shaw-Kv3 α subunits and can be deciphered by patch-clamp technique. Although it is plausible that some of these channels may play a prevailing role in sleep or wakefulness, several of recent data are not conclusive. It needs to be defined that indeed the frequency of action potentials in large ventral lateral pacemaker neurons is either higher or lower during the morning or night because of an increased Kv3 and Kv4 currents, respectively. The outcomes of dynamic-clamp approach in combination with electrophysiology in insects are unreliable in contrast to those in mammalian neurons. Since the addition of virtual Kv conductance during any Zeitgeber time should not significantly alter the resting membrane potential. This review explains the Drosophila sleep behavior based on neural activity with respect to K current-driven action potential rate.

Probability that there is a mammalian counterpart of cardiac clock in insects

Whether or not the hyperpolarization-activated cyclic nucleotide-gated nonselective cation channel (HCN or funny current I_f ) is involved in pacemaking - recurrent heartbeat, it is attributed to electrical activities in all excitable cells, including those of invertebrates. In latter group of animals prevailingly the electrical signals and function of heart in terms of chrono- and inotropy are elucidated. Although in simpler models including insects experimental outcomes are reproducible and robust, involvement of "cardiac clock" mechanism in pacemaking is not conclusive. In this assay, the mechanisms of heartbeat are synthesized by focused comparisons between insect and mammalian hearts.

Variable Environments in an Upwelling System Trigger Differential Thermal Sensitivity in a Low Intertidal Chiton

Environmental variability in coastal oceans associated with upwelling dynamics probably is one of the most pervasive forces affecting the physiological performance of marine life. As the environmental temperature is the abiotic factor with major incidence in the physiology and ecology of marine ectotherms, the abrupt temperature changes in upwelling systems could generate important variations in these organisms’ functional processes. The relationship between ambient temperature and physiological performance can be described through a thermal performance curve (TPC). The parameters of this curve usually show geographic variation usually is in accordance with the predictions of the climate variability hypothesis (CVH), which states that organisms inhabiting more variable environments should have broader ranges of environmental tolerance in order to cope with the fluctuating environmental conditions they experience. Here we study the effect generated by the environmental variability in an active upwelling zone on the physiological performance of the marine ectotherm Achanthopleura echinata. In particular, we compared the parameters of the TPC and the metabolic rate of two populations of A. echinata, one found in high semi-permanent upwelling (Talcaruca), while the other is situated in an adjacent area with seasonal upwelling (Los Molles) and therefore more stable environmental conditions. Our results show that: (1) oxygen consumption increases with body size and this effect is more significant in individuals from the Talcaruca population, (2) optimal temperature, thermal breadth, upper critical limit and maximum performance were higher in the population located in the area of high environmental heterogeneity and (3) individuals from Talcaruca showed greater variance in optimal temperature, thermal breadth, upper critical limit but not in maximum performance. Although it is clear that a variable environment affects the thermal physiology of organisms, expanding their tolerance ranges and generating energy costs in the performance of individuals, it is relevant to note that upwelling systems are multifactorial phenomena where the rise of water masses modifies not only temperature, but also decreases O2, pH, and increases pCO2 which in turn could modify metabolism and TPC.

Inactivation of Native K Channels

We have experimented with isolated cardiomyocytes of mollusks Helix. During the whole-cell patch-clamp recordings of K⁺ currents a considerable decrease in amplitude was observed upon repeated voltage steps at 0.96 Hz. For these experiments, ventricular cells were depolarized to identical + 20 mV from a holding potential of - 50 mV. The observed spontaneous inhibition of outward currents persisted in the presence of 4-aminopyridine, tetraethylammonium chloride or E-4031, the selective class III antiarrhythmic agent that blocks HERG channels. Similar tendency was retained when components of currents sensitive to either 4-AP or TEA were mathematically subtracted. Waveforms of currents sensitive to 1 and 10 micromolar concentration of E-4031 were distinct comprising prevailingly those activated during up to 200 ms pulses. The outward current activated by a voltage ramp at 60 mV x s^-1 rate revealed an inward rectification around + 20 mV. This feature closely resembles those of the mammalian cardiac delayed rectifier I_Kr.

Low concentrations of oxazepam induce feeding and molecular changes in Radix balthica juveniles

Psychotropics, especially benzodiazepines, are commonly prescribed worldwide. Poorly eliminated at wastewater treatment plants, they belong to a group of emerging contaminants. Due to their interaction with the GABA_A receptor, they may affect the function of the nervous system of non-target organisms, such as aquatic organisms. The toxicity of oxazepam, a very frequently detected benzodiazepine in continental freshwater, has been largely studied in aquatic vertebrates over the last decade. However, its effects on freshwater non-vertebrates have received much less attention. We aimed to evaluate the long-term effects of oxazepam on the juvenile stage of a freshwater gastropod widespread in Europe, Radix balthica. Juveniles were exposed for a month to environmentally-relevant concentrations of oxazepam found in rivers (0.8 μg/L) and effluents (10 μg/L). Three main physiological functions were studied: feeding, growth, and locomotion. Additionally, gene expression analysis was performed to provide insights into toxicity mechanisms. There was a strong short-term activation of the feeding rate at low concentration, whereas the high dose resulted in long-term inhibition of food intake. A significant decrease in mortality rate was observed in juveniles exposed to the lowest dose. Shell growth and locomotor activity did not appear to be affected by oxazepam. Transcriptomic analysis revealed global over-expression of genes involved in the nervous regulation of the feeding, digestive, and locomotion systems after oxazepam exposure. The molecular analysis also revealed a possible interference of animal manipulation with the molecular effects induced by oxazepam exposure. Overall, these results improve our understanding of the effects of the psychoactive drug oxazepam on an aquatic mollusc gastropod.

Distribution of Molecules Related to Neurotransmission in the Nervous System of the Mussel Crenomytilus grayanus

In bivalves neurotransmitters are involved in a variety of behaviors, but their diversity and distribution in the nervous system of these organisms remains somewhat unclear. Here, we first examined immunohistochemically the distributions of neurons containing different neurotransmitters, neuropeptides, and related enzymes, as well as the proliferative status of neurons in the ganglia of the mussel Crenomytilus grayanus. H-Phe-Met-Arg-Phe-NH2 (FMRFamide), choline acetyltransferase (ChAT), γ-aminobutyric acid (GABA) and tyrosine hydroxylase (TH) were found to be expressed by neurons in all the ganglia, whereas serotonin (5-HT) neurons were found only in the cerebropleural and pedal, but not visceral ganglia. Moreover, incubation of living mussels in the presence of a 5-HT precursor (5-HTP) confirmed the absence of 5-HT-containing neurons from the visceral ganglia, indicating that the "serotonin center" of the visceral nervous system is located in the cerebral ganglia. Furthermore, immunostaining of molecules related to neurotransmission together with α-acetylated tubulin demonstrated that this cytoskeletal protein may be a potential pan-neuronal marker in bivalves. Adult mussel neurons do not proliferate, but a population of proliferating PCNA-LIP cells which do not express any of the neurotransmitters examined, perhaps glia cells, was detected in the ganglia. These novel findings suggest that the nervous system of bivalves contains a broad variety of signal molecules most likely involved in the regulation of different physiological and behavioral processes. In addition, proliferating cells may maintain and renew glial cells and neurons throughout the lives of bivalves.

Vortex Dynamics in Trabeculated Embryonic Ventricles

Proper heart morphogenesis requires a delicate balance between hemodynamic forces, myocardial activity, morphogen gradients, and epigenetic signaling, all of which are coupled with genetic regulatory networks. Recently both in vivo and in silico studies have tried to better understand hemodynamics at varying stages of veretebrate cardiogenesis. In particular, the intracardial hemodynamics during the onset of trabeculation is notably complex—the inertial and viscous fluid forces are approximately equal at this stage and small perturbations in morphology, scale, and steadiness of the flow can lead to significant changes in bulk flow structures, shear stress distributions, and chemical morphogen gradients. The immersed boundary method was used to numerically simulate fluid flow through simplified two-dimensional and stationary trabeculated ventricles of 72, 80, and 120 h post fertilization wild type zebrafish embryos and ErbB2-inhibited embryos at seven days post fertilization. A 2D idealized trabeculated ventricular model was also used to map the bifurcations in flow structure that occur as a result of the unsteadiness of flow, trabeculae height, and fluid scale (Re). Vortex formation occurred in intertrabecular regions for biologically relevant parameter spaces, wherein flow velocities increased. This indicates that trabecular morphology may alter intracardial flow patterns and hence ventricular shear stresses and morphogen gradients. A potential implication of this work is that the onset of vortical (disturbed) flows can upregulate Notch1 expression in endothelial cells in vivo and hence impacts chamber morphogenesis, valvulogenesis, and the formation of the trabeculae themselves. Our results also highlight the sensitivity of cardiac flow patterns to changes in morphology and blood rheology, motivating efforts to obtain spatially and temporally resolved chamber geometries and kinematics as well as the careful measurement of the embryonic blood rheology. The results also suggest that there may be significant changes in shear signalling due to morphological and mechanical variation across individuals and species.

Limulus and heart rhythm

Great interest in the comparative physiology of hearts and their functions in Animalia has emerged with classic papers on Limulus polyphemus and mollusks. The recurrent cardiac activity-heart rate-is the most important physiological parameter and when present the kardia (Greek) is vital to the development of entire organs of the organisms in the animal kingdom. Extensive studies devoted to the regulation of cardiac rhythm in invertebrates have revealed that the basics of heart physiology are comparable to mammals. The hearts of invertebrates also beat spontaneously and are supplied with regulatory nerves: either excitatory or inhibitory or both. The distinct nerves and the source of excitation/inhibition at the level of single neurons are described for many invertebrate genera. The vertebrates and a majority of invertebrates have myogenic hearts, whereas the horseshoe crab L. polyphemus and a few other animals have a neurogenic cardiac rhythm. Nevertheless, the myogenic nature of heartbeat is precursor, because the contraction of native and stem-cell-derived cardiomyocytes does occur in the absence of any neural elements. Even in L. polyphemus, the heart rhythm is myogenic at embryonic stages.

H+ channels in embryonic Biomphalaria glabrata cell membranes: Putative roles in snail host-schistosome interactions

The human blood fluke Schistosoma mansoni causes intestinal schistosomiasis, a widespread neglected tropical disease. Infection of freshwater snails Biomphalaria spp. is an essential step in the transmission of S. mansoni to humans, although the physiological interactions between the parasite and its obligate snail host that determine success or failure are still poorly understood. In the present study, the B. glabrata embryonic (Bge) cell line, a widely used in vitro model for hemocyte-like activity, was used to investigate membrane properties, and assess the impact of larval transformation proteins (LTP) on identified ion channels. Whole-cell patch clamp recordings from Bge cells demonstrated that a Zn2+-sensitive H+ channel serves as the dominant plasma membrane conductance. Moreover, treatment of Bge cells with Zn2+ significantly inhibited an otherwise robust production of reactive oxygen species (ROS), thus implicating H+ channels in the regulation of this immune function. A heat-sensitive component of LTP appears to target H+ channels, enhancing Bge cell H+ current over 2-fold. Both Bge cells and B. glabrata hemocytes express mRNA encoding a hydrogen voltage-gated channel 1 (HVCN1)-like protein, although its function in hemocytes remains to be determined. This study is the first to identify and characterize an H+ channel in non-neuronal cells of freshwater molluscs. Importantly, the involvement of these channels in ROS production and their modulation by LTP suggest that these channels may function in immune defense responses against larval S. mansoni.

Addictive neurons

Since the reward center is considered to be the area tegmentalis ventralis of the hypothalamus, logically its neurons could mainly be responsible for addiction. However, the literature asserts that almost any neurons of CNS can respond to one or another addictive compound. Obviously not only addictive nicotine, but also alcohol, amphetamine, cannabis, cocaine, heroin and morphine may influence dopaminergic cells alone in VTA. Moreover, paradoxically some of these drugs ameliorate symptoms, counterbalance syndromes, cure diseases and improve health, not only those related to the CNS and in adults, but also almost all other organs and in children, e.g. epilepsy.

Osmoregulated Chloride Currents in Hemocytes from Mytilus galloprovincialis

We investigated the biophysical properties of the transport mediated by ion channels in hemocytes from the hemolymph of the bivalve Mytilus galloprovincialis. Besides other transporters, mytilus hemocytes possess a specialized channel sensitive to the osmotic pressure with functional properties similar to those of other transport proteins present in vertebrates. As chloride fluxes may play an important role in the regulation of cell volume in case of modifications of the ionic composition of the external medium, we focused our attention on an inwardly-rectifying voltage-dependent, chloride-selective channel activated by negative membrane potentials and potentiated by the low osmolality of the external solution. The chloride channel was slightly inhibited by micromolar concentrations of zinc chloride in the bath solution, while the antifouling agent zinc pyrithione did not affect the channel conductance at all. This is the first direct electrophysiological characterization of a functional ion channel in ancestral immunocytes of mytilus, which may bring a contribution to the understanding of the response of bivalves to salt and contaminant stresses.

Predicting the physiological response of Tivela stultorum hearts with digoxin from cardiac parameters using artificial neural networks

Multi-layer perceptron artificial neural networks (MLP-ANNs) were used to predict the concentration of digoxin needed to obtain a cardio-activity of specific biophysical parameters in Tivela stultorum hearts. The inputs of the neural networks were the minimum and maximum values of heart contraction force, the time of ventricular filling, the volume used for dilution, heart rate and weight, volume, length and width of the heart, while the output was the digoxin concentration in dilution necessary to obtain a desired physiological response. ANNs were trained, validated and tested with the dataset of the in vivo experiment results. To select the optimal network, predictions for all the dataset for each configuration of ANNs were made, a maximum 5% relative error for the digoxin concentration was set and the diagnostic accuracy of the predictions made was evaluated. The double-layer perceptron had a barely higher performance than the single-layer perceptron; therefore, both had a good predictive ability. The double-layer perceptron was able to obtain the most accurate predictions of digoxin concentration required in the hearts of T. stultorum using MLP-ANNs.

Nerve-granular cell communication in the atrium of the snail Achatina achatina occurs via the cardioexcitatory transmitters serotonin and FMRFamide

In the present study, the anatomical association and functional interaction between nerve fibres and granular cells in the atrium of the snail Achatina achatina are investigated using a combination of scanning electron microscopy (SEM), pharmacological and immunofluorescence techniques. The SEM studies support a close anatomical association of axons with granular cells and new features of surface morphology are revealed. Pharmacological experiments showed that both serotonin and FMRFamide were able to induce degranulation of granular cells and the release of cysteine-rich atrial secretory protein. Serotonin- and FMRFamide-immunoreactive nerve fibres were observed at variable distances from granular cells, ranging from close contact to distances as far as the diameter of a muscle bundle. These results suggest that serotonin and FMRFamide play a role as paracrine excitatory transmitters in nerve-to-granular cell communication.

Catecholaminergic System of Invertebrates: Comparative and Evolutionary Aspects in Comparison With the Octopaminergic System

In this review we examined the catecholaminergic system of invertebrates, starting from protists and getting to chordates. Different techniques used by numerous researchers revealed, in most examined phyla, the presence of catecholamines dopamine, noradrenaline, and adrenaline or of the enzymes involved in their synthesis. The catecholamines are generally linked to the nervous system and they can act as neurotransmitters, neuromodulators, and hormones; moreover they play a very important role as regards the response to a large number of stress situations. Nevertheless, in some invertebrate phyla belonging to Protostoma, the monoamine octopamine is the main biogenic amine. The presence of catecholamines in some protists suggests a role as intracellular or interorganismal signaling molecules and an ancient origin of their synthetic pathways. The catecholamines appear also involved in the regulation of bioluminescence and in the control of larval development and metamorphosis in some marine invertebrate phyla.

Cysteine-Rich Atrial Secretory Protein from the Snail Achatina achatina: Purification and Structural Characterization

Despite extensive studies of cardiac bioactive peptides and their functions in molluscs, soluble proteins expressed in the heart and secreted into the circulation have not yet been reported. In this study, we describe an 18.1-kDa, cysteine-rich atrial secretory protein (CRASP) isolated from the terrestrial snail Achatina achatina that has no detectable sequence similarity to any known protein or nucleotide sequence. CRASP is an acidic, 158-residue, N-glycosylated protein composed of eight alpha-helical segments stabilized with five disulphide bonds. A combination of fold recognition algorithms and ab initio folding predicted that CRASP adopts an all-alpha, right-handed superhelical fold. CRASP is most strongly expressed in the atrium in secretory atrial granular cells, and substantial amounts of CRASP are released from the heart upon nerve stimulation. CRASP is detected in the haemolymph of intact animals at nanomolar concentrations. CRASP is the first secretory protein expressed in molluscan atrium to be reported. We propose that CRASP is an example of a taxonomically restricted gene that might be responsible for adaptations specific for terrestrial pulmonates.

Identification of Mytilus edulis genetic regulators during early development

Understanding the mechanisms that enable growth and survival of an organism while driving it to the full range of its adaptation is fundamental to the issues of biodiversity and evolution, particularly regarding global climatic changes. Here we report the Illumina RNA-sequencing (RNA-seq) and de novo assembly of the blue mussel Mytilus edulis transcriptome during early development. This study is based on high-throughput data, which associates genome-wide differentially expressed transcript (DET) patterns with early activation of developmental processes. Approximately 50,383 high-quality contigs were assembled. Over 8000 transcripts were associated with functional proteins from public databases. Coding and non-coding genes served to design customized microarrays targeting every developmental stage, which encompass major transitions in tissue organization. Consequently, multi-processing pattern exploration protocols applied to 3633 DETs helped discover 12 unique coordinated eigengenes supposedly implicated in various physiological and morphological changes that larvae undergo during early development. Moreover, dynamic Bayesian networks (DBNs) provided key insights to understand stage-specific molecular mechanisms activated throughout ontogeny. In addition, delayed and contemporaneous interactions between DETs were coerced with 16 relevant regulators that interrelated in non-random genetic regulatory networks (GRNs). Genes associated with mechanisms of neural and muscular development have been characterized and further included in dynamic networks necessary in growth and functional morphology. This is the first large-scale study being dedicated to M. edulis throughout early ontogeny. Integration between RNA-seq and microarray data enabled a high-throughput exploration of hidden processes essential in growth and survival of microscopic mussel larvae. Our integrative approach will support a holistic understanding of systems biology and will help establish new links between environmental assessment and functional development of marine bivalves.