Adjacent GATA and kappa B-like motifs regulate the expression of a Drosophila immune gene

BmNPV interacts with super-enhancer regions of the host chromatin to hijack cellular transcription machinery

Effective transcriptional activation relies on the spatial interaction between specific DNA elements. DNA interactions have also been observed between DNA viruses and their hosts, with limited understanding of the involved details. Baculovirus is a representative species of DNA virus and has been reported to interact with the host genome in our previous study. However, the biological significance of the baculovirus-host trans-species DNA interaction and its underlying mechanisms remain elusive. Here, using Bombyx mori nucleopolyhedrovirus (BmNPV) as the model virus, we combine epigenome, transcriptome, and biochemical assays to investigate the baculovirus-host DNA interaction. Our data show that BmNPV hijacks the transcriptional regulatory capacity of host super-enhancers (SEs) by physically interacting with these regions on the host genome. This results in the usurpation of the activating capacity of an SE-binding transcription factor GATA by the virus, thereby impairing the SE-induced specific transcriptional activation of the target antiviral genes. Moreover, the hijacked regulatory capacity is spread on BmNPV genome through cis-interaction of viral DNA, leading to enhanced viral gene expression. Overall, our results provide novel insights into the intricate interplay of viruses with host gene expression regulatory networks and broaden the vision in the mechanisms of viral exploitation on cellular machinery.

The Enhanced activation of innate immunity in Drosophila S2 cells by Micrococcus luteus VKM Ac-2230 is mediated by Relish

The canonical model of immune response activation in Drosophila suggests that the IMD pathway is activated by Gram-negative (Gram (-)) bacteria, while the Toll pathway is activated by both Gram-positive bacteria (Gram (+)) and fungi. However, the mechanisms by which these pathogens promote cross-activation of these pathways remain controversial. In addition, the mechanisms of cross-activation in S2 cell culture remain unstudied. In this study, we investigated the role of two Gram (+) bacteria (Micrococcus luteus and Bacillus subtilis) and fungal spores (Metarhizium anisopliae) in activating the IMD pathway in S2 cell cultures. Cells were treated with Escherichia coli as a control to ensure the specificity of IMD pathway activation. Our results demonstrated a significant involvement of M. luteus in the activation of the IMD pathway in S2 cell cultures. This is evidenced by the marked activation of IMD pathway-dependent genes, as well as the proteolytic cleavage of the Relish protein, which serves as a key transcription factor for this pathway. We also observed a strong recruitment of Relish to the promoters of antimicrobial peptide (AMP) genes, along with a partial recruitment to the genes encoding peptidoglycan recognition proteins (PGRPs). Furthermore, RNA interference targeting Relish resulted in a significant reduction in the transcription levels of all AMP genes and most PGRPs. Similarly, we analyzed the contributions of B. subtilis and M. anisopliae to the cross-activation of the IMD pathway. Our data indicate that both B. subtilis and M. anisopliae also activate the IMD pathway, albeit to a lesser extent compared to M. luteus. At the same time, fungal spores exhibited minimal influence on the activation of the IMD pathway when compared to Gram (+) bacteria. Thus, we have investigated in detail the mechanisms of cross-activation of the immune response in S2 cell culture, suggesting that Relish may play a critical role in inducing a humoral immune response in Drosophila S2 cells, primarily against M. luteus and to a lesser extent against B. subtilis and M. anisopliae.

The evolutionary novelty of insect defensins: from bacterial killing to toxin neutralization

Insect host defense comprises two complementary dimensions, microbial killing-mediated resistance and microbial toxin neutralization-mediated resilience, both jointly providing protection against pathogen infections. Insect defensins are a class of effectors of innate immunity primarily responsible for resistance to Gram-positive bacteria. Here, we report a newly originated gene from an ancestral defensin via genetic deletion following gene duplication in Drosophila virilis, which confers an enhanced resilience to Gram-positive bacterial infection. This gene encodes an 18-mer arginine-rich peptide (termed DvirARP) with differences from its parent gene in its pattern of expression, structure and function. DvirARP specifically expresses in D. virilis female adults with a constitutive manner. It adopts a novel fold with a 310 helix and a two CXC motif-containing loop stabilized by two disulfide bridges. DvirARP exhibits no activity on the majority of microorganisms tested and only a weak activity against two Gram-positive bacteria. DvirARP knockout flies are viable and have no obvious defect in reproductivity but they are more susceptible to the DvirARP-resistant Staphylococcus aureus infection than the wild type files, which can be attributable to its ability in neutralization of the S. aureus secreted toxins. Phylogenetic distribution analysis reveals that DvirARP is restrictedly present in the Drosophila subgenus, but independent deletion variations also occur in defensins from the Sophophora subgenus, in support of the evolvability of this class of immune effectors. Our work illustrates for the first time how a duplicate resistance-mediated gene evolves an ability to increase the resilience of a subset of Drosophila species against bacterial infection.

Tumor necrosis factor receptor-associated factor 6 (TRAF6) participates in anti-lipopolysaccharide factors (ALFs) gene expression in mud crab

Tumor necrosis factor receptor-associated factor 6 (TRAF6) is a key cytoplasm signal adaptor that mediates signals activated by tumor necrosis factor receptor (TNFR) superfamily and the Interleukin-1 receptor/Toll-like receptor (IL-1/TLR) superfamily. The full-length 2492 bp TRAF6 (Sp-TRAF6) from Scylla paramamosain contains 1800 bp of open reading frame (ORF) encoding 598 amino acids, including an N-terminal RING-type zinc finger, two TRAF-type zinc fingers and a conserved C-terminal meprin and TRAF homology (MATH) domain. Multiple alignment analysis shows that the putative amino acid sequence of Sp-TRAf6 has highest identity of 88% with Pt-TRAF6 from Portunus trituberculatus, while the similarity of Sp-TRAF6 with other crustacean sequences was 54-55%. RT-PCR analysis indicated that Sp-TRAF6 transcripts were predominantly expressed in the hepatopancreas and stomach, whereas it was barely detected in the heart and hemocytes in our study. Moreover, Sp-TRAF6 transcripts were significantly up-regulated after Vibrio parahemolyticus and LPS challenges. RNA interference assay was carried out used by siRNA to investigate the genes expression patterns regulated by Sp-TRAF6. The qRT-PCR results showed that silencing Sp-TRAF6 gene could inhibit SpALF1, SpALF2, SpALF5 and SpALF6 expression in hemocytes, while inhibit SpALF1, SpALF3, SpALF4, SpALF5 and SpALF6 expression in hepatopancreas. Taken together, the acute-phase response to immune challenges and the inhibition of SpALFs gene expression indicate that Sp-TRAF6 plays an important role in host defense against pathogen invasions via regulation of ALF gene expression in S. paramamosain.

In vivo activity and the transcriptional regulatory mechanism of the antimicrobial peptide SpHyastatin in Scylla paramamosain

A new gene homologous to the reported antimicrobial peptide (AMP) hyastatin from Hyas araneus was screened in the SSH library constructed from the hemocytes of Scylla paramamosain, and named SpHyastatin. In vivo study showed that SpHyastatin was predominantly expressed in hemocytes of S. paramamosain. With the challenge of either Vibrio parahaemolyticus or lipopolysaccharide (LPS), SpHyastatin showed a positive response, meaning that it was probably involved in the immune reaction against bacterial infection in vivo. A distinctive feature of SpHyastatin in comparison with six other known AMPs tested was that SpHyastatin could maintain a higher transcription level from megalopas to the adult crab, indicating a potential consistent resistance against pathogens conferred by this peptide existing in the blood circulation of crabs. RNA interference assay was performed to inhibit SpHyastatin transcription in vivo and the result demonstrated that silencing SpHyastatin mRNA transcripts could decrease the survival rate of crabs challenged with V. parahaemolyticus. To further understand the molecular mechanisms that regulate SpHyastatin expression, a 576 bp 5'-flanking sequence of SpHyastatin was obtained using genome walking. Here, we focused our experiments on investigating the roles of the putative NF-κB binding site in LPS-mediated transcriptional regulation of the SpHyastatin gene using endothelial progenitor cells and Hela cells. Luciferase reporter analyses demonstrated that the putative NF-κB element acted as a positive regulatory element and was essential for the induction of SpHyastatin promoter by LPS. These results should shed light on the in vivo functional property and the molecular mechanism of regulation for the crab AMP SpHyastatin.

Characterization of the Bombyx mori Cecropin A1 promoter regulated by IMD pathway

Cecropin A1 (CecA1) promoter from Bombyx mori was cloned and characterized to provide insight into the transcriptional control of this antimicrobial peptide gene upon immune challenges. Reporter gene assays demonstrated that both Escherichia coli and lipopolysaccharide could induce expression in BmE cells but B. bombyseptieus or peptidoglycan failed, and the induction pattern of the reporter gene was coincident with the endogenous CecA1. Analysis of deletion and mutation constructs revealed that the regulatory region was the κB motif located between -176 and -166, and no other predicted elements on CecA1 promoter affected its inducibility. Insertion of additional κB motifs increased the activity of CecA1 promoter. Furthermore, binding of Relish to κB motif was confirmed by electrophoretic mobility shift assay. These findings indicate the regulatory mechanism of CecA1 expression in IMD pathway and suggest an approach of engineering antimicrobial peptide promoter with enhanced activities that may lead to broad applications.

Viruses and antiviral immunity in Drosophila

Viral pathogens present many challenges to organisms, driving the evolution of a myriad of antiviral strategies to combat infections. A wide variety of viruses infect invertebrates, including both natural pathogens that are insect-restricted, and viruses that are transmitted to vertebrates. Studies using the powerful tools in the model organism Drosophila have expanded our understanding of antiviral defenses against diverse viruses. In this review, we will cover three major areas. First, we will describe the tools used to study viruses in Drosophila. Second, we will survey the major viruses that have been studied in Drosophila. And lastly, we will discuss the well-characterized mechanisms that are active against these diverse pathogens, focusing on non-RNAi mediated antiviral mechanisms. Antiviral RNAi is discussed in another paper in this issue.

The shrimp IKK-NF-κB signaling pathway regulates antimicrobial peptide expression and may be subverted by white spot syndrome virus to facilitate viral gene expression

The IκB kinases IKKα and IKKβ and the IKK-related kinases TANK-binding kinase 1 (TBK1) and IKKε are the master regulators of the NF-κB signaling pathway. Although this pathway has been extensively studied in mammals, less attention has been paid in crustaceans, which have significant economic value. Here, we report the cloning and functional studies of two IKK homologs, LvIKKβ and LvIKKε, from Pacific white shrimp, Litopenaeus vannamei. LvIKKβ and LvIKKε mRNAs are widely expressed in different tissues and are responsive to white spot syndrome virus (WSSV) infection. When overexpressed in Drosophila S2 cells, LvIKKβ but not LvIKKε activates the promoters of NF-κB pathway-controlled antimicrobial peptide genes (AMPs), such as the Penaeidins (PENs). In HEK 293T cells, both LvIKKβ and LvIKKε activate an NF-κB reporter. The silencing of LvIKKβ or LvIKKε using double-stranded RNA (dsRNA)-mediated RNA interference (RNAi) decreases the expression of L. vannamei AMPs, including PENs, lysozyme and crustins. Intriguingly, LvIKKβ- or LvIKKε-silenced L. vannamei are resistant to WSSV infection. We hypothesized that successful infection with WSSV requires the activation of the IKK–NF-κB signaling pathway to modulate viral gene expression. We constructed luciferase reporters for 147 WSSV genes. By screening, we found that the WSV051, WSV059, WSV069, WSV083, WSV090, WSV107, WSV244, WSV303, WSV371 and WSV445 promoters can be activated by LvIKKβ or LvIKKε in Drosophila S2 cells. Taken together, our results reveal that LvIKKβ and LvIKKε may participate in the regulation of shrimp AMPs and that WSSV may subvert the L. vannamei IKK–NF-κB signaling pathway to facilitate viral gene expression.

Ecdysone triggered PGRP-LC expression controls Drosophila innate immunity

Throughout the animal kingdom, steroid hormones have been implicated in the defense against microbial infection, but how these systemic signals control immunity is unclear. Here, we show that the steroid hormone ecdysone controls the expression of the pattern recognition receptor PGRP-LC in Drosophila, thereby tightly regulating innate immune recognition and defense against bacterial infection. We identify a group of steroid-regulated transcription factors as well as two GATA transcription factors that act as repressors and activators of the immune response and are required for the proper hormonal control of PGRP-LC expression. Together, our results demonstrate that Drosophila use complex mechanisms to modulate innate immune responses, and identify a transcriptional hierarchy that integrates steroid signalling and immunity in animals.

Nucleotide sequence and chromosomal localization of the gene for pierisin-1, a DNA ADP-ribosylating protein, in the cabbage butterfly Pieris rapae

Cabbage butterfly, Pieris rapae, contains a unique DNA ADP-ribosylating protein, pierisin-1, which transfers ADP-ribose moiety of NAD to guanine bases of DNA. Pierisin-like proteins are only distributed in subtribes Pierina, Aporiina and Appiadina of the family Pieridae. In this study, we obtained genomic clones carrying the pierisin-1 gene from adult samples of P. rapae by plaque hybridization. The pierisin-1 gene was found to consist of two exons, 0.1-kb exon 1 and 3.9-kb exon 2, and a 2.3-kb intron. In addition, we could demonstrate that the putative promoter in the about 3-kb upstream region from the transcription start site of the gene include a transcriptional activating motif involved in immune pathways and hormonal regulation. We also examined chromosomal localization of the pierisin-1 gene. Fluorescence in situ hybridization (FISH) analysis using Cy3-labeled pierisin-1 genomic clone demonstrated the localization of the gene near the kinetochore in chromosome 9. Thus, we confirmed that the pierisin-1 gene is located in the genome of P. rapae.

Immune response in the barrier epithelia: lessons from the fruit fly Drosophila melanogaster

The barrier epithelia of multicellular organisms frequently come into direct contact with microorganisms and thus need to fulfill the important task of preventing the penetration of pathogens that could cause systemic infections. A functional immune defence in the epithelial linings of the digestive, respiratory and reproductive organs as well as the epidermis/skin of animals is therefore of crucial importance for survival. Epithelial defence reactions are likely to be evolutionarily ancient, and the use of invertebrate animal models, such as insects and nematodes, has been crucial in unravelling the mechanisms underlying epithelial immunity. This review addresses basic questions of epithelial immunity in animals and humans. It focuses on recent developments in the understanding of the immune responses in the fruit fly Drosophila melanogaster and how the innate immune system acts locally in the epidermis and cuticle, tracheae, gut and genital organs. Both basal immune activities in epithelia that are constantly exposed to microbes as well as positive and negative regulation in response to pathogenic organisms are covered. Important immuno-physiological aspects of epithelial defence mechanisms are also discussed, such as wound healing, re-epithelialization and intestinal homeostasis.

Prolixicin: a novel antimicrobial peptide isolated from Rhodnius prolixus with differential activity against bacteria and Trypanosoma cruzi

We identified and characterized the activity of prolixicin, a novel antimicrobial peptide (AMP) isolated from the hemipteran insect, Rhodnius prolixus. Sequence analysis reveals one region of prolixicin that may be related to the diptericin/attacin family of AMPs. Prolixicin is an 11-kDa peptide containing a putative 21 amino acid signal peptide, two putative phosphorylation sites and no glycosylation sites. It is produced by both adult fat body and midgut tissues in response to bacterial infection of the haemolymph or the midgut. Unlike most insect antibacterial peptides, the prolixicin gene does not seem to be regulated by NF-κB binding sites, but its promoter region contains several GATA sites. Recombinant prolixicin has strong activity against the Gram-negative bacterium Escherichia coli and differential activity against several Gram-negative and Gram-positive bacteria. No significant toxicity was demonstrated against Trypanosoma cruzi, the human parasite transmitted by R. prolixus.

Manduca sexta moricin promoter elements can increase promoter activities of Drosophila melanogaster antimicrobial peptide genes

Insects produce a variety of antimicrobial peptides (AMPs). Induction of insect AMP genes is regulated by the Toll and IMD (immune deficiency) pathways via NF-κB and GATA factors. Little is known about species-specific regulation of AMP genes. In this report, we showed that activities of most Manduca sexta and Drosophila melanogaster AMP gene promoters were regulated in a species-specific manner in Drosophila (Dipteran) S2 cells and Spodoptera frugiperda (Lepidopteran) Sf9 cells. A κB-GATA element (22 bp) from M. sexta moricin (MsMoricin) promoter could significantly increase activities of Drosophila AMP gene promoters in S2 cells, and an MsMoricin promoter activating element (MPAE) (140 bp) could increase activity of drosomycin promoter specifically in Sf9 cells. However, κB and GATA factors alone were not sufficient for MsMoricin gene activation, suggesting that other co-regulators may be required to fully activate AMP genes. Our results suggest that induction of insect AMP genes may require a transcription complex composed of common nuclear factors (such as NF-κB and GATA factors) and species-related co-regulators, and it is the co-regulators that may confer species-specific regulation of AMP genes. In addition, we showed that activity of Drosophila drosomycin promoter could be activated cooperatively by the inserted exogenous κB-GATA element and the endogenous κB element. These findings revealed an approach of engineering AMP genes with enhanced activities, which may lead to broad applications.

Identification, phylogenetic analysis and expression profile of an anionic insect defensin gene, with antibacterial activity, from bacterial-challenged cotton leafworm, Spodoptera littoralis

Background

Defensins are a well known family of cationic antibacterial peptides (AMPs) isolated from fungi, plants, insects, mussels, birds, and various mammals. They are predominantly active against gram (+) bacteria, and a few of them are also active against gram (-) bacteria and fungi. All insect defensins belonging to the invertebrate class have a consensus motif, C-X_5-16-C-X₃-C-X_9-10-C-X_4-7-CX₁-C. Only seven AMPs have already been found in different lepidopteran species. No report was published on the isolation of defensin from the Egyptian cotton leafworm, Spodoptera littoralis.

Results

An anionic defensin, termed SpliDef, was isolated from the haemolymph of the cotton leafworm, S. littoralis, after bacterial challenge using differential display technique. Based on sequence analyses of the data, specific primers for full length and mature peptide of defensin were designed and successfully amplified 471 and 150 bp amplicons. The integration of the results revealed that the 471 bp-PCR product has one open reading frame (orf) of 303 bp long, including both start codon (AUG) and stop codon (UGA). The deduced peptide consists of a 23-residues signal peptide, a 27-residues propeptide and a 50-residues mature peptide with the conserved six-cysteine motif of insect defensins. Both haemolymph and expressed protein exhibited antibacterial activities comparable to positive control. The RT-qPCR indicated that it was more than 41-folds up-regulated at 48 h p.i.

Conclusion

Our results highlight an important immune role of the defensin gene in Spodoptera littoralis by cooperating with other AMPs to control bacterial infection.

Litopenaeus vannamei tumor necrosis factor receptor-associated factor 6 (TRAF6) responds to Vibrio alginolyticus and white spot syndrome virus (WSSV) infection and activates antimicrobial peptide genes

Tumor necrosis factor receptor (TNFR)-associated factor 6 (TRAF6) is a key signaling adaptor protein not only for the TNFR superfamily but also for the Interleukin-1 receptor/Toll-like receptor (IL-1/TLR) superfamily. To investigate TRAF6 function in invertebrate innate immune responses, Litopenaeus vannamei TRAF6 (LvTRAF6) was identified and characterized. The full-length cDNA of LvTRAF6 is 2823bp long, with an open reading frame (ORF) encoding a putative protein of 594 amino acids, including a RING-type Zinc finger, two TRAF-type Zinc fingers, a coiled-coil region, and a meprin and TRAF homology (MATH) domain. The overall amino acid sequence identity between LvTRAF6 and other known TRAF6s is 22.2-33.3%. Dual luciferase reporter assays in Drosophila S2 cells revealed that LvTRAF6 could activate the promoters of antimicrobial peptide genes (AMPs), including Drosophila Attacin A and Drosomycin, and shrimp Penaeidins. Real-time quantitative PCR (qPCR) indicated that LvTRAF6 was constitutively expressed in various tissues of L. vannamei. After Vibrio alginolyticus and white spot syndrome virus (WSSV) challenge, LvTRAF6 was down-regulated, though with different expression patterns in the intestine compared to other tissues. After WSSV challenge, LvTRAF6 was up-regulated 2.7- and 2.3-fold over the control at 3h in gills and hepatopancreas, respectively. These results indicated that LvTRAF6 may play a crucial role in antibacterial and antiviral responses via regulation of AMP gene expression.

NF-κB/Rel proteins and the humoral immune responses of Drosophila melanogaster

Nuclear Factor-κB (NF-κB)/Rel transcription factors form an integral part of innate immune defenses and are conserved throughout the animal kingdom. Studying the function, mechanism of activation and regulation of these factors is crucial for understanding host responses to microbial infections. The fruit fly Drosophila melanogaster has proved to be a valuable model system to study these evolutionarily conserved NF-κB mediated immune responses. Drosophila combats pathogens through humoral and cellular immune responses. These humoral responses are well characterized and are marked by the robust production of a battery of anti-microbial peptides. Two NF-κB signaling pathways, the Toll and the IMD pathways, are responsible for the induction of these antimicrobial peptides. Signal transduction in these pathways is strikingly similar to that in mammalian TLR pathways. In this chapter, we discuss in detail the molecular mechanisms of microbial recognition, signal transduction and NF-κB regulation, in both the Toll and the IMD pathways. Similarities and differences relative to their mammalian counterparts are discussed, and recent advances in our understanding of the intricate regulatory networks in these NF-κB signaling pathways are also highlighted.

The POU transcription factor Drifter/Ventral veinless regulates expression of Drosophila immune defense genes

Innate immunity operates as a first line of defense in multicellular organisms against infections caused by different classes of microorganisms. Antimicrobial peptides (AMPs) are synthesized constitutively in barrier epithelia to protect against microbial attack and are also upregulated in response to infection. Here, we implicate Drifter/Ventral veinless (Dfr/Vvl), a class III POU domain transcription factor, in tissue-specific regulation of the innate immune defense of Drosophila. We show that Dfr/Vvl is highly expressed in a range of immunocompetent tissues, including the male ejaculatory duct, where its presence overlaps with and drives the expression of cecropin, a potent broad-spectrum AMP. Dfr/Vvl overexpression activates transcription of several AMP genes in uninfected flies in a Toll pathway- and Imd pathway-independent manner. Dfr/Vvl activates a CecA1 reporter gene both in vitro and in vivo by binding to an upstream enhancer specific for the male ejaculatory duct. Further, Dfr/Vvl and the homeodomain protein Caudal (Cad) activate transcription synergistically via this enhancer. We propose that the POU protein Dfr/Vvl acts together with other regulators in a combinatorial manner to control constitutive AMP gene expression in a gene-, tissue-, and sex-specific manner, thus promoting a first-line defense against infection in tissues that are readily exposed to pathogens.

Identification and characterization of the parasitic wasp Nasonia defensins: positive selection targeting the functional region?

Defensin is a crucial component of innate immunity highly conserved across different insect orders. Here, we report identification and characterization of defensins in the parasitic wasp Nasonia (Hymenoptera: Pteromalidae). In comparison with those in the non-parasitic insect Apis mellifera, two different subtypes of defensins (defensin1 and defensin2) have undergone independent gene duplication to create a mutigene family of five members (named 1-1, 1-2, 2-1, 2-2 and 2-3) in the Nasonia lineage. Such duplication occurred before the divergence of three sibling species (N. vitripennis, N. giraulti and N. longicornis) and the duplicated genes was subsequently subjected to positive selection at the amino-terminal loop and the gamma-core region. RT-PCR identified that only the subtype 1 of defensins were constitutively expressed in the N. vitripennis adult stage and none of the five defensins was expressed in other developmental stages (i.e. the infected Musca domestica pupae). A functional form of 2-2 in N. vitripennis (named navidefensin2-2) was produced in Escherichia coli by an on-column refolding approach. The recombinant peptide presented a typical defensin structure, as identified by CD analysis, and selectively inhibited the growth of two Gram(+) bacteria at low micromolar concentrations. The bioactive surface responsible for antibacterial activity of navidefensin2-2 was identified in the gamma-core region of this molecule. Positive selection targeting the antibacterial region of defensins could be a consequence of evolutionary arms race between Nasonia and its pathogens.

GATA-4 is an angiogenic survival factor of the infarcted heart

BACKGROUND

Recent data suggest that GATA-4 is an antiapoptotic factor required for adaptive responses and a key regulator of hypertrophy and hypertrophy-associated genes in the heart. As a leading cause of chronic heart failure, reversal of postinfarction left ventricular remodeling represents an important target for therapeutic interventions. Here, we studied the role of GATA-4 as a mediator of postinfarction remodeling in rats.

METHODS AND RESULTS

Myocardial infarction, caused by ligating the left anterior descending coronary artery, significantly decreased the DNA binding activity of GATA-4 at day 1, whereas at 2 weeks the GATA-4 DNA binding was significantly upregulated. To determine the functional role of GATA-4, peri-infarct intramyocardial delivery of adenoviral vector expressing GATA-4 was done before left anterior descending coronary artery ligation. Hearts treated with GATA-4 gene transfer exhibited significantly increased ejection fraction and fractional shortening. Accordingly, infarct size was significantly reduced. To determine the cardioprotective mechanisms of GATA-4, myocardial angiogenesis, rate of apoptosis, c-kit+ cardiac stemlike cells, and genes regulated by GATA-4 were studied. The number of capillaries and stemlike cells was significantly increased, and decreased apoptosis was observed.

CONCLUSION

These results indicate that the reversal of reduced GATA-4 activity prevents adverse postinfarction remodeling through myocardial angiogenesis, antiapoptosis, and stem cell recruitment. GATA-4-based gene transfer may represent a novel, efficient therapeutic approach for heart failure.

Gene expression divergence and evolutionary analysis of the drosomycin gene family in Drosophila melanogaster

Drosomycin (Drs) encoding an inducible 44-residue antifungal peptide is clustered with six additional genes, Dro1, Dro2, Dro3, Dro4, Dro5, and Dro6, forming a multigene family on the 3L chromosome arm in Drosophila melanogaster. To get further insight into the regulation of each member of the drosomycin gene family, here we investigated gene expression patterns of this family by either microbe-free injury or microbial challenges using real time RT-PCR. The results indicated that among the seven drosomycin genes, Drs, Dro2, Dro3, Dro4, and Dro5 showed constitutive expressions. Three out of five, Dro2, Dro3, and Dro5, were able to be upregulated by simple injury. Interestingly, Drs is an only gene strongly upregulated when Drosophila was infected with microbes. In contrast to these five genes, Dro1 and Dro6 were not transcribed at all in either noninfected or infected flies. Furthermore, by 5' rapid amplification of cDNA ends, two transcription start sites were identified in Drs and Dro2, and one in Dro3, Dro4, and Dro5. In addition, NF-kappaB binding sites were found in promoter regions of Drs, Dro2, Dro3, and Dro5, indicating the importance of NF-kappaB binding sites for the inducibility of drosomycin genes. Based on the analyses of flanking sequences of each gene in D. melanogaster and phylogenetic relationship of drosomycins in D. melanogaster species-group, we concluded that gene duplications were involved in the formation of the drosomycin gene family. The possible evolutionary fates of drosomycin genes were discussed according to the combining analysis of gene expression pattern, gene structure, and functional divergence of these genes.

Cloning and characterization of Dorsal homologues in the hemipteran Rhodnius prolixus

Rhodnius prolixus is an ancient haematophagous hemipteran insect capable of mounting a powerful immune response. This response is transcriptionally regulated in part by transcription factors of the Rel/Nuclear Factor kappa B (Rel/NF-kappaB) family. We have cloned and characterized three members of this transcription factor family in this insect. Dorsal 1A is primarily expressed in early developmental stages. In contrast, dorsal 1B and 1C, both differentially spliced products of dorsal 1A, are expressed primarily in the adult fat body in response to septic injury, suggesting their exclusive role in immunity. Additionally, we identified putative kappaB binding sites in the 5' upstream regions of target genes known to be involved in the innate immune response of insects.

Immunity related genes in dipterans share common enrichment of AT-rich motifs in their 5' regulatory regions that are potentially involved in nucleosome formation

Background

Understanding the transcriptional regulation mechanisms in response to environmental challenges is of fundamental importance in biology. Transcription factors associated to response elements and the chromatin structure had proven to play important roles in gene expression regulation. We have analyzed promoter regions of dipteran genes induced in response to immune challenge, in search for particular sequence patterns involved in their transcriptional regulation.

Results

5' upstream regions of D. melanogaster and A. gambiae immunity-induced genes and their corresponding orthologous genes in 11 non-melanogaster drosophilid species and Ae. aegypti share enrichment in AT-rich short motifs. AT-rich motifs are associated with nucleosome formation as predicted by two different algorithms. In A. gambiae and D. melanogaster, many immunity genes 5' upstream sequences also showed NFκB response elements, located within 500 bp from the transcription start site. In A. gambiae, the frequency of ATAA motif near the NFκB response elements was increased, suggesting a functional link between nucleosome formation/remodelling and NFκB regulation of transcription.

Conclusion

AT-rich motif enrichment in 5' upstream sequences in A. gambiae, Ae. aegypti and the Drosophila genus immunity genes suggests a particular pattern of nucleosome formation/chromatin organization. The co-occurrence of such motifs with the NFκB response elements suggests that these sequence signatures may be functionally involved in transcriptional activation during dipteran immune response. AT-rich motif enrichment in regulatory regions in this group of co-regulated genes could represent an evolutionary constrained signature in dipterans and perhaps other distantly species.

DEAF-1 regulates immunity gene expression in Drosophila

Immunity genes are activated in the Drosophila fat body by Rel and GATA transcription factors. Here, we present evidence that an additional regulatory factor, deformed epidermal autoregulatory factor-1 (DEAF-1), also contributes to the immune response and is specifically important for the induction of two genes encoding antimicrobial peptides, Metchnikowin (Mtk) and Drosomycin (Drs). The systematic mutagenesis of a minimal Mtk 5' enhancer identified a sequence motif essential for both a response to LPS preparations in S2 cells and activation in the larval fat body in response to bacterial infection. Using affinity chromatography coupled to multidimensional protein identification technology (MudPIT), we identified DEAF-1 as a candidate regulator. DEAF-1 activates the expression of Mtk and Drs promoter-luciferase fusion genes in S2 cells. SELEX assays and footprinting data indicate that DEAF-1 binds to and activates Mtk and Drs regulatory DNAs via a TTCGGBT motif. The insertion of this motif into the Diptericin (Dpt) regulatory region confers DEAF-1 responsiveness to this normally DEAF-1-independent enhancer. The coexpression of DEAF-1 with Dorsal, Dif, and Relish results in the synergistic activation of transcription. We propose that DEAF-1 is a regulator of Drosophila immunity.

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.

Sequence structure and expression pattern of a novel anionic defensin-like gene from silkworm (Bombyx mori)

A defensin-like gene, BmdefA, was rediscovered in the silkworm genome and expressed sequence tags databases. The open reading frame of BmdefA encodes a prepropeptide consisting of a 22-residue signal peptide, a 34-residue propeptide, and a 36-residue mature peptide with a molecular mass of 4.0 kDa. The mature peptide possesses the characteristic six-cysteine motif of insect defensins, and its predicted isoelectric point is 4.12, indicating it is a novel anionic defensin. An intron is present in BmdefA and several cis-regulatory elements are in the regulating region. It is transcribed constitutively at a high level in the hemocyte, silk gland, head, and ovary of the silkworm larvae, and in the fat body of early-stage pupae and moth. BmdefA is also strongly induced by immune challenge. These results suggest that BmdefA plays an important role in both immunity and metamorphosis.

Identification and characterization of two novel lysozymes from Rhodnius prolixus, a vector of Chagas disease

Lysozymes have been described in invertebrates as digestive or immune molecules. We report here the characterization of two novel c-type lysozymes, RpLys-A (EU250274) and RpLys-B (EU250275), isolated from the fat body and digestive tract of immune stimulated Rhodnius prolixus, a major vector of Chagas disease. Transcriptional profiles indicate that the temporal and spatial expression patterns of these two peptides are very different. RpLys-A is expressed predominantly in the midgut after ingestion of Trypanosoma cruzi in a bloodmeal, or after injection of bacteria into the hemocoel. RpLys-B is expressed primarily in the fat body after bacterial injection. Phylogenetic alignments indicate that RpLys-A aligns best with molecules from other hemipterans whose major expression is found in the intestinal tract whereas RpLys-B aligns best with mosquito and tick molecules whose expression is found principally in hemocytes and fat body and whose role has been described as immune-related. These data suggest a differential compartmentalized role of two closely related molecules; one for immunity in the hemocoel and the other for digestion in the midgut.

Prominent down-regulation of storage protein genes after bacterial challenge in eri-silkworm, Samia cynthia ricini

We constructed two independent cDNA libraries from the fat body of Escherichia coli- or Candida albicans-challenged eri-silkworm Samia cynthia ricini larvae. We performed comparative expressed sequence tag (EST) analysis of the two cDNA libraries and found that two putative storage protein genes, ScSP1 and ScSP2, were markedly repressed by E. coli injection as compared with C. albicans injection. By quantitative real-time RT-PCR analysis, we showed that ScSP1 mRNA significantly reduced to 1/32-1/3 in the fat body of the female larvae, and ScSP2 mRNA reduced to 1/7-1/3 and 1/22-1/5 in the females and males, respectively, 12-36 h after E. coli injection as compared with PBS injection. In addition, SDS-PAGE analysis revealed that the accumulation of both the ScSP proteins in the larval hemolymph apparently decreased up to 36 h after E. coli injection. However, the amounts of the two ScSP proteins returned to the same level as those in the larvae injected with PBS by 48 h after injection, showing that the reduction in ScSPs caused by the bacterial challenge was transient. Moreover, potential binding sites for the Drosophila Rel/NF-kappaB protein Dorsal were found in the 5' upstream regulatory regions of ScSP1 and ScSP2, suggesting the participation of the Rel/NF-kappaB proteins in controlling the bacterial suppression of the ScSP genes. These results suggested the hypothesis that S. c. ricini has a genetic program to shut down temporarily dispensable gene expression in order to induce an acute and efficient expression of immune-related genes. These findings may provide new insight into the innate immune system in lepidopteran insects.

Characterization and expression of a cecropin-like gene from Helicoverpa armigera

A cDNA encoding a cecropin-like antibacterial peptide was obtained by RT-PCR from cotton budworm (Helicoverpa armigera). The cloned cDNA consists of 773 nucleotides with a 192 bp open reading frame encoding a peptide of 63 aa, which is comprised of a 21 aa signal peptide and a 42 amino acids mature peptide. The amino acid sequence of the mature peptide is highly similar to those D-type cecropins. The peptide was named as HacD. RT-PCR revealed that the transcript of HacD gene was inducible and could be detected in fatbodies, midguts, hemocytes and Malpighian tubules. HacD was highly expressed in E. coli M15 by fusing with green fluorescent protein (GFP). After purification, desalting and cleavage with factor Xa, HacD was released and showed antibacterial activity to both Gram-positive and Gram-negative bacteria. The genomic DNA of HacD was amplified by TAIL-PCR. NF-kappaB and NF-IL6 binding sites were found in the 5'-upstream regulatory region of HacD gene. EMSA (electrophoretic mobility shift assay) revealed that nuclear proteins from the immunized larvae could bind to the NF-kappaB site, but no nuclear proteins were found to bind to the NF-IL6 site. It was proposed that the NF-kappaB site might contribute to the expression of HacD.

A kappaB sequence code for pathway-specific innate immune responses

The Toll and Imd pathways induce humoral innate immune responses in Drosophila by activating NF-kappaB proteins that bind kappaB target sites. Here, we delineate a kappaB site sequence code that directs pathway-specific expression of innate immune loci. Using bioinformatic analysis of expression and sequence data, we identify shared properties of Imd- and Toll-specific response elements. Employing synthetic kappaB sites in luciferase reporter and in vitro binding assays, we demonstrate that the length of the (G)(n) element in the 5' half-site and of the central (A,T)-rich region combine to specify responsiveness to one or both pathways. We also show that multiple sites function to enhance the response to either or both pathways. Together, these studies elucidate the mechanism by which kappaB motifs direct binding by particular Drosophila NF-kappaB family members and thereby induce specialized innate immune repertoires.

The host defense of Drosophila melanogaster

To combat infection, the fruit fly Drosophila melanogaster relies on multiple innate defense reactions, many of which are shared with higher organisms. These reactions include the use of physical barriers together with local and systemic immune responses. First, epithelia, such as those beneath the cuticle, in the alimentary tract, and in tracheae, act both as a physical barrier and local defense against pathogens by producing antimicrobial peptides and reactive oxygen species. Second, specialized hemocytes participate in phagocytosis and encapsulation of foreign intruders in the hemolymph. Finally, the fat body, a functional equivalent of the mammalian liver, produces humoral response molecules including antimicrobial peptides. Here we review our current knowledge of the molecular mechanisms underlying Drosophila defense reactions together with strategies evolved by pathogens to evade them.

A multilayered defense against infection: combinatorial control of insect immune genes

The innate immune defense system involves the activity of endogenous antimicrobial peptides (AMPs), which inhibit the growth of most microbes. In insects, genes encoding AMPs are expressed at basal levels in barrier epithelia and are upregulated systemically in response to infection. To achieve this differentiated immune defense, Drosophila immune gene promoters combine tissue-specific enhancers and signal-dependent response elements. Transcription factors of the Hox, POU and GATA families control tissue-specific expression of AMP genes, either constitutively or in combination with NF-kappaB/Rel family factors that function as 'on-off switches' during infection. Here, we review these different modes of AMP expression and provide a model for transcriptional regulation of AMP genes.

Isolation of regulators of Drosophila immune defense genes by a double interaction screen in yeast

Innate immunity is a universal and ancient defense system in metazoans against microorganisms. Antimicrobial peptides, which are synthesized both in insects and humans, constitute an endogenous, gene-encoded defense arsenal. In Drosophila, antimicrobial peptides, such as the potent cecropins, are expressed both constitutively in barrier epithelia, as well as systemically in response to infection. Rel/NF-kappaB proteins are well-known regulators of antimicrobial peptide genes, but very few Rel/NF-kappaB co-factors and/or tissue-specific regulators have been identified. We performed a double interaction screen in yeast to isolate Drosophila cDNAs coding for direct regulators, as well as Dif co-regulators, of the CecropinA1 gene. Three classes of positive cDNA clones corresponding to 15 Drosophila genes were isolated and further characterized. One of the Dif-independent cDNAs encoded the Rel/NF-kappaB protein Relish; a well-known activator of antimicrobial peptide genes in Drosophila, demonstrating the applicability of this type of screen for isolating regulators of immune defense. Most interestingly, three transcription factors belonging to the POU domain class of homeodomain proteins, Pdm1, Pdm2 and Dfr/Vvl were isolated as Dif-interacting partners, and subsequently verified as regulators of CecA1 expression in Drosophila cells. The importance of POU proteins in development and differentiation in Drosophila and mammals is well documented, but their role in regulation of Drosophila immune defense genes is a new and essential finding.

Keeping up NF-κB appearances: Epigenetic control of immunity or inflammation-triggered epigenetics

Controlled expression of cytokine genes is an essential component of an immune response and is crucial for homeostasis. In order to generate an appropriate response to an infectious condition, the type of cytokine, as well as the cell type, dose range and the kinetics of its expression are of critical importance. The nuclear factor-kappaB (NF-kappaB) family of transcription factors has a crucial role in rapid responses to stress and pathogens (innate immunity), as well as in development and differentiation of immune cells (acquired immunity). Although quite a number of genes contain NF-kappaB-responsive elements in their regulatory regions, their expression pattern can significantly vary from both a kinetic and quantitative point of view, reflecting the impact of environmental and differentiative cues. At the transcription level, selectivity is conferred by the expression of specific NF-kappaB subunits and their respective posttranslational modifications, and by combinatorial interactions between NF-kappaB and other transcription factors and coactivators, that form specific enhanceosome complexes in association with particular promoters. These enhanceosome complexes represent another level of signaling integration, whereby the activities of multiple upstream pathways converge to impress a distinct pattern of gene expression upon the NF-kappaB-dependent transcriptional network. Today, several pieces of evidence suggest that the chromatin structure and epigenetic settings are the ultimate integration sites of both environmental and differentiative inputs, determining proper expression of each NF-kappaB-dependent gene. We will therefore discuss in this review the multilayered interplay of NF-kappaB signaling and epigenome dynamics, in achieving appropriate gene expression responses and transcriptional activity.

A novel association between clustered NF-kappaB and C/EBP binding sites is required for immune regulation of mosquito Defensin genes

A comparative analysis identified key cis-acting regulatory elements responsible for the temporal control of mosquito Defensin gene expression. The promoters of Anopheles gambiae Defensin 1 and two isoforms of Aedes aegypti Defensin A are up-regulated by immune challenge. This stimulated activity depends upon a cluster of three NF-kappaB binding sites and closely associated C/EBP-like motifs, which function as a unit for optimal promoter activity. Binding of NF-kappaB and C/EBP like transcription factors is confirmed by electrophoretic mobility shift assay, including supershifts with antibodies to C/EBP. KappaB-like motifs are abundant within antimicrobial peptide gene promoters and most are very closely associated with putative C/EBP binding sites. This novel association between NF-kappaB and C/EBP binding sites may, therefore, be of widespread significance.

Cooperative control of Drosophila immune responses by the JNK and NF-kappaB signaling pathways

Jun N-terminal kinase (JNK) signaling is a highly conserved pathway that controls both cytoskeletal remodeling and transcriptional regulation in response to a wide variety of signals. Despite the importance of JNK in the mammalian immune response, and various suggestions of its importance in Drosophila immunity, the actual contribution of JNK signaling in the Drosophila immune response has been unclear. Drosophila TAK1 has been implicated in the NF-kappaB/Relish-mediated activation of antimicrobial peptide genes. However, we demonstrate that Relish activation is intact in dTAK1 mutant animals, and that the immune response in these mutant animals was rescued by overexpression of a downstream JNKK. The expression of a JNK inhibitor and induction of JNK loss-of-function clones in immune responsive tissue revealed a general requirement for JNK signaling in the expression of antimicrobial peptides. Our data indicate that dTAK1 is not required for Relish activation, but instead is required in JNK signaling for antimicrobial peptide gene expression.

A transgenic silkworm expressing the immune-inducible cecropin B-GFP reporter gene

To analyze cecropin B promoter (P-CecB) activity in vivo, we constructed transgenic silkworms that expressed EGFP under the control of P-CecB using the piggyBac transposable element. Genomic Southern blot analysis of the G1 and G2 generations indicated the stable insertion of EGFP in the genome. Injection of Escherichia coli cells into the larvae strongly induced EGFP expression in the fat bodies and all five hemocyte cell types. Northern blot analysis indicated that the expression kinetics of EGFP in the fat bodies following bacterial injection were correlated with that of endogenous CecB. Flow cytometric analysis of the hemocytes revealed that EGFP expression was increased by bacteria, but not by yeast. Our results indicate that the features of EGFP expression in the transgenic silkworm are equivalent to those of endogenous CecB and that P-CecB activation can be monitored by EGFP expression using transgenic silkworms.

Structures, regulatory regions, and inductive expression patterns of antimicrobial peptide genes in the silkworm Bombyx mori

Antimicrobial peptides (AMPs) are a group of immune proteins that protect the host from infection. In Drosophila, seven groups of inducible AMPs have been identified, with activities against fungi and gram-positive and gram-negative bacteria. On the basis of the silkworm genome sequence and expressed sequence tags, we identified 35 AMP genes, mostly belonging to the cecropin, moricin, and gloverin gene families. We predicted the core promoters required for gene transcription and the cis-regulatory elements for NF-kappaB/Rel and GATA transcription factors. The expression profiles of these genes after an immune challenge with lipopolysaccharide were examined by reverse transcription PCR. Members of the cecropin B and gloverin A subfamilies were intensely expressed in the fat body after induction. In contrast, those of the moricin B subfamily were not expressed under the same conditions. Such results suggest that these regulatory elements and their positions in the upstream regions play an important role in regulating the transcription of these defense genes.

The therapeutic potential of cationic peptides

Novel classes of antibiotics that are useful against resistant bacteria are a major need in human medicine. Cationic antimicrobial peptides are utilised as nature's antibiotics, being produced constitutively or in response to infection in virtually every type of organism from plants and insects to man. Thus, these peptides are now being considered as potential antibiotics for infections. They have the following assets: structural diversity, rapid bactericidal action, a broad spectrum of activity that includes most of the clinically important resistant pathogens, and several ancillary activities which can include antifungal, antiviral, anti-endotoxin activities, and promotion of wound healing. Cationic peptides and proteins are now proceeding through clinical trials as topical antibiotics and anti-endotoxins.

Nutritional regulation of vitellogenesis in mosquitoes: implications for anautogeny

Anautogeny is a successful reproductive strategy utilized by many mosquito species and other disease-transmitting arthropod vectors. Developing an understanding of the mechanisms underlying anautogeny in mosquitoes is very important because this reproductive strategy is the driving force behind the transmission of disease to millions of people. Information gained from mosquito studies may also be applicable to other blood feeding insect vectors. The conversion of protein from blood into yolk protein precursors for the developing oocytes is an essential part of the reproductive cycle, and understanding how this process is regulated could lead to safe, specific, and effective ways to block reproduction in blood feeding insects. Great gains have been made in elucidating the mechanisms that regulate vitellogenesis in mosquitoes, especially Ae. aegypti. However, a number of questions remain to be answered to make the picture more complete. In this review, we summarize what is currently known about the nutritional regulation of vitellogenesis in mosquitoes and the questions that remain to be answered about this important biological phenomenon.

Manduca sexta prophenoloxidase activating proteinase-1 (PAP-1) gene: organization, expression, and regulation by immune and hormonal signals

Insect phenoloxidase (PO) participates in melanotic encapsulation, wound healing, and cuticle sclerotization. It is converted from prophenoloxidase (proPO) by a proPO-activating proteinase (PAP). Manduca sexta PAP-1, the final component of a serine proteinase cascade, cleaves proPO to generate active PO. In an effort to understand the transcriptional regulation, we isolated a genomic clone of the PAP-1 gene, determined its nucleotide sequence, and elucidated its exon-intron organization. Computer analysis revealed several immune and hormone responsive elements in the upstream region. Southern blot analysis suggested that the M. sexta genome contains a single copy of PAP-1 gene. Reverse transcription-polymerase chain reaction showed that PAP-1 was constitutively expressed in fat body, trachea, and nerve tissue of the fifth instar larvae. The mRNA levels in hemocytes and fat body markedly increased in response to a bacterial challenge. We also observed tissue-specific and developmental regulation of the gene's transcription. Treating M. sexta fat body culture with 20-hydroxyecdysone reduced the PAP-1 mRNA level. These data indicated that the expression of PAP-1 gene is under the dual control of immune and hormonal signals.

Characterization of a homologue of the Rel/NF-kappaB transcription factor from a beetle, Allomyrina dichotoma

A cDNA encoding a Rel/NF-kappaB homologue was cloned from a beetle, Allomyrina dichotoma, by reverse transcriptase-polymerase chain reactions (RT-PCR) taking advantage of the conserved Rel homology domain (RHD) to synthesize primers. The Rel/NF-kappaB homologue was designated A. dichotoma (A.d.) Rel A. The amino acid sequence of the A.d. Rel A RHD was compared with those of insect RHDs. The result showed that it has 70% identity with Tribolium castaneum Dorsal, 66% with Drosophila melanogaster Dorsal, 61% with Anopheles gambiae Gambif1, and 55% with D. melanogaster Dif. A putative phosphorylation site in the RHD, RRPS, and two putative nuclear localization signals were conserved in A.d. Rel A. A recombinant fusion protein containing the A.d. Rel A RHD was confirmed to bind specifically to the NF-kappaB site of a gene encoding A.d. coleoptericin A, an antibacterial peptide from A. dichotoma. The activity of A.d. Rel A in modulating a gene construct of the A.d. coleoptericin A promoter-luciferase reporter by expressing the A.d. coleoptericin A cDNA in a Bombyx mori cell line was analyzed. The result showed that A.d. Rel A strongly activates the A.d. coleoptericin A gene construct, whereas A.d. Rel A failed to activate the gene construct containing the mutated NF-kappaB site, suggesting the importance of the interaction between the NF-kappaB site and A.d. Rel A in the signal transduction for gene expression of antibacterial peptides in A. dichotoma.

Immunity regulatory DNAs share common organizational features in Drosophila

Infection results in the rapid activation of immunity genes in the Drosophila fat body. Two classes of transcription factors have been implicated in this process: the REL-containing proteins, Dorsal, Dif, and Relish, and the GATA factor Serpent. Here we present evidence that REL-GATA synergy plays a pervasive role in the immune response. SELEX assays identified consensus binding sites that permitted the characterization of several immunity regulatory DNAs. The distribution of REL and GATA sites within these DNAs suggests that most or all fat-specific immunity genes contain a common organization of regulatory elements: closely linked REL and GATA binding sites positioned in the same orientation and located near the transcription start site. Aspects of this "regulatory code" are essential for the immune response. These results suggest that immunity regulatory DNAs contain constrained organizational features, which may be a general property of eukaryotic enhancers.

Functional characterization of a novel promoter element required for an innate immune response in Drosophila

Innate immune reactions are crucial processes of metazoans to protect the organism against overgrowth of faster replicating microorganisms. Drosophila melanogaster is a precious model for genetic and molecular studies of the innate immune system. In response to infection, the concerted action of a battery of antimicrobial peptides ensures efficient killing of the microbes. The induced gene expression relies on translocation of the Drosophila Rel transcription factors Relish, Dif, and Dorsal to the nucleus where they bind to kappaB-like motifs in the promoters of the inducible genes. We have identified another putative promoter element, called region 1 (R1), in a number of antimicrobial peptide genes. Site-directed mutagenesis of the R1 site diminished Cecropin A1 (CecA1) expression in transgenic Drosophila larvae and flies. Infection of flies induced a nuclear R1-binding activity that was unrelated to the kappaB-binding activity in the same extracts. Although the R1 motif was required for Rel protein-mediated CecA1 expression in cotransfection experiments, our data argue against it being a direct target for the Drosophila Rel proteins. We propose that the R1 and kappaB motifs are targets for distinct regulatory complexes that act in concert to promote high levels of antimicrobial peptide gene expression in response to infection.

Genomic structure and expression analysis of the gene encoding a silkworm basic Kunitz-type chymotrypsin inhibitor

Kunitz-type chymotrypsin inhibitor CIb1 of silkworm Bombyx mori is a basic peptide consisting of 62 amino acid residues. To elucidate the mechanisms of transcriptional regulation of CIb1 gene expression, we cloned it for genomic structure analysis. CIb1 cDNA was used as a probe to screen a BAC sub-library. One positive clone containing the upstream sequences was isolated and the sequence result showed that CIb1 gene consists of three exons spaced by two introns. In the 5'-flanking region, consensus TATA and CCAAT boxes were identified. Other binding sites for transcription factors such as NF-kappaB, GATA, C/EBP, COUP-TF/HNF-4, RORalpha1, SRY, and HOXA3 were also detected. Southern blot analysis suggested a single copy of CIb1 gene in the silkworm genome. Northern blot analysis indicated that the expression of CIb1 gene is transcriptionally regulated during development and is apparently tissue-specific. The CIb1 mRNA was detected in fat body, ovary, trachea, and skin. We furthermore investigated the CIb1 expression profiles after LPS and E. coli injection. The fluctuations of CIb1 transcript in challenged larvae confirm our proposal that CIb1 is an immune responsible gene. According to our data, we discussed the transcriptional factors putatively responsible for the physiological role of CIb1 in the silkworm hemolymph.

Regulation of antibacterial and antifungal innate immunity in fruitflies and humans

Insects have been very successful in adapting to their environment, and the ability of the insect immune system to detect and elicit the appropriate response against various invading pathogens has helped in this success. Unlike the vertebrate immune system, which consists of both innate and adaptive components, insect immunity probably consists entirely of an innate immune response, as no evidence of an adaptive response has been found. The innate immune response is described as either a reaction against "lack of self," or the interaction between host germline-encoded receptors and molecules unique to a particular class of invading organisms. Once the invading organism is recognized, the host immune response can be activated via signaling pathways that lead to the appropriate reaction. This review endeavors to put forth how through genetic, molecular, and biochemical studies of the fruit fly Drosophila melanogaster, as well as other insects, it is now understood that aspects of the insect and vertebrate innate immune system are very similar.

Characterization of genomic DNA encoding cecropins from an Aedes albopictus mosquito cell line

We used cDNA probes from Aedes albopictus mosquito cecropins AalCecA, B, and C to obtain genomic DNA copies and flanking DNA. Two gene copies (AalCecA1 and A2, AalCecB1 and B2, AalCecC1 and C2) encoding each of the three mature cecropin peptides were recovered. All these genes had a similar organization, into two exons interrupted by a single short intron. AalCecA1 and AalCecA2 encode mature protein products that differ by one amino acid residue, while AalCecB1 and AalCecB2, AalCecC1 and AalCecC2 encode identical mature cecropin peptides, respectively. The AalCecB and C gene pairs each share a common intergenic region of approximately 1 kb, with the two coding regions transcribed in opposite directions. With the exception of small insertions/deletions, the intergenic spacer region was highly conserved between the B1/C1 and B2/C2 clones. In transfected cells, 0.8 kb of upstream sequence was sufficient for inducible expression of AalCecA1. Within this region, a 28 bp sequence at positions -192 to -165 upstream of the transcription initiation site was found to contain a potential regulatory element. In electrophoretic mobility shift assays, synthetic double-stranded DNA containing this 28 bp sequence retarded protein in cytoplasmic and nuclear extracts from C7-10 cells.

The GATA factor Serpent is required for the onset of the humoral immune response in Drosophila embryos

Innate immunity in Drosophila is characterized by the inducible expression of antimicrobial peptides. We have investigated the development and regulation of immune responsiveness in Drosophila embryos after infection. Immune competence, as monitored by the induction of Cecropin A1-lacZ constructs, was observed first in the embryonic yolk. This observation suggests that the yolk plays an important role in the humoral immune response of the developing embryo by synthesizing antimicrobial peptides. Around midembryogenesis, the response in the yolk was diminished. Simultaneously, Cecropin expression became inducible in a large number of cells in the epidermis, demonstrating that late-stage embryos can synthesize their own antibiotics in the epidermis. This production likely serves to provide the hatching larva with an active antimicrobial barrier and protection against systemic infections. Cecropin expression in the yolk required the presence of a GATA site in the promoter as well as the involvement of the GATA-binding transcription factor Serpent (dGATAb). In contrast, neither the GATA site nor Serpent were necessary for Cecropin expression in the epidermis. Thus, the inducible immune responses in the yolk and in the epidermis can be uncoupled and call for distinct sets of transcription factors. Our data suggest that Serpent is involved in the distinction between a systemic response in the yolk/fat body and a local immune response in epithelial cells. In addition, the present study shows that signal transduction pathways controlling innate and epithelial defense reactions can be dissected genetically in Drosophila embryos.