Identification, expression and bioactivity of a chitotriosidase-like homolog in amphioxus: Dependence of enzymatic and antifungal activities on the chitin-binding domain

Functional characterization of growth hormone releasing hormone and its receptor in amphioxus with implication for origin of hypothalamic-pituitary axis

Growth hormone-releasing hormone (GHRH) has been widely shown to stimulate growth hormone (GH) production via binding to GHRH receptor GHRHR in various species of vertebrates, but information regarding the functional roles of GHRH and GHRHR in the protochordate amphioxus remains rather scarce. We showed here that two mature peptides, BjGHRH-1 and BjGHRH-2, encoded by BjGHRH precursor, and a single BjGHRHR protein were identified in the amphioxus Branchiostoma. japonicum. Like the distribution profiles of vertebrate GHRHs and GHRHRs, both the genes Bjghrh and Bjghrhr were widely expressed in the different tissues of amphioxus, including in the cerebral vesicle, Hatschek's pit, neural tube, gill, hepatic caecum, notochord, testis and ovary. Moreover, both BjGHRH-1 and BjGHRH-2 interacted with BjGHRHR, and triggered the cAMP/PKA signal pathway in a dose-dependent manner. Importantly, BjGHRH-1 and BjGHRH-2 were both able to activate the expression of GH-like gene in the cells of Hatschek's pit. These indicate that a functional vertebrate-like GHRH-GHRHR axis had already emerged in amphioxus, which is a seminal innovation making physiological divergence including reproduction, growth, metabolism, stress and osmoregulation possible during the early evolution of vertebrates.

RNA interference-mediated silencing of ctl13 inhibits innate immunity and development in stored pest Tribolium castaneum

C-type lectins (CTLs) play a pivotal role in the regulation of insect immunity and growth, making them potential molecular targets for RNA interference (RNAi)-mediated pest control. Although multiple CTLs have been identified in the genomes of various insects, their specific functions and underlying molecular mechanisms remain unclear. In the present study, a novel CTL, Tcctl13 with a single CRD, was identified in Tribolium castaneum. Tcctl13 is expressed in diverse immune-related tissues and developmental stages, with a notable increase in its expression upon exposure to lipopolysaccharides (LPS) and peptidoglycan (PGN). Molecular docking and enzyme-linked immunosorbent assay (ELISA) analyses revealed that TcCTL13 possesses the ability interacted with LPS and PGN. The binding and agglutinating activities of recombinant TcCTL13 (rTcCTL13) were demonstrated against both gram-negative and positive bacteria. After using RNAi to silence Tcctl13, the expression of the eight antimicrobial peptide (AMP) genes was significantly reduced. In addition, knocking down Tcctl13 during the early larval or pupal stage hindered, the normal metamorphosis process in T. castaneum, ultimately leading to the demise of all beetles. Further research showed that Tcctl13 and nine AMPs were significantly downregulation after 20-Hydroxyecdysone (20E) injection. Instead, the up-regulation of Tcctl13 and six AMPs was observed following interference with the 20E receptor (ecdysone receptor, EcR), indicating that the function of Tcctl13 is regulated by 20E in T. castaneum. Collectively, these findings suggest that Tcctl13 plays a role in the regulation of innate immunity and development in T. castaneum, offering a promising molecular target for managing insect pests using RNAi-based approaches.

Activities of Family 18 Chitinases on Amorphous Regenerated Chitin Thin Films and Dissolved Chitin Oligosaccharides: Comparison with Family 19 Chitinases

Changes in mass and viscoelasticity of chitin layers in fungal cell walls during chitinase attack are vital for understanding bacterial invasion of and human defense against fungi. In this work, regenerated chitin (RChitin) thin films mimicked the fungal chitin layers and facilitated studies of degradation by family 18 chitinases from Trichoderma viride (T. viride) and family 19 chitinases from Streptomyces griseus (S. griseus) that possessed chitin-binding domains (CBDs) that were absent in the family 18 chitinases. Degradation was monitored via a quartz crystal microbalance with dissipation monitoring (QCM-D) in real time at various pH and temperatures. Compared to substrates of colloidal chitin or dissolved chitin derivatives and analogues, the degradation of RChitin films was deeply affected by chitinase adsorption. While the family 18 chitinases had greater solution activity on chitin oligosaccharides, the family 19 chitinases exhibited greater surface activity on RChitin films, illustrating the importance of CBDs for insoluble substrates.

Hepatic cecum: a key integrator of immunity in amphioxus

The vertebrate liver is regarded as an organ essential to the regulation of immunity and inflammation as well as being central to the metabolism of nutrients. Here, we discuss the functions that the hepatic cecum of amphioxus plays in the regulation of immunity and inflammation, and the molecular basis of this. It is apparent that the hepatic cecum performs important roles in the immunity of amphioxus including immune surveillance, clearance of pathogens and acute phase response. Therefore, the hepatic cecum, like the vertebrate liver, is an organ functioning as a key integrator of immunity in amphioxus.

Planarians (Platyhelminthes)-An Emerging Model Organism for Investigating Innate Immune Mechanisms

An organism responds to the invading pathogens such as bacteria, viruses, protozoans, and fungi by engaging innate and adaptive immune system, which functions by activating various signal transduction pathways. As invertebrate organisms (such as sponges, worms, cnidarians, molluscs, crustaceans, insects, and echinoderms) are devoid of an adaptive immune system, and their defense mechanisms solely rely on innate immune system components. Investigating the immune response in such organisms helps to elucidate the immune mechanisms that vertebrates have inherited or evolved from invertebrates. Planarians are non-parasitic invertebrates from the phylum Platyhelminthes and are being investigated for several decades for understanding the whole-body regeneration process. However, recent findings have emerged planarians as a useful model for studying innate immunity as they are resistant to a broad spectrum of bacteria. This review intends to highlight the research findings on various antimicrobial resistance genes, signaling pathways involved in innate immune recognition, immune-related memory and immune cells in planarian flatworms.

Linking Antimicrobial Potential of Natural Products Derived from Aquatic Organisms and Microbes Involved in Alzheimer's Disease - A Review

The following review is oriented towards microbes linked to Alzheimer's disease (AD) and antimicrobial effect of compounds and extracts derived from aquatic organisms against specific bacteria, fungi and viruses which were found previously in patients suffering from AD. Major group of microbes linked to AD include bacteria: Chlamydia pneumoniae, Helicobacter pylori, Porphyromonas gingivalis, Fusobacterium nucleatum, Prevotella intermedia, Actinomyces naeslundii, spirochete group; fungi: Candida sp., Cryptococcus sp., Saccharomyces sp., Malassezia sp., Botrytis sp., and viruses: herpes simplex virus type 1 (HSV-1), Human cytomegalovirus (CMV), hepatitis C virus (HCV). In the light of that fact, this review is the first to link antimicrobial potential of aquatic organisms against these sorts of microbes. This literature review might serve as a starting platform to develop novel supportive therapy for patients suffering from AD and to possibly prevent escalation of the disease in patients already having high-risk factors for AD occurrence.

Molecular characterization and expression analysis of chemokine (CXCL12) from Nile tilapia (Oreochromis niloticus)

Chemokines are a class of small molecular weight cytokines of 6-14 kDa, exerting important roles in the regulation of various inflammatory diseases and immune cell migration. In this study, we have identified the CXCL12 gene from Nile tilapia (Oreochromis niloticus), including CXCL12a (OnCXCL12a) and CXCL12b (OnCXCL12b). The open reading frames of OnCXCL12a and OnCXCL12b are 309 and 297 bp, encoding 102 and 98 amino acids, respectively. Multiple alignment showed that OnCXCL12a and OnCXCL12b have characteristics of CXC chemokines and share high identity with CXCL12 amino acid sequences from the known species. Tissue distribution in the healthy fish indicated that OnCXCL12a and OnCXCL12b expressed in all examined tissues, with the highest expression in muscle and anterior kidney, respectively. After challenged by Streptococcus agalactiae, Poly(I:C) and LPS in vivo and in vitro, OnCXCL12 is transcriptionally up-regulated in immune tissues and cells significantly. The recombinant OnCXCL12 proteins, (r)OnCXCL12a and (r)OnCXCL12b, enhance the release of nitric oxide and increase the expression of inflammatory cytokines (TNF-α, IL-6, and IL-10) in anterior kidney leukocytes, as well as exhibit chemotactic activity for leukocytes from anterior kidney. Summarizing, these results indicate that OnCXCL12 is involved in the immune response of Nile tilapia against pathogen infection and may play an important role in mediating inflammatory response.

Molecular and functional characterization of IL-6 receptor (IL-6R) and glycoprotein 130 (gp130) in Nile tilapia (Oreochromis niloticus)

Interleukin 6 (IL-6) is a pleiotropic cytokine that exerts its biological functions through interaction with its receptor system consisting of a ligand-specific IL-6 receptor (IL-6R) and a common signal-transducing receptor (gp130). In this study, OnIL-6R and Ongp130 genes from Nile tilapia (Oreochromis niloticus) were identified, and their roles in bacterial or viral infection and in regulation of inflammatory response involved in IL-6 were investigated. The open reading frames (ORFs) of OnIL-6R and Ongp130 are 2019 bp and 2679 bp, encoding 672 and 892 amino acids, respectively. Domain analysis of the deduced amino acid sequences of OnIL-6R and Ongp130 showed that both of them contained a conserved Ig-like domain, FNIII domains, and a WSXWS motif. The transcripts of OnIL-6R and Ongp130 were widely expressed in all examined tissues. Following in vivo challenges with Streptococcus agalactia, Poly I: C and lipopolysaccharide (LPS), the mRNAs of OnIL-6R and Ongp130 were notably induced in liver, head kidney and spleen. The transcriptional up-regulations of OnIL-6R and Ongp130 were also detected in Nile tilapia monocytes/macrophages and lymphocytes after in vitro stimulations with S. agalactiae, Poly I: C and LPS. Besides, increasing mRNA levels of the inflammation-related cytokines (IL-1β, TNF-α, IL-6, IL-10, and MIF) induced by recombinant OnIL-6 could be further enhanced by co-treatment with recombinant soluble OnIL-6R in lymphocytes. Furthermore, recombinant soluble Ongp130 suppressed the induction of expression of these cytokines in lymphocytes when co-stimulated with (r)OnIL-6 and (r)sOnIL-6R. Taken together, these results indicated that OnIL-6R and Ongp130 were likely involved in the resistance to bacterial or viral infection in Nile tilapia. Moreover, soluble OnIL-6R and soluble Ongp130 have an agonistic effect or antagonistic effect in the inflammation response involved in OnIL-6.

A novel hepatic lectin of zebrafish Danio rerio is involved in innate immune defense

ASGPR (asialoglycoprotein receptor, also known as hepatic lectin) was the first identified animal lectin, which participated in a variety of physiological processes. Yet its detailed immune functions are not well studied in lower vertebrates. After reporting a zebrafish hepatic lectin (Zhl), we identified a novel hepatic lectin (zebrafish hepatic lectin-like, Zhl-l) in zebrafish. The zhl-l was mainly expressed in liver in a tissue specific manner. And challenge with LPS/LTA induced a significant change of zhl-l expression. What's more, recombinant C-type lectin domain (rCTLD) of Zhl-l had the activity of agglutinating and binding to both Gram-negative and Gram-positive bacteria. It promoted the phagocytosis of bacteria by carp macrophages. Moreover, rCTLD could bind to insoluble lipopolysaccharide (LPS), lipoteichoic acid (LTA) and peptidoglycan (PGN) independent of Ca²⁺, which was inhibited by galactose. Interestingly, Zhl-l was located in the membrane, and its overexpression could upregulate the production of pre-inflammatory cytokines. Taken together, these results indicated that Zhl-l played a role in immune defense, and would provide further information to understand functions of C-type lectin family and the innate immunity in vertebrates.

Functional Characterization of Thyrostimulin in Amphioxus Suggests an Ancestral Origin of the TH Signaling Pathway

Thyrostimulin, consisting of GpA2 and GpB5 subunits, has been identified in amphioxus, but to date, little is known about the roles of GPA2/GPB5‒type hormone in this evolutionarily important animal. We showed here that amphioxus GpA2, GpB5, and TSH receptor (TSHR) represent the archetypes of vertebrate TSHα, TSHβ, and TSHR, respectively, and both gpa2 and gpb5 were coexpressed in the Hatschek pit, a homolog of the vertebrate pituitary, in amphioxus. We also showed that recombinant amphioxus GpA2 and GpB5, like zebrafish TSHα and TSHβ, bound to both amphioxus and zebrafish TSHR and that tethered amphioxus thyrostimulin activated both protein kinase A and protein kinase C pathways in the cells expressing amphioxus TSHR. Moreover, we demonstrated that recombinant amphioxus thyrostimulin induced the production of thyroid hormone (TH) T4. Because genuine TSH is absent in amphioxus and thyrostimulin is the only and sole glycoprotein hormone, our data likely provide evidence that amphioxus thyrostimulin is a functional glycoprotein hormone that plays a role as TSH does in vertebrates. The data also suggest that the TH signaling pathway evolved in the basal chordate more than 500 million years ago.

Chitin, chitinases, and chitin lectins: Emerging roles in human pathophysiology

Chitin is a simple β-linked repeating sugar polymer prominent in the building block structures of a wide variety of organisms, from the yeast cell wall to the exoskeleton and shells of arthropods and other forms of invertebrate life. It had previously been assumed that vertebrates did not contain chitins. However, chitin and chitinases are now documented to occur in vertebrate tissues. Chitin, chitinases and particularly chitinase-like proteins are involved in important human pathologies, though the mechanisms by which these function is unknown. These chitinase-like proteins bind to chitin and function as chitin lectins in that they bind to chitin but have lost the ability to degrade it. Emphasis is placed on one of the chitinase-like proteins, CHI3L1, that has acquired wide clinical importance. The purpose of this review is to place an array of bewildering observations associated with various human disorders into a framework, particularly the pathologies of the human gastro-intestinal tract. A reasonably cohesive story may eventually emerge.

Molecular Cloning of the Vitellogenin Gene and the Effects of Vitellogenin Protein Expression on the Physiology of Harmonia axyridis (Coleoptera: Coccinellidae)

Vitellogenin (Vg), the main egg storage protein precursor, plays an integral role in many oviparous animals, including Harmonia axyridis, an important agent for the biological control of many insect pests. In this study, the full-length Vg gene of was cloned. The open reading frame (ORF) of H. axyridis Vg cDNA is 5,403 bp in length and encodes 1,800 amino acids, with a predicted molecular mass of 211.88 KDa (accession number in NCBI: KX442718). Recombinant protein (18 kDa) expressed by the cloned Vg gene was characterized, and the effects of the expression of this protein on the physiology of H. axyridis were investigated. We found that Vg fragment significantly increased the egg production of H. axyridis. Furthermore, we also found that the activities of trypsin and lipase in H. axyridis were significantly higher in the groups treated with Vg fragment compared with those of the controls. The data from this study also reveals that Vg expression has significant effects on the physiology of H. axyridis and leads to increased egg production in these insects. These results may have future implications for increasing the reproduction rates of beneficial insects.

Functional characterization of avidins in amphioxus Branchiostoma japonicum: Evidence for a dual role in biotin-binding and immune response

Avidin is well known for its high affinity to biotin and has been found in many egg-laying vertebrate species. However, little is known about avidin in invertebrate species to date. Here we clearly showed the presence of two avidin genes, Bjavidin1 and Bjavidin2, in the amphioxus Branchiostoma japonicum, the first ones in non-vertebrate animals. We also showed that the expression of both Bjavidin1 and Bjavidin2 were inducible by progesterone, LTA and LPS. Moreover, we demonstrated for the first time that in addition to biotin-binding, the recombinant proteins rBjAVIDIN1 and rBjAVIDIN2 were not only able to interact with Gram-positive and negative bacteria as well as their conserved surface components LTA and LPS but also to enhance phagocytosis of bacteria by macrophages, suggesting that BjAVIDIN1 and BjAVIDIN2 both function as pattern recognition receptors and opsonins. It is thus clear that avidin may play a dual role in biotin-binding and immune response.

Functional characterization of Vitellogenin_N domain, domain of unknown function 1943, and von Willebrand factor type D domain in vitellogenin of the non-bilaterian coral Euphyllia ancora: Implications for emergence of immune activity of vitellogenin in basal metazoan

Our understanding of the function of vitellogenin (Vg) in reproduction has undergone a transformation over the past decade in parallel with new insights into the role of Vg in immunity. However, the time when Vg was endowed with immunological activities during animal evolution remains elusive. Here we demonstrate for the first time that the recombinant proteins rVitellogenin_N, rDUF1943, and rVWD from Vg of the basal metazoan coral Euphyllia ancora not only interact with Gram-positive and negative bacteria as well as their conserved surface components LTA and LPS but also enhance phagocytosis of bacteria by macrophages. Moreover, challenge with LPS results in a marked up-regulation of vg in the coral E. ancora. These data suggest that E. ancora Vg, like that described in the bilaterian oviparous animals fish and amphioxus, is a molecule related to antibacterial defense, indicating that the timing of the emergence of immune role of Vg predates the divergence of the cnidarian (non-bilaterian) and bilaterian lineages.

Identification and functional characterization of viperin of amphioxus Branchiostoma japonicum: Implications for ancient origin of viperin-mediated antiviral response

Viperin, an antiviral protein, has been shown to be active against a wide range of DNA and RNA viruses, but no information is available regarding functional characterization of viperin in invertebrate species. In this study, we clearly demonstrate that amphioxus (Branchiostoma japonicum) viperin, BjVip, has features in common with those of vertebrate viperin, including the presence of the SAM superfamily domain with the characteristic CNYKCGFC motif, syntenic conservation, and predicted 3D structure. Bjvip exhibits a tissue-specific expression with abundant levels in the hepatic cecum, hind-gut, gill and muscle, and following challenge with the viral mimic poly I:C, its expression is significantly up-regulated, suggesting an involvement of BjVip in immune response of amphioxus against viral infection. Importantly, we show that the cells transfected with Bjvip is able to kill LCDV or inhibiting its propagation, and co-incubation of rBjVip with WSSV markedly attenuates its infectivity. Thus, we provide the first evidences that amphioxus viperin, like that of vertebrates, is capable of promoting resistance against viral infection in vitro and in vivo, indicating that viperin-mediated antiviral response already emerged in the primitive chordate. We also prove that amphioxus viperin has evolved under positive selection.

Evolutionary conservation of molecular structure and antiviral function of a viral receptor, LGP2, in amphioxus Branchiostoma japonicum

RIG-I-like (where RIG-I is retinoic acid inducible gene I) receptor LGP2 (where LGP2 is laboratory of genetics and physiology) is an important intracellular receptor that recognizes viral RNAs in innate immunity, but its origin and evolution remains unknown. Here we clearly demonstrate the presence of a RIG-I-like receptor, BjLGP2, in the basal chordate amphioxus. It is predominantly expressed in the hepatic caecum and hindgut, and is upregulated following challenge with poly(I:C). BjLGP2 is distributed in the cytoplasm of both grouper spleen and flounder gill (FG) cells, and the recombinant BjLGP2 interacts with poly(I:C). BjLGP2 can enhance the expression of IFN and IFN-inducible genes in FG cells upon poly(I:C) challenge. It also significantly induces the expression of the antiviral genes ifn-i and Mx as well as the signal transduction relevant genes MAVS, NF-κB, and IRF-3 in FG cells upon lymphocystis disease virus challenge. Moreover, BjLGP2 inhibits the replication of lymphocystis disease virus in FG cells and the gene transcription of Singapore grouper iridovirus in grouper spleen cells. This is the first report showing that a LGP2 protein in invertebrate species (amphioxus) is structurally conserved and plays an antiviral role similar to that of vertebrate LGP2 proteins.

A manganese superoxide dismutase (MnSOD) from ark shell, Scapharca broughtonii: Molecular characterization, expression and immune activity analysis

Manganese superoxide dismutase (MnSOD) is one of the key members of the antioxidant defense enzyme family, however, data regarding to the immune function of MnSOD in mollusks still remain limited now. In this study, a full-length MnSOD cDNA was identified by rapid amplification of cDNA ends (RACE) method from cDNA library of ark shell Scapharca broughtonii (termed SbMnSOD). The cDNA contained an open reading frame (ORF) of 696 bp which encoded a polypeptide of 232 amino acids, a 5'-UTR with length of 32 bp and a 3'-UTR of 275 bp. Four putative amino acid residues (His-57, His-105, Asp-190 and His-194) responsible for manganese coordination were located in the most highly conserved regions of SbMnSOD and the signature sequence (DVWEHAYY) also existed in SbMnSOD. The deduced amino acid sequence of SbMnSOD shared high homology to MnSOD from other species. All those data revealed that the SbMnSOD was a novel member of the MnSOD family. The mRNA expression profiles of SbMnSOD in tissues of foot, gill, mantle, adductor muscle, hemocytes and hepatopancreas analyzed by quantitative real-time PCR (qRT-PCR) suggested the mRNA transcripts of SbMnSOD distributed in all the examined tissues. Importantly, Vibrio anguillarum challenge resulted in the increased expression of SbMnSOD mRNA with a regular change trend in all examined tissues, indicating SbMnSOD actively participated in the immune response process. What's more, further analysis on the antibacterial activity of the recombinant SbMnSOD showed that the fusion protein could remarkably inhibit growth of both Gram-positive and Gram-negative bacteria. The present results clearly suggested that SbMnSOD was an acute phase protein involved in the immune reaction in S. broughtonii.

Molecular cloning, expression, purification and characterization of vitellogenin in scallop Patinopecten yessoensis with special emphasis on its antibacterial activity

Vitellogenin (Vg), the major precursor of the egg-yolk proteins, has been found to play an immune role in fish and protochordate amphioxus, however, no study on the immune function of Vg in invertebrates has ever been studied before. In this study, the complete cDNA of Vg was identified from the scallop Patinopecten yessoensis (termed PyVg). The cDNA contained an open reading frame (ORF) of 6888 bp, encoding a polypeptide of 2295 amino acid protein, which had an N-terminal signal peptide followed by the mature Vg. The mature Vg had the domains Vitellogenin_N, domain of unknown function 1943 (DUF1943) and von Willebrand factor type D domain (VWD) as well as the consensus cleavage site (R-X-R/K-R) and conserved motif (KTIGNAG). Tissue distribution assay revealed that PyVg transcripts were predominantly present in the ovary and hepatopancreas, and its expression profile in ovary well reflected the annual cycle of vitellogenesis. Interestingly, bacterial challenge caused a significant change in PyVg expression, hinting an involvement of PyVg in the acute phase response in P. yessoensis. Consistently, recombinant DUF1943 and VWD domains both could interact with LTA and LPS on bacterial wall, and purified native PyVg displayed a broad-spectrum antibacterial activity against both Gram-negative (Escherichia coli and Vibrio anguillarum) and Gram-positive bacteria (Staphylococcus aureus). Overall, these data indicate that Vg is a pattern recognition molecule with bacterial growth-inhibiting activity in the scallop.

Functional characterization of chitinase-3 reveals involvement of chitinases in early embryo immunity in zebrafish

The function and mechanism of chitinases in early embryonic development remain largely unknown. We show here that recombinant chitinase-3 (rChi3) is able to hydrolyze the artificial chitin substrate, 4-methylumbelliferyl-β-D-N,N',N″-triacetylchitotrioside, and to bind to and inhibit the growth of the fungus Candida albicans, implicating that Chi3 plays a dual function in innate immunity and chitin-bearing food digestion in zebrafish. This is further corroborated by the expression profile of Chi3 in the liver and gut, which are both immune- and digestion-relevant organs. Compared with rChi3, rChi3-CD lacking CBD still retains partial capacity to bind to C. albicans, but its enzymatic and antifungal activities are significantly reduced. By contrast, rChi3-E140N with the putative catalytic residue E140 mutated shows little affinity to chitin, and its enzymatic and antifungal activities are nearly completely lost. These suggest that both enzymatic and antifungal activities of Chi3 are dependent on the presence of CBD and E140. We also clearly demonstrate that in zebrafish, both the embryo extract and the developing embryo display antifungal activity against C. albicans, and all the findings point to chitinase-3 (Chi3) being a newly-identified factor involved in the antifungal activity. Taken together, a dual function in both innate immunity and food digestion in embryo is proposed for zebrafish Chi3. It also provides a new angle to understand the immune role of chitinases in early embryonic development of animals.

Three in one: Identification, expression and enzymatic activity of lysozymes in amphioxus

The lysozymes identified so far in animals belong to the g-type, c-type, and i-type. Vertebrate animals possess only the former two types, i.e., g- and c-types, while all the three types have been reported in invertebrates. Here we demonstrate that (1) three cDNAs that encode g-, c-, and i-type lysozymes, respectively, were identified in a single species of the amphioxus Branchiostoma japonicum; (2) all the 3-type genes displayed distinct tissue-specific expression pattern; (3) recombinant g-, c-, and i-type lysozymes all exhibited enzymatic activities; and (4) native g-, c-, and i-type lysozymes were identified in the different tissues of amphioxus. Collectively, these results suggest the presence of all the 3-type lysozymes in a single animal species, first such data ever reported. The presence of biologically active i-type lysozyme in amphioxus also suggests that i-type lysozyme gene is retained at least in Protochordata, contrasting to the previous proposal that i-type lysozyme gene has been lost in a common ancestor of all chordates.

Structural and functional characterization of a TGFβ molecule from amphioxus reveals an ancient origin of both immune-enhancing and -inhibitory functions

Transforming growth factor beta (TGFβ) is a pleiotropic cytokine with important roles in mediating inflammatory response. TGFβ has been shown to be widely present in invertebrates, but little is known about its functions in immune and inflammatory responses. Moreover, structural and functional insights into TGFβ molecules in invertebrates remain completely lacking. Here we demonstrate the presence of a single TGFβ-like gene in the amphioxus Branchiostoma japonicum, Bjtgfβ, which represents the archetype of vertebrate TGFβ proteins, and displays a higher expression in the hind-gut, hepatic caecum, ovary, and gill. We also show that amphioxus TGFβ exerts both enhancing and suppressing effects on the migration of macrophages like RAW264.7, and the motif WSTD is important for TGFβ in inducing or inhibiting the migration of macrophages. Altogether, these data suggest that amphioxus TGFβ is phylogenetically and functionally similar to vertebrate TGFβ, suggesting an ancient origin of bipolar function of TGFβ proteins.

Initial symbiont contact orchestrates host-organ-wide transcriptional changes that prime tissue colonization

Upon transit to colonization sites, bacteria often experience critical priming that prepares them for subsequent, specific interactions with the host; however, the underlying mechanisms are poorly described. During initiation of the symbiosis between the bacterium Vibrio fischeri and its squid host, which can be observed directly and in real time, approximately five V. fischeri cells aggregate along the mucociliary membranes of a superficial epithelium prior to entering host tissues. Here, we show that these few early host-associated symbionts specifically induce robust changes in host gene expression that are critical to subsequent colonization steps. This exquisitely sensitive response to the host's specific symbiotic partner includes the upregulation of a host endochitinase, whose activity hydrolyzes polymeric chitin in the mucus into chitobiose, thereby priming the symbiont and also producing a chemoattractant gradient that promotes V. fischeri migration into host tissues. Thus, the host responds transcriptionally upon initial symbiont contact, which facilitates subsequent colonization.

Antifungal and antiviral products of marine organisms

Marine organisms including bacteria, fungi, algae, sponges, echinoderms, mollusks, and cephalochordates produce a variety of products with antifungal activity including bacterial chitinases, lipopeptides, and lactones; fungal (-)-sclerotiorin and peptaibols, purpurides B and C, berkedrimane B and purpuride; algal gambieric acids A and B, phlorotannins; 3,5-dibromo-2-(3,5-dibromo-2-methoxyphenoxy)phenol, spongistatin 1, eurysterols A and B, nortetillapyrone, bromotyrosine alkaloids, bis-indole alkaloid, ageloxime B and (-)-ageloxime D, haliscosamine, hamigeran G, hippolachnin A from sponges; echinoderm triterpene glycosides and alkene sulfates; molluscan kahalalide F and a 1485-Da peptide with a sequence SRSELIVHQR; and cepalochordate chitotriosidase and a 5026.9-Da antifungal peptide. The antiviral compounds from marine organisms include bacterial polysaccharide and furan-2-yl acetate; fungal macrolide, purpurester A, purpurquinone B, isoindolone derivatives, alterporriol Q, tetrahydroaltersolanol C and asperterrestide A, algal diterpenes, xylogalactofucan, alginic acid, glycolipid sulfoquinovosyldiacylglycerol, sulfated polysaccharide p-KG03, meroditerpenoids, methyl ester derivative of vatomaric acid, lectins, polysaccharides, tannins, cnidarian zoanthoxanthin alkaloids, norditerpenoid and capilloquinol; crustacean antilipopolysaccharide factors, molluscan hemocyanin; echinoderm triterpenoid glycosides; tunicate didemnin B, tamandarins A and B and; tilapia hepcidin 1-5 (TH 1-5), seabream SauMx1, SauMx2, and SauMx3, and orange-spotted grouper β-defensin. Although the mechanisms of antifungal and antiviral activities of only some of the aforementioned compounds have been elucidated, the possibility to use those known to have distinctly different mechanisms, good bioavailability, and minimal toxicity in combination therapy remains to be investigated. It is also worthwhile to test the marine antimicrobials for possible synergism with existing drugs. The prospects of employing them in clinical practice are promising in view of the wealth of these compounds from marine organisms. The compounds may also be used in agriculture and the food industry.

Functional analysis of domain of unknown function (DUF) 1943, DUF1944 and von Willebrand factor type D domain (VWD) in vitellogenin2 in zebrafish

Vitellogenin (Vg), the precursor of egg-yolk proteins in all oviparous organisms, shares a similar domain structure combination. In most cases, Vg contains the Vitellogenin_N domain, the domain of unknown function (DUF) 1943, and the von Willebrand factor type D domain (VWD), which are present in different forms of Vg from both vertebrates and invertebrates. Occasionally, a DUF1944 domain is also present in between DUF1943 and VWD in some Vg proteins of vertebrates. Recent studies have shown that Vg participates in immune defense of host with multiple functions. However, whether all Vg proteins encoded by different vg genes play an immune role is unknown. In addition, the correlation of different domains in Vg with the multiple immune functions remains completely unclear. Here we demonstrated clearly that recombinant proteins, rDUF1943, rDUF1944 and rVWD from zebrafish Vg2 interacted with both the Gram-positive bacteria Staphylococcus aureus, Bacillus subtilis and Micrococcus luteus and the Gram-negative bacteria Escherichia coli and Vibrio anguillarum, as well as their signature components LTA and LPS. Moreover, both rDUF1943 and rDUF1944 promoted the phagocytosis of E. coli and S. aureus by carp macrophages. These suggest that both DUF1943 and DUF1944 as well as VWD may contribute to the function of Vg as a pattern recognition receptor, and DUF1943 and DUF1944 also contribute to the function of Vg as an opsonin. This study also opens a new angle for identification of function of genes of unknown function, which have the domains DUF1943 and DUF1944.

Mucosal immunity in the gut: the non-vertebrate perspective

Much is now known about the vertebrate mechanisms involved in mucosal immunity, and the requirement of commensal microbiota at mucosal surfaces for the proper functioning of the immune system. In comparison, very little is known about the mechanisms of immunity at the barrier epithelia of non-vertebrate organisms. The purpose of this review is to summarize key experimental evidence illustrating how non-vertebrate immune mechanisms at barrier epithelia compare to those of higher vertebrates, using the gut as a model organ. Not only effector mechanisms of gut immunity are similar between vertebrates and non-vertebrates, but it also seems that the proper functioning of non-vertebrate gut defense mechanisms requires the presence of a resident microbiota. As more information becomes available, it will be possible to obtain a more accurate picture of how mucosal immunity has evolved, and how it adapts to the organisms' life styles.

Expression and functional analysis of properdin in zebrafish Danio rerio

Properdin, an upregulator of the alternative complement pathway, has been thoroughly studied in the mammalian species, but its research in the lower vertebrates such as fish is rather limited. Additionally, information regarding the structure-activity relationship of properdin remains rather fragmentary. In this report, we showed that zebrafish properdin gene zfp was abundantly expressed in the liver of adult fish, while it was primarily expressed in the brain, neural plate, developing lens, and neutrophil in the early embryos/larvae. Recombinant TSR modules of zfP were demonstrated to be able to bind to C3b, LPS, LTA and both gram-negative and positive bacteria. Moreover, TSR5 of zfP was able to enhance the phagocytosis of microbes by macrophages. These results together support the notion that properdin is a pattern recognition molecule capable of identifying non-self antigens/structures, and indicate that TSR5 plays a central role in the capacity of properdin to promote phagocytosis. It is also suggested that properdin is associated with the pattern formation and immune defense of early developing embryos/larvae.

Anti-viral activity of galectin-1 from flounder Paralichthys olivaceus

Galectins are a family of Ca(2+)-independent soluble lectins characterized by their affinity to β-galactosides. Mammalian galectins have been shown to play a defense role against certain bacteria, fungi and viruses. However, the immunological functions of galectins in fish is poorly characterized. Here we demonstrated that the expression of galectin-1 gene from the flounder Paralichthys olivaceus was decreased in the initial 8 h after challenge with poly I:C, then increased markedly from 24 h onwards, and the recombinant galectin-1 was able to neutralize the lymphocystis disease virus (LCDV), inhibiting the formation of cytopathic effects. In addition, the recombinant galectin had a potential anti-inflammatory activity against infection by LCDV, and was able to restrain the overexpression of the anti-viral protein gene mx against virus infection. These results indicate that flounder galectin-1 has an anti-viral activity, capable of reducing LCDV pathogenicity.