Growth-controlling molluscan neurons produce the precursor of an insulin-related peptide

Cumulative phylogenetic, sequence and structural analysis of Insulin superfamily proteins provide unique structure-function insights

The insulin superfamily proteins (ISPs), in particular, insulin, IGFs and relaxin proteins are key modulators of animal physiology. They are known to have evolved from the same ancestral gene and have diverged into proteins with varied sequences and distinct functions, but maintain a similar structural architecture stabilized by highly conserved disulphide bridges. The recent surge of sequence data and the structures of these proteins prompted a need for a comprehensive analysis, which connects the evolution of these sequences (427 sequences) in the light of available functional and structural information including representative complex structures of ISPs with their cognate receptors. This study reveals (a) unusually high sequence conservation of IGFs (>90 % conservation in 184 sequences) and provides a possible structure-based rationale for such high sequence conservation; (b) provides an updated definition of the receptor-binding signature motif of the functionally diverse relaxin family members (c) provides a probable non-canonical C-peptide cleavage site in a few insulin sequences. The high conservation of IGFs appears to represent a classic case of resistance to sequence diversity exerted by physiologically important interactions with multiple partners. We also propose a probable mechanism for C-peptide cleavage in a few distinct insulin sequences and redefine the receptor-binding signature motif of the relaxin family. Lastly, we provide a basis for minimally modified insulin mutants with potential therapeutic application, inspired by concomitant changes observed in other insulin superfamily protein members supported by molecular dynamics simulation.

The mega-evolution of life with its three memory systems depends on sender-receiver communication and problem-solving. A narrative review

It should be the ultimate goal of any theory of evolution to delineate the contours of an integrative system to answer the question: How does life (in all its complexity) evolve (which can be called mega-evolution)? But how to plausibly define 'life'? My answer (1994-2023) is: 'life' sounds like a noun, but denotes an activity, and thus is a verb. Life (L) denotes nothing else than the total sum (∑) of all acts of communication (transfer of information) (C) executed by any type of senders-receivers at all their levels (up to at least 15) of compartmental organization: L = ∑C. The 'communicating compartment' is better suited to serve as the universal unit of structure, function and evolution than the cell, the smallest such unit. By paying as much importance to communication activity as to the Central Dogma of molecular biology, a wealth of new insights unfold. The major ones are as follows. (1) Living compartments have not only a genetic memory (DNA), but also a still enigmatic cognitive and an electrical memory system (and thus a triple memory system). (2) Complex compartments can have up to three types of progeny: genetic descendants/children, pupils/learners and electricians. (3) Of particular importance to adaptation, any act of communication is a problem-solving act because all messages need to be decoded. Hence through problem-solving that precedes selection, life itself is the driving force of its own evolution (a very clever but counterintuitive and unexpected logical deduction). Perhaps, this is the 'vital force' philosopher and Nobel laureate (in 1927) Henri Bergson searched for but did not find.

Molecular and structural analysis of Hdh-MIRP3 and its impact on reproductive regulation in female Pacific abalone, Haliotis discus hannai

Molluscan insulin-related peptides (MIRP) play a crucial role in various biological processes, including reproduction and larval development in mollusk species. To investigate the involvement of MIRP in the ovarian development of Pacific abalone (Haliotis discus hannai), the Hdh-MIRP3 was cloned from cerebral ganglion (CG). Hdh-MIRP3 cDNA was 993 bp long, encoded a 13.22 kDa peptide, comprising 118 amino acids. Fluorescence in situ hybridization confirmed the localization of Hdh-MIRP3 in the CG and ovary. Molecular docking revealed that Hdh-MIRP3 binds to the N-terminal region of Hdh-IRP-R. Tissue expression analysis showed the highest Hdh-MIRP3 expression in the CG, followed by ovarian tissue. Hdh-MIRP3 expression was significantly upregulated in the CG and ovary during the ripe stage of seasonal ovarian development and in effective accumulative temperature conditioned abalone. Furthermore, siRNA silencing of Hdh-MIRP3 significantly downregulated the expression of four reproduction-related genes, including Hdh-GnRH, Hdh-GnRH-R, Hdh-IRP-R, and Hdh-VTG in both the CG and ovary, and Hdh-MIRP3 as well. These results indicate that Hdh-MIRP3 acts as a regulator of ovarian development in Pacific abalone. Additionally, expression analysis indicated that Hdh-MIRP3 plays a role in embryonic and larval development. Overall, the present findings elucidate the role of Hdh-MIRP3 in reproductive development in female Pacific abalone.

Insulin-like Peptide Receptor (ILPR) in the Cuttlefish Sepiella japonica: Characterization, Expression, and Regulation of Reproduction

Insulin-like peptide receptor (ILPR) can effectively regulate ovarian development in invertebrates, but its effect in cuttlefish has not been reported. We isolated and characterized a ILPR gene from Sepiella japonica, referred to as SjILPR. This gene displayed significant homologies to Octopus bimaculoides ILPR, and contained all typical features of insulin receptors and tyrosine kinase domain structure. SjILPR is expressed in all detected tissues, with the highest expression in the ovary. During ovarian development stages, its expression levels in the ovary, pancreas, and liver were correlated to the female reproductive cycle. After the silencing of SjILPR in vivo, comparative transcriptome analysis identified 4314 differentially expressed genes (DEGs) in the injected group, including 2586 down-regulated genes and 1728 up-regulated genes. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses revealed that 832 DEGs were assigned to 222 pathways, many pathways of which were related to gonadal development. Four down-regulated genes relevant to ovarian development (Vitellogenin 1, Vitellogenin 2, Cathepsin L1-like, and Follistatin) were selected to confirm the accuracy of RNA-seq data by qRT-PCR. These results showed that SjILPR might regulate ovarian development to control reproduction by affecting the expression of the relevant genes in female S. japonica.

Characterization of Insulin-like Peptide (ILP) and Its Potential Role in Ovarian Development of the Cuttlefish Sepiella japonica

The insulin-like peptide (ILP) family is well known for regulating reproduction in invertebrates, while its role in mollusks remains largely unknown. In this study, we first isolated and characterized the ILP gene in the cuttlefish Sepiella japonica. The full-length SjILP cDNA obtained was 926 bp and encoded a precursor protein of 161 amino acids. The precursor protein consisted of a signal peptide, a B chain, a C-peptide, and an A chain. It possessed the typical features of ILP proteins, including two cleavage sites (KR) and eight conserved cysteines. To define the function of SjILP, the expression of SjILP in different tissues and ovarian development stages were analyzed using qRT-PCR. SjILP was mainly expressed in the ovary, and its gene expression correlated with ovarian development. Furthermore, silencing SjILP using RNA interference (RNAi) dramatically decreased the expression levels of four ovarian-development-related genes (vitellogenin1, vitellogenin2, cathepsin L1-like, and follistatin). These data suggest the critical role of SjILP in the regulation of ovarian development in S. japonica.

Insulin and Memory in Invertebrates

Insulin and insulin-like peptides (ILP) help to maintain glucose homeostasis, whereas insulin-like growth factor (IGF) promotes the growth and differentiation of cells in both vertebrates and invertebrates. It is sometimes difficult to distinguish between ILP and IGF in invertebrates, however, because in some cases ILP has the same function as IGF. In the present review, therefore, we refer to these peptides as ILP/IGF signaling (IIS) in invertebrates, and discuss the role of IIS in memory formation after classical conditioning in invertebrates. In the arthropod Drosophila melanogaster, IIS is involved in aversive olfactory memory, and in the nematode Caenorhabditis elegans, IIS controls appetitive/aversive response to NaCl depending on the duration of starvation. In the mollusk Lymnaea stagnalis, IIS has a critical role in conditioned taste aversion. Insulin in mammals is also known to play an important role in cognitive function, and many studies in humans have focused on insulin as a potential treatment for Alzheimer’s disease. Although analyses of tissue and cellular levels have progressed in mammals, the molecular mechanisms, such as transcriptional and translational levels, of IIS function in cognition have been far advanced in studies using invertebrates. We anticipate that the present review will help to pave the way for studying the effects of insulin, ILPs, and IGFs in cognitive function across phyla.

Novel Human Insulin Isoforms and Cα-Peptide Product in Islets of Langerhans and Choroid Plexus

Human insulin (INS) gene diverged from the ancestral genes of invertebrate and mammalian species millions of years ago. We previously found that mouse insulin gene (Ins2) isoforms are expressed in brain choroid plexus (ChP) epithelium cells, where insulin secretion is regulated by serotonin and not by glucose. We further compared human INS isoform expression in postmortem ChP and islets of Langerhans. We uncovered novel INS upstream open reading frame isoforms and their protein products. In addition, we found a novel alternatively spliced isoform that translates to a 74-amino acid (AA) proinsulin containing a shorter 19-AA C-peptide sequence, herein designated Cα-peptide. The middle portion of the conventional C-peptide contains β-sheet (GQVEL) and hairpin (GGGPG) motifs that are not present in Cα-peptide. Islet amyloid polypeptide (IAPP) is not expressed in ChP, and its amyloid formation was inhibited in vitro more efficiently by Cα-peptide than by C-peptide. Of clinical relevance, the ratio of the 74-AA proinsulin to proconvertase-processed Cα-peptide was significantly increased in islets from type 2 diabetes mellitus autopsy donors. Intriguingly, 100 years after the discovery of insulin, we found that INS isoforms are present in ChP from insulin-deficient autopsy donors.

Identification and localization of growth factor genes in the sea cucumber, Holothuria scabra

The sea cucumber Holothuria scabra is both an economically important species in Asian countries and an emerging experimental model for research studies in regeneration and medicinal bioactives. Growth factors and their receptors are known to be key components that guide tissue repair and renewal, yet validation of their presence in H. scabra has not been established. We performed a targeted in silico search of H. scabra transcriptome data to elucidate conserved growth factor family and receptor genes. In total, 42 transcripts were identified, of which 9 were validated by gene cloning and sequencing. The H. scabra growth factor genes, such as bone morphogenetic protein 2A (BMP 2A), bone morphogenetic protein 5-like (BMP5-like), neurotrophin (NT) and fibroblast growth factor 18 (FGF18), were selected for further analyses, including phylogenetic comparison and spatial gene expression using RT-PCR and in situ hybridization. Expression of all genes investigated were widespread in multiple tissues. However, BMP 2A, BMP5-like and NT were found extensively in the radial nerve cord cells, while FGF18 was highly expressed in connective tissue layer of the body wall. Our identification and expression analysis of the H. scabra growth factor genes provided the molecular information of growth factors in this species which may ultimately complement the research in regenerative medicine.

Crosstalk between dopamine and insulin signaling in growth control of the oyster

Neuroendocrine hormones such as dopamine and insulin/insulin-like peptides play indispensable roles in growth regulation of animals, while the interplay between dopamine and insulin signaling pathways remains largely unknown in invertebrates. In the present study, we showed that tyrosine hydroxylase (TH), the rate-limiting enzyme of dopamine synthesis, was highly expressed in all tissues of the fast-growing oysters, and gradually increased with the development, which indicated the potential role of dopamine in growth regulation. Incubated with dopamine hydrochloride and insulin-like peptide recombinant proteins in vitro induced the expression of TH, suggesting a mutual regulatory relationship between insulin and dopamine signaling. Fasting and re-feeding experiments confirmed the role of TH in food intake regulation, also provide a clue about the potential regulatory relationship between the FoxO and TH. Further luciferase assay experiment confirmed that FoxO was involved in transcriptional regulation of TH gene through binding to its specific promoter region. This work provided insights into the crosstalk between dopamine and insulin signaling in growth control of mollusks.

Transcriptome analysis provides genome annotation and expression profiles in the central nervous system of Lymnaea stagnalis at different ages

BACKGROUND

The pond snail, Lymnaea stagnalis (L. stagnalis), has served as a valuable model organism for neurobiology studies due to its simple and easily accessible central nervous system (CNS). L. stagnalis has been widely used to study neuronal networks and recently gained popularity for study of aging and neurodegenerative diseases. However, previous transcriptome studies of L. stagnalis CNS have been exclusively carried out on adult L. stagnalis only. As part of our ongoing effort studying L. stagnalis neuronal growth and connectivity at various developmental stages, we provide the first age-specific transcriptome analysis and gene annotation of young (3 months), adult (6 months), and old (18 months) L. stagnalis CNS.

RESULTS

Using the above three age cohorts, our study generated 55-69 millions of 150 bp paired-end RNA sequencing reads using the Illumina NovaSeq 6000 platform. Of these reads, ~ 74% were successfully mapped to the reference genome of L. stagnalis. Our reference-based transcriptome assembly predicted 42,478 gene loci, of which 37,661 genes encode coding sequences (CDS) of at least 100 codons. In addition, we provide gene annotations using Blast2GO and functional annotations using Pfam for ~ 95% of these sequences, contributing to the largest number of annotated genes in L. stagnalis CNS so far. Moreover, among 242 previously cloned L. stagnalis genes, we were able to match ~ 87% of them in our transcriptome assembly, indicating a high percentage of gene coverage. The expressional differences for innexins, FMRFamide, and molluscan insulin peptide genes were validated by real-time qPCR. Lastly, our transcriptomic analyses revealed distinct, age-specific gene clusters, differentially expressed genes, and enriched pathways in young, adult, and old CNS. More specifically, our data show significant changes in expression of critical genes involved in transcription factors, metabolisms (e.g. cytochrome P450), extracellular matrix constituent, and signaling receptor and transduction (e.g. receptors for acetylcholine, N-Methyl-D-aspartic acid, and serotonin), as well as stress- and disease-related genes in young compared to either adult or old snails.

CONCLUSIONS

Together, these datasets are the largest and most updated L. stagnalis CNS transcriptomes, which will serve as a resource for future molecular studies and functional annotation of transcripts and genes in L. stagnalis.

Evidence from oyster suggests an ancient role for Pdx in regulating insulin gene expression in animals

Hox and ParaHox genes encode transcription factors with similar expression patterns in divergent animals. The Pdx (Xlox) homeobox gene, for example, is expressed in a sharp spatial domain in the endodermal cell layer of the gut in chordates, echinoderms, annelids and molluscs. The significance of comparable gene expression patterns is unclear because it is not known if downstream transcriptional targets are also conserved. Here, we report evidence indicating that a classic transcriptional target of Pdx1 in vertebrates, the insulin gene, is a likely direct target of Pdx in Pacific oyster adults. We show that one insulin-related gene, cgILP, is co-expressed with cgPdx in oyster digestive tissue. Transcriptomic comparison suggests that this tissue plays a similar role to the vertebrate pancreas. Using ATAC-seq and ChIP, we identify an upstream regulatory element of the cgILP gene which shows binding interaction with cgPdx protein in oyster hepatopancreas and demonstrate, using a cell culture assay, that the oyster Pdx can act as a transcriptional activator through this site, possibly in synergy with NeuroD. These data argue that a classic homeodomain-target gene interaction dates back to the origin of Bilateria.

In vertebrates insulin is a direct transcriptional target of Pdx: the same is true in Pacific oysters and the authors show insulin-related gene, cgILP, is co-expressed with cgPdx in oyster digestive tissue, showing this gene interaction dates back to the origin of Bilateria.

Insulin-Like Peptide Receptor-Mediated Signaling Pathways Orchestrate Regulation of Growth in the Pacific Oyster (Crassostrea gigas), as Revealed by Gene Expression Profiles

The involvement of insulin/insulin-like growth factor signaling (IIS) pathways in the growth regulation of marine invertebrates remains largely unexplored. In this study, we used a fast-growing Pacific oyster (Crassostrea gigas) variety “Haida No.1” as the material with which to unravel the role of IIS systems in growth regulation in oysters. Systematic bioinformatics analyses allowed us to identify major components of the IIS signaling pathway and insulin-like peptide receptor (ILPR)-mediated signaling pathways, including PI3K-AKT, RAS-MAPK, and TOR, in C. gigas. The expression levels of the major genes in IIS and its downstream signaling pathways were significantly higher in “Haida No.1” than in wild oysters, suggesting their involvement in the growth regulation of C. gigas. The expression profiles of IIS and its downstream signaling pathway genes were significantly altered by nutrient abundance and culture temperature. These results suggest that the IIS signaling pathway coupled with the ILPR-mediated signaling pathways orchestrate the regulation of energy metabolism to control growth in Pacific oysters.

Sticky problems: extraction of nucleic acids from molluscs

Traditional molecular methods and omics-techniques across molluscan taxonomy increasingly inform biology of Mollusca. Recovery of DNA and RNA for such studies is challenged by common biological properties of the highly diverse molluscs. Molluscan biomineralization, adhesive structures and mucus involve polyphenolic proteins and mucopolysaccharides that hinder DNA extraction or copurify to inhibit enzyme-catalysed molecular procedures. DNA extraction methods that employ the detergent hexadecyltrimethylammoniumbromide (CTAB) to remove these contaminants importantly facilitate molecular-level study of molluscs. Molluscan pigments may stain DNA samples and interfere with spectrophotometry, necessitating gel electrophoresis or fluorometry for accurate quantification. RNA can reliably be extracted but the 'hidden break' in 28S rRNA of molluscs (like most protostomes) causes 18S and 28S rRNA fragments to co-migrate electrophoretically. This challenges the standard quality control based on the ratio of 18S and 28S rRNA, developed for deuterostome animals. High-AT content in molluscan rRNA prevents the effective purification of polyadenylated mRNA. Awareness of these matters aids the continuous expansion of molecular malacology, enabling work also with museum specimens and next-generation sequencing, with the latter imposing unprecedented demands on DNA quality. Alternative methods to extract nucleic acids from molluscs are available from literature and, importantly, from communications with others who study the molecular biology of molluscs. This article is part of the Theo Murphy meeting issue 'Molluscan genomics: broad insights and future directions for a neglected phylum'.

Untangling the effect of insulin action on brain mitochondria and metabolism

The regulation of energy homeostasis is controlled by the brain and, besides requiring high amounts of energy, it relies on functional insulin/insulin-like growth factor (IGF)-1 signalling in the central nervous system. This energy is mainly provided by mitochondria in form of ATP. Thus, there is an intricate interplay between mitochondrial function and insulin/IGF-1 action to enable functional brain signalling and, accordingly, propagate a healthy metabolism. To adapt to different nutritional conditions, the brain is able to sense the current energy status via mitochondrial and insulin signalling-dependent pathways and exerts an appropriate metabolic response. However, regional, cell type and receptor-specific consequences of this interaction occur and are linked to diverse outcomes such as altered nutrient sensing, body weight regulation or even cognitive function. Impairments of this cross-talk can lead to obesity and glucose intolerance and are linked to neurodegenerative diseases, yet they also induce a self-sustainable, dysfunctional 'metabolic triangle' characterised by insulin resistance, mitochondrial dysfunction and inflammation in the brain. The identification of causal factors deteriorating insulin action, mitochondrial function and concomitantly a signature of metabolic stress in the brain is of utter importance to offer novel mechanistic insights into development of the continuously rising prevalence of non-communicable diseases such as type 2 diabetes and neurodegeneration. This review aims to determine the effect of insulin action on brain mitochondrial function and energy metabolism. It precisely outlines the interaction and differences between insulin action, insulin-like growth factor (IGF)-1 signalling and mitochondrial function; distinguishes between causality and association; and reveals its consequences for metabolism and cognition. We hypothesise that an improvement of at least one signalling pathway can overcome the vicious cycle of a self-perpetuating metabolic dysfunction in the brain present in metabolic and neurodegenerative diseases.

Insulin-like and mimetic molecules from non-mammalian organisms: potential relevance for drug discovery

Insulin was first discovered in extracts of vertebrate pancreas during a focused search for a therapy for diabetes. Subsequent efforts to discover and isolate a similar active principle from yeast and plants driven by the hope to identify insulin-like/mimetic molecules with critical advantages in the pharmacokinetic profile and expenditure of production compared to authentic human insulin were not successful. As a consequence, it has generally been assumed that hormones evolved exclusively during course of the evolution of vertebrate endocrine organs, implying a rather recent origin. Concomitantly, the existence and physiological role of vertebrate hormones in lower multi- and unicellular eukaryotes have remained a rather controversial subject over decades, albeit there is some evidence that hormones and hormone-binding proteins resembling those of vertebrates are expressed in fungi and yeast. Past and recent findings on the existence of insulin-like and mimetic materials, such as the glucose tolerance factor, in lower eukaryotes, in particular Neurospora crassa and yeast, will be presented. These data provide further evidence for the provocative view that the evolutionary roots of the vertebrate endocrine system may be far more ancient than is generally believed and that the identification and characterisation of insulin-like/mimetic molecules from lower eukaryotes may be useful for future drug discovery efforts.

RNAi-mediated knock-down of the dopamine beta-hydroxylase gene changes growth of razor clams

Dopamine beta-hydroxylase (DβH) plays an essential role in the synthesis of catecholamines (CA) in neuroendocrine networks. In the razor clam, Sinonovacula constricta a novel gene for DβH (ScDβH-α) was identified that belongs to the copper type II ascorbate-dependent monooxygenase family. Expression analysis revealed ScDβH-α gene transcripts were abundant in the liver and expressed throughout development. Knock-down of ScDβH-α in adult clams using siRNA caused a reduction in the growth rate compared to control clams. Reduced growth was associated with strong down-regulation of gene transcripts for the growth-related factors, platelet derived growth factors A (PDGF-A) (P < 0.001) 24 h after ScDβH-α knock-down, vascular endothelial growth factor (VEGF1) (P < 0.001) and platelet derived growth factor B (PDGF-B-2) (P < 0.001) 24 h and 48 h after ScDβH-α knock-down and transforming growth factor beta (TGF-β1) (P < 0.001) 48 h and 72 h after ScDβH-α knock-down. Taken together the results suggest that the novel ScDβH-α gene through its role in CA synthesis is involved in growth regulation in the razor clam and possibly other bivalves.

Arthropod IGF, relaxin and gonadulin, putative orthologs of Drosophila insulin-like peptides 6, 7 and 8, likely originated from an ancient gene triplication

BACKGROUND

Insects have several genes coding for insulin-like peptides and they have been particularly well studied in Drosophila. Some of these hormones function as growth hormones and are produced by the fat body and the brain. These act through a typical insulin receptor tyrosine kinase. Two other Drosophila insulin-like hormones are either known or suspected to act through a G-protein coupled receptor. Although insulin-related peptides are known from other insect species, Drosophila insulin-like peptide 8, one that uses a G-protein coupled receptor, has so far only been identified from Drosophila and other flies. However, its receptor is widespread within arthropods and hence it should have orthologs. Such putative orthologs were recently identified in decapods and have been called gonadulins.

METHODOLOGY

In an effort to identify gonadulins in other arthropods public genome assemblies and short-read archives from insects and other arthropods were explored for the presence of genes and transcripts coding insulin-like peptides and their putative receptors.

RESULTS

Gonadulins were detected in a number of arthropods. In those species for which transcriptome data from the gonads is available insect gonadulin genes are expressed in the ovaries and at least in some species also in the testes. In some insects differences in gonadulin expression in the ovary between actively reproducing and non-reproducing females differs more than 100-fold. Putative orthologs of Drosophila ilp 6 were also identified. In several non-Dipteran insects these peptides have C-terminally extensions that are alternatively spliced. The predicted peptides have been called arthropod insulin-like growth factors. In cockroaches, termites and stick insects genes coding for the arthropod insulin-like growth factors, gonadulin and relaxin, a third insulin-like peptide, are encoded by genes that are next to one another suggesting that they are the result of a local gene triplication. Such a close chromosomal association was also found for the arthropod insulin-like growth factor and gonadulin genes in spiders. Phylogenetic tree analysis of the typical insulin receptor tyrosine kinases from insects, decapods and chelicerates shows that the insulin signaling pathway evolved differently in these three groups. The G-protein coupled receptors that are related to the Drosophila ilp 8 receptor similarly show significant differences between those groups.

CONCLUSION

A local gene triplication in an early ancestor likely yielded three genes coding gonadulin, arthropod insulin-like growth factor and relaxin. Orthologs of these genes are now commonly present in arthropods and almost certainly include the Drosophila insulin-like peptides 6, 7 and 8.

The role of a new insulin-like peptide in the pearl oyster Pinctada fucata martensii

Pinctada fucata martensii, is an economically important marine bivalve species cultured for seawater pearls. At present, we know little about the molecular mechanisms of the insulin signalling pathway in this oyster. Herein, we cloned and analysed an insulin-like peptide (PfILP) and its signalling pathway-related genes. We detected their expression levels in different tissues and developmental stages. Recombinant PfILP protein was produced and found to significantly increase primary mantle cell activity and induce the expression of the proliferating cell nuclear antigen (PCNA) gene. PfILP could also regulate the 293T cell cycle by stimulating the S phase and inhibiting the G1 and G2 phases. Recombinant PfILP protein induced the expression of its signalling pathway-related genes in mantle cells. In vitro co-immunoprecipitation analysis showed that PfILP interacts with PfIRR. PfILP activated expression of the pfIRR protein, and also activated the mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K) pathways by stimulating phosphorylation of MAPK and AKT. Further analysis showed that PfILP up-regulated glycogen synthesis-related genes glycogen synthase kinase-3 beta (GSK-3β), protein phosphatase 1 (PP1) and glucokinase (GK) at the mRNA level, as well as the expression of the PP1 protein, and phosphorylation of GSK-3β. These results confirmed the presence of a conserved insulin-like signalling pathway in pearl oyster that is involved in cell activity, glycogen metabolism, and other physiological processes.

Snail defence responses to parasite infection: The Lymnaea stagnalis-Trichobilharzia szidati model

Lymnaea stagnalis is a common freshwater gastropod. Importantly, the snail serves as the intermediate host for more than one hundred species of digenetic trematodes, including the avian schistosome Trichobilharzia szidati, a causative agent of cercarial dermatitis in humans. Infection of L. stagnalis by T. szidati initiates a dynamic confrontation between the host and the parasite that culminates in immunocompatibility ensuring survival and development of larvae. Unfortunately, the molecular mechanisms determining this immunocompatibility remain poorly characterised. By employing a variety of immune elicitors, including chemical compounds, PAMPs and bacteria, research in the last two decades has elucidated some of the molecular processes that regulate the snail internal defence response such as haemocyte signalling pathways. These discoveries provide a framework for future studies of molecular interactions between T. szidati and L. stagnalis to help elucidate factors and mechanisms enabling transmission of schistosome parasites. Moreover, support from recently available next generation sequence data and CRISPR-enabled functional genomics should further enable L. stagnalis as an important model for comparative immunology and contribute to a more comprehensive understanding of immune functions in gastropod molluscs.

Lymnaea stagnalis as model for translational neuroscience research: From pond to bench

The purpose of this review is to illustrate how a reductionistic, but sophisticated, approach based on the use of a simple model system such as the pond snail Lymnaea stagnalis (L. stagnalis), might be useful to address fundamental questions in learning and memory. L. stagnalis, as a model, provides an interesting platform to investigate the dialog between the synapse and the nucleus and vice versa during memory and learning. More importantly, the "molecular actors" of the memory dialogue are well-conserved both across phylogenetic groups and learning paradigms, involving single- or multi-trials, aversion or reward, operant or classical conditioning. At the same time, this model could help to study how, where and when the memory dialog is impaired in stressful conditions and during aging and neurodegeneration in humans and thus offers new insights and targets in order to develop innovative therapies and technology for the treatment of a range of neurological and neurodegenerative disorders.

An immunohistochemical analysis of peptidergic neurons apparently associated with reproduction and growth in Biomphalaria alexandrina

Peptide hormones and neurotransmitters involved in reproduction and growth have been studied extensively in certain gastropod molluscs, such as Lymnaea stagnalis and Aplysia californica. The present study employs antisera that have been used to study peptidergic neurons in those species to probe the central nervous system of another gastropod, Biomphalaria alexandrina, an intermediate host of the parasitic trematode that causes schistosomiasis in humans. Whole mount preparations of central ganglia were stained immunohistochemically, and several populations of neurons appeared to be homologous to those forming the neuroendocrine axis that has been previously described in L. stagnalis. These cells include the caudodorsal cells and the light green and canopy cells, which produce hormones that regulate ovulation and growth, respectively. Other populations of cells containing APGWamide, FMRFamide and/or related peptides are consistent with ones that innervate the penis in L. stagnalis and other gastropods. Identification of neurons that might be responsible for the control of reproduction and growth in Biomphalaria provides an important initial step toward the development of novel methods of disease control and pest management directed toward reducing snail populations.

Monoamines, Insulin and the Roles They Play in Associative Learning in Pond Snails

Molluscan gastropods have long been used for studying the cellular and molecular mechanisms underlying learning and memory. One such gastropod, the pond snail Lymnaea stagnalis, exhibits long-term memory (LTM) following both classical and operant conditioning. Using Lymnaea, we have successfully elucidated cellular mechanisms of learning and memory utilizing an aversive classical conditioning procedure, conditioned taste aversion (CTA). Here, we present the behavioral changes following CTA training and show that the memory score depends on the duration of food deprivation. Then, we describe the relationship between the memory scores and the monoamine contents of the central nervous system (CNS). A comparison of learning capability in two different strains of Lymnaea, as well as the filial 1 (F1) cross from the two strains, presents how the memory scores are correlated in these populations with monoamine contents. Overall, when the memory scores are better, the monoamine contents of the CNS are lower. We also found that as the insulin content of the CNS decreases so does the monoamine contents which are correlated with higher memory scores. The present review deepens the relationship between monoamine and insulin contents with the memory score.

Data for evolutive analysis of insulin related peptides in bilaterian species

In bilaterian species, the amino acid sequence conservation between Insulin related peptides is relatively low except for the cysteine residues involved in the disulphide bonds. In the A chain, the conserved cystein residues are included in a signature motif. Investigating the variations in this motif would give insight into the phylogenetic history of the family. The table presented in this paper contains a large set of insulin-related peptides in bilateral phylogenetic groups (deuterostomian, ecdysozoan, lophotrochozoan). NCBI databases in silico wide screening combined with bibliographic researches provided a framework for identifying and categorising the structural characteristics of these insulin related peptides. The dataset includes NCBI IDs of each sequence with hyperlinks to FASTA format. Moreover, the structural type (α, β or γ), the A chain motif, the total number of cysteins, the C peptide cleavage mode and the potential additional domains (D or E) are specified for each sequence. The data are associated with the research article "Molecular evolution and functional characterisation of insulin-related peptides in molluscs: contributions of Crassostrea gigas genomic and transcriptomic-wide screening" [1]. The table presented here can be found at http://dx.doi.org/10.17632/w4gr8zcpk5.4#file-21c0f6a5-a3e3-4a15-86e0-e5a696458866.

Molecular evolution and functional characterisation of insulin related peptides in molluscs: Contributions of Crassostrea gigas genomic and transcriptomic-wide screening

Insulin Related Peptides (IRPs) belong to the insulin superfamily and possess a typical structure with two chains, B and A, linked by disulphide bonds. As the sequence conservation is usually low between members, IRPs are classified according to the number and position of their disulphide bonds. In molluscan species, the first IRPs identified, named Molluscan Insulin-related Peptides (MIPs), exhibit four disulphide bonds. The genomic and transcriptomic data screening in the Pacific oyster Crassostrea gigas (Mollusc, Bivalvia) allowed us to identify six IRP sequences belonging to three structural groups. Cg-MIP1 to 4 have the typical structure of MIPs with four disulphide bonds. Cg-ILP has three disulphide bonds like vertebrate Insulin-Like Peptides (ILPs). The last one, Cg-MILP7 has a significant homology with Drosophila ILP7 (DILP7) associated with two additional cysteines allowing the formation of a fourth disulphide bond. The phylogenetic analysis points out that ILPs may be the most ancestral form. Moreover, it appears that ILP7 orthologs are probably anterior to lophotrochozoa and ecdysozoa segregation. In order to investigate the diversity of physiological functions of the oyster IRPs, we combine in silico expression data, qPCR measurements and in situ hybridization. The Cg-ilp transcript, mainly detected in the digestive gland and in the gonadal area, is potentially involved in the control of digestion and gametogenesis. The expression of Cg-mip4 is mainly associated with the larval development. The Cg-mip transcript shared by the Cg-MIP1, 2 and 3, is mainly expressed in visceral ganglia but its expression was also observed in the gonads of mature males. This pattern suggested the key roles of IRPs in the control of sexual reproduction in molluscan species.

A central control circuit for encoding perceived food value

Hunger state can substantially alter the perceived value of a stimulus, even to the extent that the same sensory cue can trigger antagonistic behaviors. How the nervous system uses these graded perceptual shifts to select between opposed motor patterns remains enigmatic. Here, we challenged food-deprived and satiated Lymnaea to choose between two mutually exclusive behaviors, ingestion or egestion, produced by the same feeding central pattern generator. Decoding the underlying neural circuit reveals that the activity of central dopaminergic interneurons defines hunger state and drives network reconfiguration, biasing satiated animals toward the rejection of stimuli deemed palatable by food-deprived ones. By blocking the action of these neurons, satiated animals can be reconfigured to exhibit a hungry animal phenotype. This centralized mechanism occurs in the complete absence of sensory retuning and generalizes across different sensory modalities, allowing food-deprived animals to increase their perception of food value in a stimulus-independent manner to maximize potential calorific intake.

Identification and Characterization of Neuropeptides by Transcriptome and Proteome Analyses in a Bivalve Mollusc Patinopecten yessoensis

Neuropeptides play essential roles in regulation of reproduction and growth in marine molluscs. But their function in marine bivalves – a group of animals of commercial importance – is largely unexplored due to the lack of systematic identification of these molecules. In this study, we sequenced and analyzed the transcriptome of nerve ganglia of Yesso scallop Patinopecten yessoensis, from which 63 neuropeptide genes were identified based on BLAST and de novo prediction approaches, and 31 were confirmed by proteomic analysis using the liquid chromatography-tandem mass spectrometry (LC-MS/MS). Fifty genes encode known neuropeptide precursors, of which 20 commonly exist in bilaterians and 30 are protostome specific. Three neuropeptides that have not yet been reported in bivalves were identified, including calcitonin/DH31, lymnokinin and pleurin. Characterization of glycoprotein hormones, insulin-like peptides, allatostatins, RFamides, and some reproduction, cardioactivity or feeding related neuropeptides reveals scallop neuropeptides have conserved molluscan neuropeptide domains, but some (e.g., GPB5, APGWamide and ELH) are characterized with bivalve-specific features. Thirteen potentially novel neuropeptides were identified, including 10 that may also exist in other protostomes, and 3 (GNamide, LRYamide, and Vamide) that may be scallop specific. In addition, we found neuropeptides potentially related to scallop shell growth and eye functioning. This study represents the first comprehensive identification of neuropeptides in scallop, and would contribute to a complete understanding on the roles of various neuropeptides in endocrine regulation in bivalve molluscs.

Molecular identification of an insulin growth factor binding protein (IGFBP) and its potential role in an insulin-like peptide system of the pearl oyster, Pinctada fucata

Insulin-like growth factors (IGFs) play critical roles in regulating metabolism, growth, and reproduction in invertebrates. IGF binding proteins (IGFBPs) serve as major regulators of IGF activity and regulate endocrine system. In the present study, the full-length cDNA of an igfbp was identified from the pearl oyster, Pinctada fucata, using expressed sequence tag (EST) sequence. The 1124bp Pfigfbp cDNA contains a 465bp open reading frame (ORF) encoding a putative protein of 154 amino acids, a 5'-untranslated region (UTR) of 238bp, and a 3'-UTR of 394bp (not including polyA+). Multiple sequence alignment of the deduced IB domain sequences revealed that twelve conserved Cys and ILP binding site in PfIGFBP were well aligned with human IGFBPs1-7, Mizuhopecten yessoensis IGFBP5 and Eriocheir sinensis IGFBP7. Gene expression analysis indicated that Pfigfbp mRNA was expressed in all the tissues and developmental stages examined, with a higher level in the foot than in other tissues and a higher level in the polar body stage and 32-cell stage than in the other stages. Pfigfbp and PfILP (insulin-like peptide) mRNA levels significantly increased in the digestive gland after feeding, while levels were dramatically reduced during a week of food deprivation and increased upon refeeding. In vitro experiments indicated that Pfigfbp mRNA expression in mantle cells was affected by insulin/IGFs (IGF-I, IGF-II). Our data suggests that Pfigfbp may be involved in endocrine signaling in P. fucata via the regulation of insulin-like peptide signaling.

Neuroendocrine-Immune Systems Response to Environmental Stressors in the Cephalopod Octopus vulgaris

Under a continuous changing environment, animals are challenged with stresses and stimuli which demanding adaptation at behavioral and physiological levels. The adaptation strategies are finely regulated by animal nervous, endocrine, and immune systems. Although it's been established by now the usage of integrative approach to the study the endocrine and nervous systems (neuroendocrine), yet our understanding of how they cooperate with the immune system remains far from complete. The possible role that immune system plays as a component of the network has only been recognized recently. Octopus vulgaris is an important member of cephalopods and is considered as a model species, with considerable information about the neuroendocrine and immune systems. In the current review, we anticipate to shed light on the complexity and cross talk among the three systems and how they cooperate in setting physiological response to stresses-stimuli in O. vulgaris as a target species and primary example.

Adipokinetic hormones and their G protein-coupled receptors emerged in Lophotrochozoa

Most multicellular animals belong to two evolutionary lineages, the Proto– and Deuterostomia, which diverged 640–760 million years (MYR) ago. Neuropeptide signaling is abundant in animals belonging to both lineages, but it is often unclear whether there exist evolutionary relationships between the neuropeptide systems used by proto- or deuterostomes. An exception, however, are members of the gonadotropin-releasing hormone (GnRH) receptor superfamily, which occur in both evolutionary lineages, where GnRHs are the ligands in Deuterostomia and GnRH-like peptides, adipokinetic hormone (AKH), corazonin, and AKH/corazonin-related peptide (ACP) are the ligands in Protostomia. AKH is a well-studied insect neuropeptide that mobilizes lipids and carbohydrates from the insect fat body during flight. In our present paper, we show that AKH is not only widespread in insects, but also in other Ecdysozoa and in Lophotrochozoa. Furthermore, we have cloned and deorphanized two G protein-coupled receptors (GPCRs) from the oyster Crassostrea gigas (Mollusca) that are activated by low nanomolar concentrations of oyster AKH (pQVSFSTNWGSamide). Our discovery of functional AKH receptors in molluscs is especially significant, because it traces the emergence of AKH signaling back to about 550 MYR ago and brings us closer to a more complete understanding of the evolutionary origins of the GnRH receptor superfamily.

PfIRR Interacts with HrIGF-I and Activates the MAP-kinase and PI3-kinase Signaling Pathways to Regulate Glycogen Metabolism in Pinctada fucata

The insulin-induced mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K) pathways are major intracellular signaling modules and conserved among eukaryotes that are known to regulate diverse cellular processes. However, they have not been investigated in the mollusk species Pinctada fucata. Here, we demonstrate that insulin-related peptide receptor of P. fucata (pfIRR) interacts with human recombinant insulin-like growth factor I (hrIGF-I), and stimulates the MAPK and PI3K signaling pathways in P. fucata oocytes. We also show that inhibition of pfIRR by the inhibitor PQ401 significantly attenuates the basal and hrIGF-I-induced phosphorylation of MAPK and PI3K/Akt at amino acid residues threonine 308 and serine 473. Furthermore, our experiments show that there is cross-talk between the MAPK and PI3K/Akt pathways, in which MAPK kinase positively regulates the PI3K pathway, and PI3K positively regulates the MAPK cascade. Intramuscular injection of hrIGF-I stimulates the PI3K and MAPK pathways to increase the expression of pfirr, protein phosphatase 1, glucokinase, and the phosphorylation of glycogen synthase, decreases the mRNA expression of glycogen synthase kinase-3 beta, decreases glucose levels in hemocytes, and increases glycogen levels in digestive glands. These results suggest that the MAPK and PI3K pathways in P. fucata transmit the hrIGF-I signal to regulate glycogen metabolism.

Neuropeptidome of the Cephalopod Sepia officinalis: Identification, Tissue Mapping, and Expression Pattern of Neuropeptides and Neurohormones during Egg Laying

Cephalopods exhibit a wide variety of behaviors such as prey capture, communication, camouflage, and reproduction thanks to a complex central nervous system (CNS) divided into several functional lobes that express a wide range of neuropeptides involved in the modulation of behaviors and physiological mechanisms associated with the main stages of their life cycle. This work focuses on the neuropeptidome expressed during egg-laying through de novo construction of the CNS transcriptome using an RNAseq approach (Illumina sequencing). Then, we completed the in silico analysis of the transcriptome by characterizing and tissue-mapping neuropeptides by mass spectrometry. To identify neuropeptides involved in the egg-laying process, we determined (1) the neuropeptide contents of the neurohemal area, hemolymph (blood), and nerve endings in mature females and (2) the expression levels of these peptides. Among the 38 neuropeptide families identified from 55 transcripts, 30 were described for the first time in Sepia officinalis, 5 were described for the first time in the animal kingdom, and 14 were strongly overexpressed in egg-laying females as compared with mature males. Mass spectrometry screening of hemolymph and nerve ending contents allowed us to clarify the status of many neuropeptides, that is, to determine whether they were neuromodulators or neurohormones.

Function of insulin in snail brain in associative learning

Insulin is well known as a hormone regulating glucose homeostasis across phyla. Although there are insulin-independent mechanisms for glucose uptake in the mammalian brain, which had contributed to a perception of the brain as an insulin-insensitive organ for decades, the finding of insulin and its receptors in the brain revolutionized the concept of insulin signaling in the brain. However, insulin's role in brain functions, such as cognition, attention, and memory, remains unknown. Studies using invertebrates with their open blood-vascular system have the promise of promoting a better understanding of the role played by insulin in mediating/modulating cognitive functions. In this review, the relationship between insulin and its impact on long-term memory (LTM) is discussed particularly in snails. The pond snail Lymnaea stagnalis has the ability to undergo conditioned taste aversion (CTA), that is, it associatively learns and forms LTM not to respond with a feeding response to a food that normally elicits a robust feeding response. We show that molluscan insulin-related peptides are up-regulated in snails exhibiting CTA-LTM and play a key role in the causal neural basis of CTA-LTM. We also survey the relevant literature of the roles played by insulin in learning and memory in other phyla.

Identification, evolution and expression of an insulin-like peptide in the cephalochordate Branchiostoma lanceolatum

Insulin is one of the most studied proteins since it is central to the regulation of carbohydrate and fat metabolism in vertebrates and its expression and release are disturbed in diabetes, the most frequent human metabolic disease worldwide. However, the evolution of the function of the insulin protein family is still unclear. In this study, we present a phylogenetic and developmental analysis of the Insulin Like Peptide (ILP) in the cephalochordate amphioxus. We identified an ILP in the European amphioxus Branchiostoma lanceolatum that displays structural characteristics of both vertebrate insulin and Insulin-like Growth Factors (IGFs). Our phylogenetic analysis revealed that amphioxus ILP represents the sister group of both vertebrate insulin and IGF proteins. We also characterized both temporal and spatial expression of ILP in amphioxus. We show that ilp is highly expressed in endoderm and paraxial mesoderm during development, and mainly expressed in the gut of both the developing embryo and adult. We hypothesize that ILP has critical implications in both developmental processes and metabolism and could display IGF- and insulin-like functions in amphioxus supporting the idea of a common ancestral protein.

Reproduction-related genes in the pearl oyster genome

Molluscan reproduction has been a target of biological research because of the various reproductive strategies that have evolved in this phylum. It has also been studied for the development of fisheries technologies, particularly aquaculture. Although fundamental processes of reproduction in other phyla, such as vertebrates and arthropods, have been well studied, information on the molecular mechanisms of molluscan reproduction remains limited. The recently released draft genome of the pearl oyster Pinctada fucata provides a novel and powerful platform for obtaining structural information on the genes and proteins involved in bivalve reproduction. In the present study, we analyzed the pearl oyster draft genome to screen reproduction-related genes. Analysis was mainly conducted for genes reported from other molluscs for encoding orthologs of reproduction-related proteins in other phyla. The gene search in the P. fucata gene models (version 1.1) and genome assembly (version 1.0) were performed using Genome Browser and BLAST software. The obtained gene models were then BLASTP searched against a public database to confirm the best-hit sequences. As a result, more than 40 gene models were identified with high accuracy to encode reproduction-related genes reported for P. fucata and other molluscs. These include vasa, nanos, doublesex- and mab-3-related transcription factor, 5-hydroxytryptamine (5-HT) receptors, vitellogenin, estrogen receptor, and others. The set of reproduction-related genes of P. fucata identified in the present study constitute a new tool for research on bivalve reproduction at the molecular level.

Identification of putative insulin-like peptides and components of insulin signaling pathways in parasitic platyhelminths by the use of genome-wide screening

No endogenous insulin-like peptides in parasitic flatworms have been reported. Insulin receptors from flukes and tapeworms have been shown to interact directly with the host-derived insulin molecule, which suggests the exploitation of host-derived insulin. In this study, a strategy of genome-wide searches followed by comprehensive analyses of strictly conserved features of the insulin family was used to demonstrate the presence of putative insulin-like peptides in the genomes of six tapeworms and two flukes. In addition, whole insulin signaling pathways were annotated on a genome-wide scale. Two putative insulin-like peptide genes in each genome of tapeworms and one insulin-like peptide gene in each genome of flukes were identified. The comprehensive analyses revealed that all of these peptides showed the common features shared by other members of the insulin family, and the phylogenetic analysis implied a putative gene duplication event in the Cestoda during the evolution of insulin-like peptide genes. The quantitative expression analysis and immunolocalization results suggested a putative role of these peptides in reproduction. Entire sets of major components of the classic insulin signaling pathway were successfully identified, suggesting that this pathway in parasitic flatworms might also regulate many other important biological activities. We believe that the identification of the insulin-like peptides gives us a better understanding of the insulin signaling pathway in these parasites, as well as host-parasite interactions.

Consolidation of long-term memory by insulin in Lymnaea is not brought about by changing the number of insulin receptors

The pond snail Lymnaea stagnalis learns taste aversion and consolidates it into long-term memory (LTM). This is referred to as conditioned taste aversion (CTA). The superfusion of molluscan insulin-related peptides (MIPs) over the isolated snail brain causes a long-term enhancement of synaptic input between the cerebral giant cell and the B1 buccal motor neuron. This enhancement is hypothesized to underlie CTA. The synaptic enhancement caused by the superfusion of MIPs can be blocked by the application of human insulin receptor antibody, which recognizes the extracellular domain of human insulin receptor and acts as an antagonist even for MIP receptors. An injection of the human insulin receptor antibody into the abdominal cavity of trained snails blocks the consolidation process leading to LTM, even though the snails acquire taste aversion. Here, we examined whether or not taste-aversion training changes the mRNA expression level of MIP receptor in the snail brain and found that it does not. This result, taken together with previous findings, suggest that the MIPs’ effect on synaptic function in the snail brain is attributable to a change in the MIP concentration, and not to a change in the mRNA expression level of MIP receptor, which is thought to reflect the number of MIP receptors.

Involvement of insulin-like peptide in long-term synaptic plasticity and long-term memory of the pond snail Lymnaea stagnalis

The pond snail Lymnaea stagnalis is capable of learning taste aversion and consolidating this learning into long-term memory (LTM) that is called conditioned taste aversion (CTA). Previous studies showed that some molluscan insulin-related peptides (MIPs) were upregulated in snails exhibiting CTA. We thus hypothesized that MIPs play an important role in neurons underlying the CTA-LTM consolidation process. To examine this hypothesis, we first observed the distribution of MIP II, a major peptide of MIPs, and MIP receptor and determined the amounts of their mRNAs in the CNS. MIP II was only observed in the light green cells in the cerebral ganglia, but the MIP receptor was distributed throughout the entire CNS, including the buccal ganglia. Next, when we applied exogenous mammalian insulin, secretions from MIP-containing cells or partially purified MIPs, to the isolated CNS, we observed a long-term change in synaptic efficacy (i.e., enhancement) of the synaptic connection between the cerebral giant cell (a key interneuron for CTA) and the B1 motor neuron (a buccal motor neuron). This synaptic enhancement was blocked by application of an insulin receptor antibody to the isolated CNS. Finally, injection of the insulin receptor antibody into the snail before CTA training, while not blocking the acquisition of taste aversion learning, blocked the memory consolidation process; thus, LTM was not observed. These data suggest that MIPs trigger changes in synaptic connectivity that may be correlated with the consolidation of taste aversion learning into CTA-LTM in the Lymnaea CNS.

Insulin analog with additional disulfide bond has increased stability and preserved activity

Insulin is a key hormone controlling glucose homeostasis. All known vertebrate insulin analogs have a classical structure with three 100% conserved disulfide bonds that are essential for structural stability and thus the function of insulin. It might be hypothesized that an additional disulfide bond may enhance insulin structural stability which would be highly desirable in a pharmaceutical use. To address this hypothesis, we designed insulin with an additional interchain disulfide bond in positions A10/B4 based on Cα-Cα distances, solvent exposure, and side-chain orientation in human insulin (HI) structure. This insulin analog had increased affinity for the insulin receptor and apparently augmented glucodynamic potency in a normal rat model compared with HI. Addition of the disulfide bond also resulted in a 34.6°C increase in melting temperature and prevented insulin fibril formation under high physical stress even though the C-terminus of the B-chain thought to be directly involved in fibril formation was not modified. Importantly, this analog was capable of forming hexamer upon Zn addition as typical for wild-type insulin and its crystal structure showed only minor deviations from the classical insulin structure. Furthermore, the additional disulfide bond prevented this insulin analog from adopting the R-state conformation and thus showing that the R-state conformation is not a prerequisite for binding to insulin receptor as previously suggested. In summary, this is the first example of an insulin analog featuring a fourth disulfide bond with increased structural stability and retained function.

RNAseq analysis of the parasitic nematode Strongyloides stercoralis reveals divergent regulation of canonical dauer pathways

The infectious form of many parasitic nematodes, which afflict over one billion people globally, is a developmentally arrested third-stage larva (L3i). The parasitic nematode Strongyloides stercoralis differs from other nematode species that infect humans, in that its life cycle includes both parasitic and free-living forms, which can be leveraged to investigate the mechanisms of L3i arrest and activation. The free-living nematode Caenorhabditis elegans has a similar developmentally arrested larval form, the dauer, whose formation is controlled by four pathways: cyclic GMP (cGMP) signaling, insulin/IGF-1-like signaling (IIS), transforming growth factor β (TGFβ) signaling, and biosynthesis of dafachronic acid (DA) ligands that regulate a nuclear hormone receptor. We hypothesized that homologous pathways are present in S. stercoralis, have similar developmental regulation, and are involved in L3i arrest and activation. To test this, we undertook a deep-sequencing study of the polyadenylated transcriptome, generating over 2.3 billion paired-end reads from seven developmental stages. We constructed developmental expression profiles for S. stercoralis homologs of C. elegans dauer genes identified by BLAST searches of the S. stercoralis genome as well as de novo assembled transcripts. Intriguingly, genes encoding cGMP pathway components were coordinately up-regulated in L3i. In comparison to C. elegans, S. stercoralis has a paucity of genes encoding IIS ligands, several of which have abundance profiles suggesting involvement in L3i development. We also identified seven S. stercoralis genes encoding homologs of the single C. elegans dauer regulatory TGFβ ligand, three of which are only expressed in L3i. Putative DA biosynthetic genes did not appear to be coordinately regulated in L3i development. Our data suggest that while dauer pathway genes are present in S. stercoralis and may play a role in L3i development, there are significant differences between the two species. Understanding the mechanisms governing L3i development may lead to novel treatment and control strategies.

Parasitic nematodes infect over one billion people worldwide and cause many diseases, including strongyloidiasis, filariasis, and hookworm disease. For many of these parasites, including Strongyloides stercoralis, the infectious form is a developmentally arrested and long-lived thirdstage larva (L3i). Upon encountering a host, L3i quickly resume development and mature into parasitic adults. In the free-living nematode Caenorhabditis elegans, a similar developmentally arrested third-stage larva, known as the dauer, is regulated by four key cellular mechanisms. We hypothesized that similar cellular mechanisms control L3i arrest and activation. Therefore, we used deep-sequencing technology to characterize the S. stercoralis transcriptome (RNAseq), which allowed us to identify S. stercoralis homologs of components of these four mechanisms and examine their temporal regulation. We found similar temporal regulation between S. stercoralis and C. elegans for components of two mechanisms, but dissimilar temporal regulation for two others, suggesting conserved as well as novel modes of developmental regulation for L3i. Understanding L3i development may lead to novel control strategies as well as new treatments for strongyloidiasis and other diseases caused by parasitic nematodes.

Culture of cells from two life stages of Schistosoma mansoni

The ability to culture continuously proliferating cell lines of various organisms in vitro has provided numerous advantages in experimental approaches toward the understanding of basic biology and disease. Although in vitro approaches are common in many disciplines, this methodology has proven difficult to exploit in the study of helminthic parasites. A major cause of parasitic disease, particularly in tropical countries, is the trematode Schistosoma mansoni. We have developed in vitro techniques that allow the long term maintenance of cell cultures from two stages of the life cycle of this organism, associated with its mammalian and the molluscan hosts. We have developed quantitative assays of cell survival and proliferation in our culture systems, and obtained evidence for limited proliferation in vitro. Although the cultures we have achieved thus far are useful for many kinds of experiments in vitro, development of continuously proliferating cell lines remains our goal.

In silico cloning of genes encoding neuropeptides, neurohormones and their putative G-protein coupled receptors in a spider mite

The genome of the spider mite was prospected for the presence of genes coding neuropeptides, neurohormones and their putative G-protein coupled receptors. Fifty one candidate genes were found to encode neuropeptides or neurohormones. These include all known insect neuropeptides and neurohormones, with the exception of sulfakinin, corazonin, neuroparsin and PTTH. True orthologs of adipokinetic hormone (AKH) were neither found, but there are three genes encoding peptides similar in structure to both AKH and the AKH-corazonin-related peptide. We were also unable to identify the precursors for pigment dispersing factor (PDF) or the recently discovered trissin. However, the spider mite probably does have such genes, as we found their putative receptors. A novel arthropod neuropeptide gene was identified that shows similarity to previously described molluscan neuropeptide genes and was called EFLamide. A total of 65 putative neuropeptide GPCR genes were also identified, of these 58 belong to the A-family and 7 to the B-family. Phylogenetic analysis showed that 50 of them are closely related to insect GPCRs, which allowed the identification of their putative ligand in 39 cases with varying degrees of certainty. Other spider mite GPCRs however have no identifiable orthologs in the genomes of the four holometabolous insect species best analyzed. Whereas some of the latter have orthologs in hemimetabolous insect species, crustaceans or ticks, for others such arthropod homologs are currently unknown.

Identification of Ras, Pten and p70S6K homologs in the Pacific oyster Crassostrea gigas and diet control of insulin pathway

Insulin pathways were demonstrated from invertebrates to vertebrates to be involved in the regulation of numerous processes including storage metabolism and reproduction. In addition, insulin system may integrate variations of environmental conditions like dietary restrictions. In the Pacific oyster Crassostrea gigas, reproductive and storage compartments are closely intricated in the gonadal area and their respective development was found to be dependant of trophic conditions. For these reasons, C. gigas is an original and interesting model for investigating the role of insulin control in the balance between storage and reproduction and the integration of environmental parameters. On the basis of sequence conservation, we identified three potential elements of the oyster insulin pathway, Ras, Pten and p70S6K and we investigated their expression levels in various tissues. In the gonadal area, we used laser microdissection in order to precise the targeted contribution of insulin signaling to the restoration of storage tissue and to the control of vitellogenesis. Food deprivation during gametogenesis reinitiation stage led to reduced proliferations of gonia and also to modulate insulin signal by transcriptional activation of insulin pathway elements.

Conditioned taste aversion dependent regulation of amygdala gene expression

The present experiments investigated gene expression in the amygdala following contingent taste/LiCl treatment that supports development of conditioned taste aversion (CTA). The use of whole genome chips and stringent data set filtering led to the identification of 168 genes regulated by CTA compared to non-contingent LiCl treatment that does not support CTA learning. Seventy-six of these genes were eligible for network analysis. Such analysis identified "behavior" as the top biological function, which was represented by 15 of the 76 genes. These genes included several neuropeptides, G protein-coupled receptors, ion channels, kinases, and phosphatases. Subsequent qRT-PCR analyses confirmed changes in mRNA expression for 5 of 7 selected genes. We were able to demonstrate directionally consistent changes in protein level for 3 of these genes; insulin 1, oxytocin, and major histocompatibility complex class I-C. Behavioral analyses demonstrated that blockade of central insulin receptors produced a weaker CTA that was less resistant to extinction. Together, these results support the notion that we have identified downstream genes in the amygdala that contribute to CTA learning.

Neuropeptide evolution: neurohormones and neuropeptides predicted from the genomes of Capitella teleta and Helobdella robusta

Genes encoding neurohormones and neuropeptide precursors were identified in the genomes of two annelids, the leech Helobdella robusta and the polychaete worm Capitella teleta. Although no neuropeptides have been identified from these two species and relatively few neuropeptides from annelids in general, 43 and 35 such genes were found in Capitella and Helobdella, respectively. The predicted peptidomes of these two species are similar to one another and also similar to those of mollusks, particular in the case of Capitella. Helobdella seems to have less neuropeptide genes than Capitella and it lacks the glycoprotein hormones bursicon and GPA2/GPB5; in both cases the genes coding the two subunits as well as the genes coding their receptors are absent from its genome. In Helobdella several neuropeptide genes are duplicated, thus it has five NPY genes, including one pseudogene, as well as four genes coding Wwamides (allatostatin B). Genes coding achatin, allatotropin, allatostatin C, conopressin, FFamide, FLamide, FMRFamide, GGRFamide, GnRH, myomodulin, NPY, pedal peptides, RGWamide (a likely APGWamide homolog), RXDLamide, VR(F/I)amide, WWamide were found in both species, while genes coding cerebrin, elevenin, GGNG, LFRWamide, LRFYamide, luqin, lymnokinin and tachykinin were only found in Capitella.

Neurohormones and neuropeptides encoded by the genome of Lottia gigantea, with reference to other mollusks and insects

The Lottia gigantea genome was prospected for the presence of genes coding neuropeptides and neurohormones. Four genes code insulin-related peptides: two genes code molluscan insulin-like growth hormones, one gene an insulin very similar to vertebrate insulin, and the fourth a peptide related to drosophila insulin-like peptide 7. Four other genes encode the cysteine-knot proteins GPA2/GPB5 and bursicon/parabursicon. Another 37 genes code for precursors of the following neuropeptides: achatin, APGWamide, allatostatin C, allatotropin, buccalin (perhaps an allatostatin A homolog), cerebrin, CCAP, conopressin, elevenin (the predicted neuropeptide made by abdominal neuron 11 in Aplysia), egg laying hormone (two genes), enterin, feeding circuit activating neuropeptide (FCAP), FFamide, FMRFamide, GGNG, a GnRH-like peptide, the newly discovered LASGLVamide, LFRFamide, LFRYamide, LRNFVamide, luqin, lymnokinin, myomodulin (two genes), the newly discovered NKY, NPY, pedal peptide (three genes), PKYMDT, pleurin, PXFVamide, small cardioactive peptides, tachykinins (two genes) and WWamide (an allatostatin B homolog). One gene was found to encode FWISamide, while about 20 closely related genes were found to encode WWFamide. These small neuropeptides appear homologous to the NdWFamide, which contains d-Trp; these genes are similar to the Aplysia gene encoding NWFamide. Some of these peptides had not been previously identified from mollusks, such as the predicted hormones similar to Drosophila and vertebrate insulins, bursicon, the putative proctolin homolog PKYMDT and allatostatin C. Together with neuropeptides which are likely homologs of other insect neuropeptides, such as cerebrin and WWamide, this shows that despite significant differences the molluscan and arthropod neuropeptidomes are more similar than generally recognized.

Stem cell therapy to treat diabetes mellitus

Transplantation of pancreatic islets offers a direct treatment for type 1 diabetes and in some cases, insulin-dependent type 2 diabetes. However, its widespread use is hampered by a shortage of donor organs. Many extant studies have focused on deriving beta-cell progenitors from pancreas and pluripotent stem cells. Efforts to generate beta-cells in vitro will help elucidate the mechanisms of beta-cell formation and thus provide a versatile in vivo system to evaluate the therapeutic potential of these cells to treat diabetes. Various successful experiments using beta-cells in animal models have generated extensive interest in using human embryonic stem cells to restore normoglycemia in diabetic patients. While new techniques are continually unveiled, the success of beta-cell generation rests upon successful manipulation of culture conditions and the induction of key regulatory genes implicated in pancreas development. In this review, we compare successfully conducted protocols, highlight essential steps and identify some of the remarkable shortfalls common to these methods. In addition, we discuss recent advancements in the derivation of patient-specific pluripotent stem cells that may facilitate the use of autologous beta-cells in stem cell therapy.