Involvement of sapecin in embryonic cell proliferation of Sarcophaga peregrina (flesh fly)

Identification of a novel strong promoter from the anhydrobiotic midge, Polypedilum vanderplanki, with conserved function in various insect cell lines

Larvae of the African midge Polypedilum vanderplanki (Diptera: Chironomidae) show a form of extreme desiccation tolerance known as anhydrobiosis. The cell line Pv11 was recently established from the species, and these cells can also survive under desiccated conditions, and proliferate normally after rehydration. Here we report the identification of a new promoter, 121, which has strong constitutive transcriptional activity in Pv11 cells and promotes effective expression of exogenous genes. Using a luciferase reporter assay, this strong transcriptional activity was shown to be conserved in cell lines from various insect species, including S2 (Drosophila melanogaster, Diptera), SaPe-4 (Sarcophaga peregrina, Diptera), Sf9 (Spodoptera frugiperda, Lepidoptera) and Tc81 (Tribolium castaneum, Coleoptera) cells. In conjunction with an appropriate selection maker gene, the 121 promoter was able to confer zeocin resistance on SaPe-4 cells and allowed the establishment of stable SaPe-4 cell lines expressing the fluorescent protein AcGFP1; this is the first report of heterologous gene expression in this cell line. These results show the 121 promoter to be a versatile tool for exogenous gene expression in a wide range of insect cell lines, particularly useful to those from non-model insect species.

Eggshell spheres protect brown widow spider ( Latrodectus geometricus) eggs from bacterial infection

Eggs provide a rich source of nutrients for the developing embryo, making them a favoured food source for other organisms as well. Several defence mechanisms have evolved to protect the developing embryos against microbial threats. In this article, we elucidate the defence strategy of brown widow spider ( Latrodectus geometricus) eggs against bacteria. Antibacterial activity was shown by inhibition of bacterial growth on agar plate, liquid culture and retarded biofilm formation. The defence strategy against bacterial invasion was demonstrated in the whole egg, whole egg extract, egg surface extract, eggshell and eggshell extract. The source and characteristics of this antibacterial activity are distinctive and stem in part from a dense layer of spheres covering the egg surface, likely originated from the oviposition fluid. The spheres are rich in low-molecular-weight proteins, yet their exact composition remains unknown. In this study, we demonstrate that the egg surface is hydrophobic, while the spheres are superhydrophilic. Egg surface roughness and hydrophobicity combined with its antibacterial chemical properties reduce the ability of bacteria to grow on the egg surface. Understanding the properties of these unique structures may contribute significantly to our knowledge of how nature deals with bacterial infections.

cDNA cloning and molecular characterization of a defensin-like antimicrobial peptide from larvae of Protaetia brevitarsis seulensis (Kolbe)

We identified new defensin-like cDNA (called Psdefensin) by searching data set of high-throughput RNA sequencing (RNA-seq) expression profiling of immunized larva of white-spotted flower chafers, Protaetia brevitarsis seulensis. The length of the analyzed new defensin-like sequences were 240 base pair (bp) and encoded the deduced polypeptide of 79 amino acid residues with signal peptides (amino acids 1-20), pro-peptide region (amino acids 21-36), and mature peptide region (amino acids 37-79). The Psdefensin transcript levels were slightly up-regulated at 4 h post-infection and were highly expressed at 8 h post-infection compared to control larvae injected with sterile water. In addition, the Psdefensin did have antimicrobial activity against both Gram-negative bacteria, E. coli and Gram-positive bacteria, B. subtilis suggesting potentially pharmacologic agent.

Cardiolipin Interactions with Proteins

Cardiolipins (CL) represent unique phospholipids of bacteria and eukaryotic mitochondria with four acyl chains and two phosphate groups that have been implicated in numerous functions from energy metabolism to apoptosis. Many proteins are known to interact with CL, and several cocrystal structures of protein-CL complexes exist. In this work, we describe the collection of the first systematic and, to the best of our knowledge, the comprehensive gold standard data set of all known CL-binding proteins. There are 62 proteins in this data set, 21 of which have nonredundant crystal structures with bound CL molecules available. Using binding patch analysis of amino acid frequencies, secondary structures and loop supersecondary structures considering phosphate and acyl chain binding regions together and separately, we gained a detailed understanding of the general structural and dynamic features involved in CL binding to proteins. Exhaustive docking of CL to all known structures of proteins experimentally shown to interact with CL demonstrated the validity of the docking approach, and provides a rich source of information for experimentalists who may wish to validate predictions.

Insect antimicrobial peptides and their applications

Insects are one of the major sources of antimicrobial peptides/proteins (AMPs). Since observation of antimicrobial activity in the hemolymph of pupae from the giant silk moths Samia Cynthia and Hyalophora cecropia in 1974 and purification of first insect AMP (cecropin) from H. cecropia pupae in 1980, over 150 insect AMPs have been purified or identified. Most insect AMPs are small and cationic, and they show activities against bacteria and/or fungi, as well as some parasites and viruses. Insect AMPs can be classified into four families based on their structures or unique sequences: the α-helical peptides (cecropin and moricin), cysteine-rich peptides (insect defensin and drosomycin), proline-rich peptides (apidaecin, drosocin, and lebocin), and glycine-rich peptides/proteins (attacin and gloverin). Among insect AMPs, defensins, cecropins, proline-rich peptides, and attacins are common, while gloverins and moricins have been identified only in Lepidoptera. Most active AMPs are small peptides of 20-50 residues, which are generated from larger inactive precursor proteins or pro-proteins, but gloverins (~14 kDa) and attacins (~20 kDa) are large antimicrobial proteins. In this mini-review, we will discuss current knowledge and recent progress in several classes of insect AMPs, including insect defensins, cecropins, attacins, lebocins and other proline-rich peptides, gloverins, and moricins, with a focus on structural-functional relationships and their potential applications.

Fly immunity: recognition of pathogens and induction of immune responses

Despite the lack of adaptive immunity based on gene rearrangement such as that in higher vertebrates, flies are able to defend themselves from a wide array of pathogens using multiple innate immune responses whose molecular mechanisms are strikingly similar to those of the innate immune responses of other multicellular organisms, including humans. Invading pathogens passing through the epithelial barriers, the first line of self-defense, are detected by pattern recognition receptors that identify pathogen-associated molecular patterns in the hemolymph or on the immune cell surface and are eliminated by humoral and cellular responses. Some pathogens escape recognition and elimination in the hemolymphby invading the host cell cytoplasm. Some of these intracellular pathogens, however, such as Listeria monocytogenes, are identified by pattern recognition receptors in the cytoplasm and are eliminated by intracellular responses, including autophagy, an intracellular degradation system. Although some of these pattern recognition receptors are encoded in the germ-line as protein families, another type of receptor in the immunoglobulin-superfamily is extensively diversified by alternative splicing in somatic immune cells in Drosophila.

Molecules participating in insect immunity of Sarcophaga peregrina

Pricking the body wall of Sarcophaga peregrina (flesh fly) larvae with a needle activated the immune system of this insect and induced various immune molecules, including antibacterial proteins, in the hemolymph. In this review, I summarize and discuss the functions of these immune molecules, with particular emphasis on the dual roles of some of these molecules in defense and development.

The malaria vector mosquito Anopheles gambiae expresses a suite of larval-specific defensin genes

cDNAs of Anopheles gambiae Defensin 2 (AgDef2), Defensin 3 (AgDef3) and Defensin 4 (AgDef4), identified in the genome sequence, have been characterized and their expression profiles investigated. In contrast to both typical defensins and insect antimicrobial peptides generally, the newly identified defensins were not upregulated with acute-phase kinetics following immune challenge in insects or cell culture. However, mRNA abundance of AgDef2, AgDef3 and AgDef4 increased significantly during the larval stages. Promoter analysis of all three genes failed to identify putative immune response elements previously identified in other mosquito defensin genes. As previous studies failed to identify these larval-specific defensins, it seems likely that further antimicrobial peptide genes with nontypical expression profiles will be identified as more genome sequences become available.

Function of antimicrobial proteins in insects

We have isolated and characterized various antimicrobial proteins from the haemolymph of Sarcophaga peregrina (flesh fly) larvae. Of these the sarcotoxin I family is a group of proteins mainly active against Gram-negative bacteria whereas sapecin is active mainly against Gram-positive bacteria. In addition to its function in defence, sapecin also plays a role in insect development. Recently, we identified a hendecapeptide of the sapecin homologue sapecin B that has the same antibacterial activity as the original sapecin B. Both sarcotoxin I and sapecin are inducible proteins synthesized de novo by the fat body and/or haemocytes and secreted into the haemolymph when the insect is in the acute phase response to bacterial infection. Antifungal protein (AFP) is constitutively present in the haemolymph and is active against certain fungi but not bacteria. These various antimicrobial proteins interact with microbial membranes. Sarcotoxin I interferes with membrane functions such as ATP synthesis and amino acid transport. The fungicidal activity of AFP is enhanced synergistically by sarcotoxin I, although sarcotoxin I alone has no appreciable antifungal activity. It is clear that the flesh fly has the ability to mount a potent defence response against microbial parasites by mobilizing several antimicrobial proteins.

Recognition and elimination of diversified pathogens in insect defense systems

The elimination of infectious non-self by the host defense systems of multicellular organisms requires a variety of recognition and effector molecules. The diversity is generated in somatic cells or encoded in the germ-line. In adaptive immunity in jawed vertebrates, the diversity of immunoglobulins and antigen receptors is generated by gene rearrangements in somatic cells. In innate immunity, various effector molecules and pattern recognition receptors, such as antimicrobial peptides and peptidoglycan recognition proteins, are encoded in the germ-line of multicellular organisms, including insects and jawed vertebrates. In the present review, we discuss how insect host defense systems recognize and eliminate a multitude of microbes via germ-line-encoded molecules, including recent findings that a Drosophila member of the immunoglobulin superfamily is extensively diversified by alternative splicing in somatic immune cells and participates in the elimination of bacteria.

Long-term maintenance of in vitro cultured honeybee (Apis mellifera) embryonic cells

BACKGROUND

In vitro cultivation of cells allows novel investigation of in vivo- mechanisms and is a helpful tool in developmental biology, biochemistry and functional genomics. Numerous cell lines of insect species, e.g., silkworm and mosquito, have been reported. However, this is not the case for successful long-term cultivation of cells in honeybees.

RESULTS

Methods for cultivation of honeybee embryonic cells are discussed here. Pre-gastrula stage embryos were used to initiate cultures, and cells were reared on 96-wells microplates with Grace insect medium, supplemented with Fetal Bovine Serum. Cells proliferated in clusters, and maintained viable and mitotic for more than three months.

CONCLUSION

We report here, for the first time, long-term cultivation of honeybee cells. Results represent a highly useful in vitro-system for studying a model organism of increasing importance in areas such as aging, sociality and neurobiology.

Bacterial challenge stimulates innate immune responses in extra-embryonic tissues of tobacco hornworm eggs

Innate immunity protects juvenile and adult vertebrates and invertebrates against potential pathogens; however, it is unknown when developing embryos become immune competent and just how they are guarded from infection. To address these questions, we studied the effect of immune challenge on early stage eggs of the tobacco hornworm, Manduca sexta. We detected many immune-related proteins and mRNAs in naive eggs. Upon immune challenge, antimicrobial protein genes were up-regulated, and antibacterial activity increased. Antimicrobial protein mRNAs and lysozyme were present in the extra-embryonic tissues of immune-challenged eggs; in addition, melanization in response to bacteria occurred in the yolk but not embryonic tissues. We conclude that the extra-embryonic tissues of early stage M. sexta eggs are immune competent and likely protect the developing embryo from infection. We suggest that innate immune responses of extra-embryonic tissues may be a common mechanism for protecting early embryos.

Antibacterial peptide defensin is involved in midgut immunity of the soft tick, Ornithodoros moubata

Two defensin genes A and B were previously demonstrated to be up-regulated by blood feeding in the soft tick, Ornithodoros moubata [Nakajima et al. (2001) Two isoforms of a member of the arthropod defensin family from the soft tick, Ornithodoros moubata (Acari: Argasidae). Insect Biochem Mol Biol 31: 747-751]. In this study, two defensin isoforms C and D similar to defensins A and B were newly cloned. A total of four defensins have been identified in O. moubata. All four Ornithodoros defensins are coded as prepro-defensins. Ornithodoros defensin genes consist of four exons and three introns, an organization reported in mussel defensins but not insect defensins. Ornithodoros defensin C and D genes are predominantly expressed in the midgut and up-regulated in response to blood feeding. The mature peptide of the previously cloned Ornithodoros defensin A was purified from the midgut lumen, indicating defensin is secreted into the midgut. These findings confirm the involvement of Ornithodoros defensin in midgut immunity.

Exploration of mosquito immunity using cells in culture

The propagation of immune-responsive cells in vitro has provided the basis for substantial contributions to our understanding of many aspects of the mammalian immune response. In contrast, the potential for exploring the innate immune response of insects using cultured cells is only beginning to be developed, particularly with various mosquito cell lines from the genera Aedes and Anopheles. Immune-reactive mosquito cell lines express various defensive factors, including transferrin, lysozyme, cecropin, defensin, and prophenoloxidase activities. In this review, we discuss insect immunity in the context of key concepts that have emerged in the study of the mammalian immune system, with emphasis on the properties of the cells that participate in the immune response. The nature of established cell lines and their contributions to our understanding of immune functions in humans and insects is described, with emphasis on our own work with the C7-10 and Aag-2 mosquito cell lines from Aedes albopictus and Aedes aegypti, respectively. Finally, we offer some speculation on further advances in insect immunology that may be facilitated by work with cells in culture.

Male-specific IDGF, a novel gene encoding a membrane-bound extracellular signaling molecule expressed exclusively in testis of Drosophila melanogaster

We identified a novel gene of Drosophila melanogaster, Male-specific IDGF (MSI), encoding a transmembrane signaling molecule with exclusive expression in the testis. This molecule (MSI) contains a single transmembrane domain and has 35% amino acid identity with insect-derived growth factor (IDGF), a soluble growth factor for embryonic cells of the flesh fly, Sarcophaga peregrina. When MSI was exogenously expressed in Schneiders's line 2 cells, it was shown to be localized on the cell surface and exhibits growth factor activity, suggesting that MSI is a membrane-bound extracellular signaling molecule. Gene expression studies revealed that MSI mRNA was restricted to mature primary spermatocytes, whereas MSI was detected in the cells at the later developmental stages. Analysis using four meiotic arrest mutants, aly, can, mia, and sa suggested that MSI is involved in spermiogenesis, the final differentiation step of spermatogenesis. These results suggest that MSI is an extracellular signaling molecule participating in spermatogenesis and is a new member of the IDGF family.

The roles of Sarcophaga defense molecules in immunity and metamorphosis

This article summarizes recent progress (1996 1998) in our studies on self-defense molecules in Sarcophaga peregrina. A new antibacterial substance was purified and its unique structure and function revealed a novel aspect of the Sarcophaga defense system. We found a novel lectin and cysteine protease in hemocytes which will assist in the understanding of immune response of hemocytes. There have been two major advances in research on the regulation of defense gene induction: (i) cDNA cloning of a new transcriptional factor binding to the kappaB-like promoter sequence of the Sarcophaga lectin gene, (ii) methylation of cytosolic factors essential for induction of immune genes in the fatbody. Metamorphosis is an interesting event from an immunological point of view: (i) a novel protease with antibacterial activity was discovered from metamorphosing gut, and (ii) a pupal hemocyte-specific surface antigen was purified and characterized in terms of its structure and possible function for larval tissue recognition and elimination.

Regeneration of Sarcophaga imaginal discs in vitro: implication of 20-hydroxyecdysone

When the 3/4 sectors of leg imaginal discs of Sarcophaga were cultured in vitro in the presence of 2.5 x 10(-8) M 20-hydroxyecdysone, wound healing and restoration of their morphology occurred. This concentration of ecdysone was critical for wound healing and was 40 times lower than that necessary for inducing differentiation of imaginal discs in vitro. Lost positional values revealed by expression of the wingless gene were found to show partial recovery under these conditions. These results suggest that a low titer of ecdysone is essential for the regeneration of imaginal discs.

Purification, characterization, and cDNA cloning of a novel growth factor from the conditioned medium of NIH-Sape-4, an embryonic cell line of Sarcophaga peregrina (flesh fly)

A growth factor from the conditioned medium of NIH-Sape-4, an embryonic cell line of the flesh fly, was purified to homogeneity. This growth factor, termed IDGF, stimulated the proliferation of NIH-Sape-4 cells in an autocrine manner; it was a homodimer of a protein with a molecular mass of 52 kDa, and its specific activity was comparable with those of mammalian growth factors. Immunoblotting experiments revealed that unfertilized mature eggs of the flesh fly contained this growth factor, a certain level of which was maintained throughout embryonic development. Analysis of cDNA for this growth factor showed that this factor is a novel protein consisting of 553 amino acid residues. No significant sequence similarity was found between this factor and other proteins except atrial gland granule-specific antigen of Aplysia californica.

Inhibition of the Ca(2+)-activated K(+)-channel by sapecin B, an insect antibacterial protein

Sapecin is an antibacterial protein of the flesh fly and sapecin B is its homologue structurally similar to charybdotoxin of scorpion venom, which is known to be a K+ channel inhibitor. We found that, like charybdotoxin, sapecin B inhibits part of the voltage pulse-induced K+ currents of rat cerebellar Purkinje cells. We suggest that this effect is due to inhibition of the Ca(+)-activated K+ channel. Probably, sapecin B is a naturally occurring K+ channel inhibitor as well as an antibacterial protein.

The inducible antibacterial peptides of insects

Insects respond to bacterial challenge by the rapid and transient synthesis of a large number of potent antibacterial peptides that are active against many different bacteria. Two families of inducible antibacterial peptides are well characterized: the cecropins and the insect defensins. A rapidly increasing number of proline- and glycine-rich peptides are reported from various insect species together with cecropins and insect defensins. In this review, Stéphane Cociancich, Philippe Bulet, Charles Hetru and Jules A. Hoffmann give an update of our current information on the induced antibacterial peptides.

Synthesis of charybdotoxin and of two N-terminal truncated analogues. Structural and functional characterisation

Charybdotoxin and two N-terminal truncated peptides, corresponding to the 2-37 and 7-37 sequences, were obtained by stepwise solid-phase synthesis using N alpha-t-butyloxycarbonyl and benzyltype side-chain protection. While this strategy was generally useful, the S-acetamidomethyl protecting group used for the six cysteines was not completely stable under HF treatment and its subsequent removal by mercury(II) treatment was neither complete nor devoid of side reactions. The completely deprotected native and truncated sequences were folded efficiently in the presence of glutathione and were finally purified by high-pressure liquid chromatography with overall yields of 4.0-5.0%. Each protein was characterised chemically, structurally and functionally. 1H-NMR spectroscopy was used and a complete assignment of all the protons of the three synthetic proteins was achieved. NMR data show that synthetic charybdotoxin is indistinguishable from the natural protein. The two truncated proteins contain the same elements of secondary structure and a similar overall three-dimensional structure, in agreement with circular dichroic measurements. The shortest analogue, however, may have local structural perturbations and/or higher flexibility. Biological activity on dog epithelial Ca(2+)-activated K+ channels and on rat brain synaptosomal voltage-dependent K+ channels show that synthetic charybdotoxin was as potent as the natural toxin on both channels. For both channels, deletion of the first amino acid, 5-oxoproline (pyroglutamic acid) decreased only slightly the potency of the inhibitor, while deletion of the entire 1-6 segment reduced potency much more. We conclude that the N-terminal region of charybdotoxin plays a functional role in tuning the toxin's biological activity but is not essential for the folding and stability of the structure. The structure of the shortest analogue represents an interesting example of how a well organised and stable alpha/beta fold can be engineered with only 31 amino acid residues.

Purification, sequence and antibacterial activity of two novel sapecin homologues from Sarcophaga embryonic cells: similarity of sapecin B to charybdotoxin

Two sapecin homologues were purified from the culture medium of NIH-Sape-4, an embryonic cell line of Sarcophaga peregrina (flesh fly). These homologues contained six cysteine residues with exactly the same disulphide pairings as those in sapecin. The amino acid sequence of one of them, sapecin C, was also very similar to that of sapecin. The other homologue, sapecin B, was less similar to sapecin but showed significant similarity to charybdotoxin, an inhibitor of K+ channels isolated from a scorpion venom. Like sapecin, these homologues repressed the growth of various Gram-positive bacteria.

The fate of the prosegment in the acute-phase and programmed synthesis of sapecin, an antibacterial peptide of the flesh fly (Sarcophaga peregrina)

The nucleotide sequence of sapecin cDNA suggested that this antibacterial peptide of the flesh fly (Sarcophaga peregrina) is produced from preprosapecin by post-translational processing. We examined the production of sapecin and its prosegment by radioimmunoassay under two different physiological conditions in which its gene is activated, assuming that the prosegment has some biological role. Results suggested that the prosegment is degraded selectively during production of sapecin. We also found that imaginal discs synthesize sapecin when cultured in the presence of 20-hydroxyecdysone.

Insect defensins: inducible antibacterial peptides

In response to bacterial challenge or trauma, insects produce a battery of bactericidal or bacteriostatic molecules with a broad spectrum of activity against Gram-positive and/or Gram-negative bacteria; most are small-sized cationic peptides. This review focuses on insect defensins, a large group of inducible antibacterial peptides that are present both in ancient and recent insect orders. This immune response of insects shares many of the characteristics of the mammalian acute phase response.

Progress in multidimensional NMR investigations of peptide and protein 3-D structures in solution. From structure to functional aspects

2-D and 3-D NMR techniques were used to investigate the conformations in solution of several peptides and proteins for which crystalline structures are not available yet. Insect defensin A is a small (40 aa) antibiotic protein exhibiting a characteristic 'loop-helix-beta-sheet' structure. A striking analogy was found with charybdotoxin, a scorpion toxin in which a CSH (cysteine stabilized alpha-helix) motif is also present. Wheat phospholipid transfer protein (PLTP) (90 aa) has a 3-D structure resulting from the packing of four helices and of a C-terminal less well-defined fragment. Preliminary results show that PLTP forms a complex with lyso-PC and that such an interaction results in a conformational change affecting principally the C-terminal half of the protein. A last example is given with surfactin, a lipopeptide biosurfactant from bacterial origin. Its protonated form shows a very compact structure in which the two acidic residues located on the top of a 'horse saddle' topology face each other, whereas the ionized form could adopt a more extended conformation. A common property of these compounds is their capacity to interact with lipids. The present structural data open the way for a further establishment of structure-activity relationships.