Expression of PACAP-like compounds during the caudal regeneration of the earthworm Eisenia fetida

Same same, but different: exploring the enigmatic role of the pituitary adenylate cyclase-activating polypeptide (PACAP) in invertebrate physiology

Evidence has been accumulating that elements of the vertebrate pituitary adenylate cyclase-activating polypeptide (PACAP) system are missing in non-chordate genomes, which is at odds with the partial sequence-, immunohistochemical-, and physiological data in the literature. Multilevel experiments were performed on the great pond snail (Lymnaea stagnalis) to explore the role of PACAP in invertebrates. Screening of neuronal transcriptome and genome data did not reveal homologs to the elements of vertebrate PACAP system. Despite this, immunohistochemical investigations with an anti-human PAC1 receptor antibody yielded a positive signal in the neuronal elements in the heart. Although Western blotting of proteins extracted from the nervous system found a relevant band for PACAP-38, immunoprecipitation and mass spectrometric analyses revealed no corresponding peptide fragments. Similarly to the effects reported in vertebrates, PACAP-38 significantly increased cAMP synthesis in the heart and had a positive ionotropic effect on heart preparations. Moreover, it significantly modulated the effects of serotonin and acetylcholine. Homologs to members of Cluster B receptors, which have shared common evolutionary origin with the vertebrate PACAP receptors, PTHRs, and GCGRs, were identified and shown not to be expressed in the heart, which does not support a potential role in the mediation of PACAP-induced effects. Our findings support the notion that the PACAP system emerged after the protostome-deuterostome divergence. Using antibodies against vertebrate proteins is again highlighted to have little/no value in invertebrate studies. The physiological effects of vertebrate PACAP peptides in protostomes, no matter how similar they are to those in vertebrates, should be considered non-specific.

Terahertz pulses induce segment renewal via cell proliferation and differentiation overriding the endogenous regeneration program of the earthworm Eisenia andrei

Terahertz (THz) irradiation of excised Eisenia andrei earthworms is shown to cause overriding of the genetically determined, endogenously mediated segment renewing capacity of the model animal. Single-cycle THz pulses of 5 µJ energy, 0.30 THz mean frequency, 293 kV/cm peak electric field, and 1 kHz repetition rate stimulated the cell proliferation (indicated by the high number of mitotic cells) and both histogenesis and organogenesis, producing a significantly higher number of regenerated segments. The most conspicuous alteration in THz-treated animals was the more intense development of the new central nervous system and blood vessels. These results clearly demonstrate that THz pulses are capable to efficiently trigger biological processes and suggest potential applications in medicine.

Identification of a novel collagen-like peptide by high-throughput screening for effective wound-healing therapy

Tissue regeneration and wound healing are still serious clinical complications globally and lack satisfactory cures. Inspired by the impressive regeneration ability of the post-injury earthworms and their widely accepted medicinal properties, we screened and identified a novel collagen-like peptide from the amputated earthworms using high-throughput techniques, including transcriptomics, proteomics, and mass spectrum. The identified collagen-like peptide col4a1 was cloned and expressed to comprehensively investigate the wound healing effect and underlying mechanism. It exerted significant effects on wound healing both in vitro and in vivo, including enhanced viability, proliferation, migration of fibroblasts, granulation, and collagen deposition. Moreover, the col4a1 functioned via binding with integrin α₂β₁ and upregulating the RAS/MAPK signaling pathway. This work demonstrates that the novel collagen-like peptide col4a1 obtained from the amputated earthworms enables enhanced wound healing and provides new opportunities for wound care.

Injury-Induced Innate Immune Response During Segment Regeneration of the Earthworm, Eisenia andrei

Regeneration of body parts and their interaction with the immune response is a poorly understood aspect of earthworm biology. Consequently, we aimed to study the mechanisms of innate immunity during regeneration in Eisenia andrei earthworms. In the course of anterior and posterior regeneration, we documented the kinetical aspects of segment restoration by histochemistry. Cell proliferation peaked at two weeks and remitted by four weeks in regenerating earthworms. Apoptotic cells were present throughout the cell renewal period. Distinct immune cell (e.g., coelomocyte) subsets were accumulated in the newly-formed blastema in the close proximity of the apoptotic area. Regenerating earthworms have decreased pattern recognition receptors (PRRs) (e.g., TLR, except for scavenger receptor) and antimicrobial peptides (AMPs) (e.g., lysenin) mRNA patterns compared to intact earthworms. In contrast, at the protein level, mirroring regulation of lysenins became evident. Experimental coelomocyte depletion caused significantly impaired cell divisions and blastema formation during anterior and posterior regeneration. These obtained novel data allow us to gain insight into the intricate interactions of regeneration and invertebrate innate immunity.

Tracing the Origins of the Pituitary Adenylate-Cyclase Activating Polypeptide (PACAP)

Pituitary adenylate cyclase activating polypeptide (PACAP) is a well-conserved neuropeptide characteristic of vertebrates. This pluripotent hypothalamic neuropeptide regulates neurotransmitter release, intestinal motility, metabolism, cell division/differentiation, and immunity. In vertebrates, PACAP has a specific receptor (PAC₁) but it can also activate the Vasoactive Intestinal Peptide receptors (VPAC₁ and VPAC₂). The evolution of the vertebrate PACAP ligand - receptor pair has been well-described. In contrast, the situation in invertebrates is much less clear. The PACAP ligand - receptor pair in invertebrates has mainly been studied using heterologous antibodies raised against mammalian peptides. A few partial PACAP cDNA clones sharing >87% aa identity with vertebrate PACAP have been isolated from a cnidarian, several protostomes and tunicates but no gene has been reported. Moreover, current evolutionary models of the peptide and receptors using molecular data from phylogenetically distinct invertebrate species (mostly nematodes and arthropods) suggests the PACAP ligand and receptors are exclusive to vertebrate genomes. A basal deuterostome, the cephalochordate amphioxus (Branchiostoma floridae), is the only invertebrate in which elements of a PACAP-like system exists but the peptides and receptor share relatively low sequence conservation with the vertebrate homolog system and are a hybrid with the vertebrate glucagon system. In this study, the evolution of the PACAP system is revisited taking advantage of the burgeoning sequence data (genome and transcriptomes) available for invertebrates to uncover clues about when it first appeared. The results suggest that elements of the PACAP system are absent from protozoans, non-bilaterians, and protostomes and they only emerged after the protostome-deuterostome divergence. PACAP and its receptors appeared in vertebrate genomes and they probably shared a common ancestral origin with the cephalochordate PACAP/GCG-like system which after the genome tetraploidization events that preceded the vertebrate radiation generated the PACAP ligand and receptor pair and also the other members of the Secretin family peptides and their receptors.

PACAP deficiency as a model of aging

Dysregulation of neuropeptides may play an important role in aging-induced impairments. In the long list of neuropeptides, pituitary adenylate cyclase-activating polypeptide (PACAP) represents a highly effective cytoprotective peptide that provides an endogenous control against a variety of tissue-damaging stimuli. PACAP has neuro- and general cytoprotective effects due to anti-apoptotic, anti-inflammatory, and antioxidant actions. As PACAP is also a part of the endogenous protective machinery, it can be hypothesized that the decreased protective effects in lack of endogenous PACAP would accelerate age-related degeneration and PACAP knockout mice would display age-related degenerative signs earlier. Recent results support this hypothesis showing that PACAP deficiency mimics aspects of age-related pathophysiological changes including increased neuronal vulnerability and systemic degeneration accompanied by increased apoptosis, oxidative stress, and inflammation. Decrease in PACAP expression has been shown in different species from invertebrates to humans. PACAP-deficient mice display numerous pathological alterations mimicking early aging, such as retinal changes, corneal keratinization and blurring, and systemic amyloidosis. In the present review, we summarize these findings and propose that PACAP deficiency could be a good model of premature aging.

Large scale changes in the transcriptome of Eisenia fetida during regeneration

Earthworms show a wide spectrum of regenerative potential with certain species like Eisenia fetida capable of regenerating more than two-thirds of their body while other closely related species, such as Paranais litoralis seem to have lost this ability. Earthworms belong to the phylum Annelida, in which the genomes of the marine oligochaete Capitella telata and the freshwater leech Helobdella robusta have been sequenced and studied. Herein, we report the transcriptomic changes in Eisenia fetida (Indian isolate) during regeneration. Following injury, E. fetida regenerates the posterior segments in a time spanning several weeks. We analyzed gene expression changes both in the newly regenerating cells and in the adjacent tissue, at early (15days post amputation), intermediate (20days post amputation) and late (30 days post amputation) by RNAseq based de novo assembly and comparison of transcriptomes. We also generated a draft genome sequence of this terrestrial red worm using short reads and mate-pair reads. An in-depth analysis of the miRNome of the worm showed that many miRNA gene families have undergone extensive duplications. Sox4, a master regulator of TGF-beta mediated epithelial-mesenchymal transition was induced in the newly regenerated tissue. Genes for several proteins such as sialidases and neurotrophins were identified amongst the differentially expressed transcripts. The regeneration of the ventral nerve cord was also accompanied by the induction of nerve growth factor and neurofilament genes. We identified 315 novel differentially expressed transcripts in the transcriptome, that have no homolog in any other species. Surprisingly, 82% of these novel differentially expressed transcripts showed poor potential for coding proteins, suggesting that novel ncRNAs may play a critical role in regeneration of earthworm.

Environmental pollutants, pathogens and immune system in earthworms

Earthworms also known as farmer's friends are natural tillers of soil. They belong to Phylum Annelida and class Oligochaeta. Acid soils with organic matter and surface humus maintain the largest fauna of worms and earthworms. Due to their habitat in soil, they are constantly exposed to microbes and pollution generated by anthropogenic sources. Studies have revealed that damage of the immune system of earthworms can lead to alterations of both morphological and cellular characteristics of worms, activation of signalling pathways and can strongly influence their survival. Therefore, the understanding of the robust immune system in earthworms has become very important from the point of view of understanding its role in combating pathogens and pollutants and its role in indicating the soil pollution. In this article, we have outlined the (i) components of the immune system and (ii) their function of immunological responses on exposure to pollutants and pathogens. This study finds importance from the point of view of ecotoxicology and monitoring of earthworm health and exploring the scope of earthworm immune system components as biomarkers of pollutants and environmental toxicity. The future scope of this review remains in understanding the earthworm immunobiology and indicating strong biomarkers for pollution.

Presence and Effects of Pituitary Adenylate Cyclase Activating Polypeptide Under Physiological and Pathological Conditions in the Stomach

Pituitary adenylate cyclase activating polypeptide (PACAP) is a multifunctional neuropeptide with widespread occurrence throughout the body including the gastrointestinal system. In the small and large intestine, effects of PACAP on cell proliferation, secretion, motility, gut immunology and blood flow, as well as its importance in bowel inflammatory reactions and cancer development have been shown and reviewed earlier. However, no current review is available on the actions of PACAP in the stomach in spite of numerous data published on the gastric presence and actions of the peptide. Therefore, the aim of the present review is to summarize currently available data on the distribution and effects of PACAP in the stomach. We review data on the localization of PACAP and its receptors in the stomach wall of various mammalian and non-mammalian species, we then give an overview on PACAP's effects on secretion of gastric acid and various hormones. Effects on cell proliferation, differentiation, blood flow and gastric motility are also reviewed. Finally, we outline PACAP's involvement and changes in various human pathological conditions.

Investigation into the cellular origins of posterior regeneration in the annelid Capitella teleta

Many animals can regenerate, although there is great diversity in regenerative capabilities. A major question in regenerative biology is determining the cellular source of newly formed tissue. The polychaete annelid, Capitella teleta, can regenerate posterior segments following transverse amputation. However, the source, behavior and molecular characteristics of the cells that form new tissue during regeneration are largely unknown. Using an indirect cell tracking method involving 5′‐ethynyl‐2′‐deoxyuridine (EdU) incorporation, we show that cell migration occurs during C. teleta posterior regeneration. Expression of the multipotency/germ line marker CapI‐vasa led us to hypothesize that stem cells originate from a multipotent progenitor cell (MPC) cluster, migrate through the coelomic cavity, and contribute to regeneration of tissue. We show that the capacity for posterior regeneration and segment formation is greater with than without the MPC cluster. Finally, we propose a working model of posterior regeneration in C. teleta. This work is the first in C. teleta that addresses the potential source of cells contributing to posterior regeneration, and may provide clues as to why some animals are highly successful regenerators.

Annotation of nerve cord transcriptome in earthworm Eisenia fetida

In annelid worms, the nerve cord serves as a crucial organ to control the sensory and behavioral physiology. The inadequate genome resource of earthworms has prioritized the comprehensive analysis of their transcriptome dataset to monitor the genes express in the nerve cord and predict their role in the neurotransmission and sensory perception of the species. The present study focuses on identifying the potential transcripts and predicting their functional features by annotating the transcriptome dataset of nerve cord tissues prepared by Gong et al., 2010 from the earthworm Eisenia fetida. Totally 9762 transcripts were successfully annotated against the NCBI nr database using the BLASTX algorithm and among them 7680 transcripts were assigned to a total of 44,354 GO terms. The conserve domain analysis indicated the over representation of P-loop NTPase domain and calcium binding EF-hand domain. The COG functional annotation classified 5860 transcript sequences into 25 functional categories. Further, 4502 contig sequences were found to map with 124 KEGG pathways. The annotated contig dataset exhibited 22 crucial neuropeptides having considerable matches to the marine annelid Platynereis dumerilii, suggesting their possible role in neurotransmission and neuromodulation. In addition, 108 human stem cell marker homologs were identified including the crucial epigenetic regulators, transcriptional repressors and cell cycle regulators, which may contribute to the neuronal and segmental regeneration. The complete functional annotation of this nerve cord transcriptome can be further utilized to interpret genetic and molecular mechanisms associated with neuronal development, nervous system regeneration and nerve cord function.

A Stable Thoracic Hox Code and Epimorphosis Characterize Posterior Regeneration in Capitella teleta

Regeneration, the ability to replace lost tissues and body parts following traumatic injury, occurs widely throughout the animal tree of life. Regeneration occurs either by remodeling of pre-existing tissues, through addition of new cells by cell division, or a combination of both. We describe a staging system for posterior regeneration in the annelid, Capitella teleta, and use the C. teleta Hox gene code as markers of regional identity for regenerating tissue along the anterior-posterior axis. Following amputation of different posterior regions of the animal, a blastema forms and by two days, proliferating cells are detected by EdU incorporation, demonstrating that epimorphosis occurs during posterior regeneration of C. teleta. Neurites rapidly extend into the blastema, and gradually become organized into discrete nerves before new ganglia appear approximately seven days after amputation. In situ hybridization shows that seven of the ten Hox genes examined are expressed in the blastema, suggesting roles in patterning the newly forming tissue, although neither spatial nor temporal co-linearity was detected. We hypothesized that following amputation, Hox gene expression in pre-existing segments would be re-organized to scale, and the remaining fragment would express the complete suite of Hox genes. Surprisingly, most Hox genes display stable expression patterns in the ganglia of pre-existing tissue following amputation at multiple axial positions, indicating general stability of segmental identity. However, the three Hox genes, CapI-lox4, CapI-lox2 and CapI-Post2, each shift its anterior expression boundary by one segment, and each shift includes a subset of cells in the ganglia. This expression shift depends upon the axial position of the amputation. In C. teleta, thoracic segments exhibit stable positional identity with limited morphallaxis, in contrast with the extensive body remodeling that occurs during regeneration of some other annelids, planarians and acoel flatworms.

Immune system participates in brain regeneration and restoration of reproduction in the earthworm Dendrobaena veneta

Earthworm decerebration causes temporary inhibition of reproduction which is mediated by certain brain-derived neurohormones; thus, cocoon production is an apposite supravital marker of neurosecretory center functional recovery during brain regeneration. The core aim of the present study was to investigate aspects of the interactions of nervous and immune systems during brain regeneration in adult Dendrobaena veneta (Annelida; Oligochaeta). Surgical brain extirpation was combined, either with (i) maintenance of immune-competent coelomic cells (coelomocytes) achieved by surgery on prilocaine-anesthetized worms or (ii) prior extrusion of fluid-suspended coelomocytes by electrostimulation. Both brain renewal and cocoon output recovery were significantly faster in earthworms with relatively undisturbed coelomocyte counts compared with individuals where coelomocyte counts had been experimentally depleted. These observations provide empirical evidence that coelomocytes and/or coelomocyte-derived factors (e.g. riboflavin) participate in brain regeneration and, by implication, that there is close functional synergy between earthworm neural and immune systems.

First report of the pituitary adenylate cyclase activating polypeptide (PACAP) in crustaceans: conservation of its functions as growth promoting factor and immunomodulator in the white shrimp Litopenaeus vannamei

The high conservation of the pituitary adenylate cyclase activating polypeptide (PACAP) sequence indicates that this peptide fulfills important biological functions in a broad spectrum of organisms. However, in invertebrates, little is known about its presence and its functions remain unclear. Up to now, in non-mammalian vertebrates, the majority of studies on PACAP have focused mainly on the localization, cloning and structural evolution of this peptide. As yet, little is known about its biological functions as growth factor and immunomodulator in lower vertebrates. Recently, we have shown that PACAP, apart from its neuroendocrine role, influences immune functions in larval and juvenile fish. In this work, we isolated for the first time the cDNA encoding the mature PACAP from a crustacean species, the white shrimp Litopenaeus vannamei, corroborating its high degree of sequence conservation, when compared to sequences reported from tunicates to mammalian vertebrates. Based on this, we have evaluated the effects of purified recombinant Clarias gariepinus PACAP administrated by immersion baths on white shrimp growth and immunity. We demonstrated that PACAP improves hemocyte count, superoxide dismutase, lectins and nitric oxide synthase derived metabolites in treated shrimp related with an increase in total protein concentration and growth performance. From our results, PACAP acts as a regulator of shrimp growth and immunity, suggesting that in crustaceans, as in vertebrate organisms, PACAP is an important molecule shared by both the endocrine and the immune systems.

Localization and characterization of sulfated glycosaminoglycans in the body of the earthworm Eisenia andrei (Oligochaeta, Annelida)

The aim of this study was to characterize the compartmental distribution of sulfated glycosaminoglycans (S-GAGs) in adults and their occurrence during the development of the earthworm Eisenia andrei. S-GAGs were extracted from the body of earthworms to identify their composition and the time of their appearance and disappearance in embryonic, newborn, juvenile, and adult earthworms. S-GAGs were also analyzed in earthworm tissue using histochemical metachromatic staining. Purified S-GAGs obtained from the whole body of adult earthworms were composed of chondroitin sulfate (CS) and heparan sulfate (HS). In addition, an unknown, highly sulfated polysaccharide (HSP) was detected. In order to characterize specifically the S-GAG composition in the integument, earthworms were dissected and as much as possible of their viscera was removed. HS and CS were the predominant sulfated polysaccharides in the dissected integument, whereas in viscera, CS, HS and the HSP were found in proportions similar to those identified in the body. The qualitative S-GAG composition in juveniles was similar to that obtained from adult earthworms. CS was the predominant S-GAG in newborn earthworms, accompanied by lesser amounts of HS and by tiny amounts of the HSP. This study provides a detailed descriptive account of the pattern of S-GAG synthesis during development, and also the characterization of the tissue distribution of these compounds in the body of earthworms.

Pituitary adenylate cyclase-activating polypeptide-like compounds could modulate the activity of coelomocytes in the earthworm

By means of radioimmunoassay, we studied the concentration of pituitary adenylate cyclase-activating polypeptide (PACAP)-like proteins in intact and regenerating earthworms. Transection of animals increased the concentration of PACAP-like compounds in coelomocytes, and a decreasing rostrocaudal gradient was detected in the regenerating animals. Western blot analysis revealed a range of PAC1-receptor proteins with molecular weights from 40 to 80 kDa. Electron microscopic immunocytochemistry showed that PAC1 receptors were located on distinct sets of coelomocytes (mainly on amebocytes and on some granulocytes). Based on our results we hypothesize a link between PACAP and coelomocytes, suggesting that PACAP modulates the function of amebocytes and certain granulocytes that play a role in tissue remodeling of regenerating earthworms.