Honey bee (Apis mellifera) transferrin-gene structure and the role of ecdysteroids in the developmental regulation of its expression

Fat body-derived juvenile hormone acid methyltransferase functions to maintain iron homeostasis in Drosophila melanogaster

Iron homeostasis is of critical importance to living organisms. Drosophila melanogaster has emerged as an excellent model to study iron homeostasis, while the regulatory mechanism of iron metabolism remains poorly understood. Herein, we accidently found that knockdown of juvenile hormone (JH) acid methyltransferase (Jhamt) specifically in the fat body, a key rate-limiting enzyme for JH synthesis, led to iron accumulation locally, resulting in serious loss and dysfunction of fat body. Jhamt knockdown-induced phenotypes were mitigated by iron deprivation, antioxidant and Ferrostatin-1, a well-known inhibitor of ferroptosis, suggesting ferroptosis was involved in Jhamt knockdown-induced defects in the fat body. Further study demonstrated that upregulation of Tsf1 and Malvolio (Mvl, homolog of mammalian DMT1), two iron importers, accounted for Jhamt knockdown-induced iron accumulation and dysfunction of the fat body. Mechanistically, Kr-h1, a key transcription factor of JH, acts downstream of Jhamt inhibiting Tsf1 and Mvl transcriptionally. In summary, the findings indicated that fat body-derived Jhamt is required for the development of Drosophila by maintaining iron homeostasis in the fat body, providing unique insight into the regulatory mechanisms of iron metabolism in Drosophila.

Detailed chemical analysis of honey bee (Apis mellifera) worker brood volatile profile from egg to emergence

Chemical communication is a widely used mode of communication for social insects and has been demonstrated to be involved in many behaviours and physiological processes such as reproduction, nutrition or the fight against parasites and pathogens. In the honey bee, Apis mellifera, the release of chemical compounds by the brood plays a role in worker behaviour, physiology, and foraging activities and colony health as a whole. Several compounds have already been described as brood pheromones, such as components of the brood ester pheromone and (E)-β-ocimene. Several other compounds originating from diseased or varroa-infested brood cells have been described as triggering the hygienic behaviour of workers. So far, studies of brood emissions have focused on specific stages of development and little is known about the emission of volatile organic compounds by the brood. In this study, we investigate the semiochemical profile of worker honey bee brood during its whole developmental cycle, from egg to emergence, with a specific focus on volatile organic compounds. We describe variation in emissions of thirty-two volatile organic compounds between brood stages. We highlight candidate compounds that are particularly abundant in specific stages and discuss their potential biological significance.

Transferrin-mediated iron sequestration suggests a novel therapeutic strategy for controlling Nosema disease in the honey bee, Apis mellifera

Nosemosis C, a Nosema disease caused by microsporidia parasite Nosema ceranae, is a significant disease burden of the European honey bee Apis mellifera which is one of the most economically important insect pollinators. Nevertheless, there is no effective treatment currently available for Nosema disease and the disease mechanisms underlying the pathological effects of N. ceranae infection in honey bees are poorly understood. Iron is an essential nutrient for growth and survival of hosts and pathogens alike. The iron tug-of-war between host and pathogen is a central battlefield at the host-pathogen interface which determines the outcome of an infection, however, has not been explored in honey bees. To fill the gap, we conducted a study to investigate the impact of N. ceranae infection on iron homeostasis in honey bees. The expression of transferrin, an iron binding and transporting protein that is one of the key players of iron homeostasis, in response to N. ceranae infection was analysed. Furthermore, the functional roles of transferrin in iron homeostasis and honey bee host immunity were characterized using an RNA interference (RNAi)-based method. The results showed that N. ceranae infection causes iron deficiency and upregulation of the A. mellifera transferrin (AmTsf) mRNA in honey bees, implying that higher expression of AmTsf allows N. ceranae to scavenge more iron from the host for its proliferation and survival. The suppressed expression levels of AmTsf via RNAi could lead to reduced N. ceranae transcription activity, alleviated iron loss, enhanced immunity, and improved survival of the infected bees. The intriguing multifunctionality of transferrin illustrated in this study is a significant contribution to the existing body of literature concerning iron homeostasis in insects. The uncovered functional role of transferrin on iron homeostasis, pathogen growth and honey bee's ability to mount immune responses may hold the key for the development of novel strategies to treat or prevent diseases in honey bees.

Isolation of ferritin and its interaction with BmNPV in the silkworm, Bombyx mori

Ferritin is a ubiquitous iron storage protein that plays an important role in host defence against pathogen infections. In the present study, native ferritin was isolated from the hemolymph of Bombyx mori using native-polyacrylamide gel electrophoresis (native-PAGE) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The results revealed that ferritin consisted of two subunits, designated as BmFerHCH and BmFerLCH. Previously integrated previous transcriptome and iTRAQ data showed that the two subunits were down-regulated in resistant silkworm strain BC9 and there was no obvious change in the expression levels of the subunits in susceptible silkworm strain P50 after BmNPV infection. Virus overlay assays revealed that B. mori ferritin as the form of heteropolymer had an interaction with B. mori nucleopolyhedrovirus (BmNPV), but it can't interact with BmNPV after depolymerisation. What's more, reverse transcription quantitative PCR (RT-qPCR) analysis suggested that BmFerHCH and BmFerLCH could be induced by bacteria, virus and iron. This is the first study to extract B. mori ferritin successfully and confirms their roles in the process of BmNPV infection. All these results will lay a foundation for further research the function of B. mori ferritin.

Transcriptome profiling of the honeybee parasite Varroa destructor provides new biological insights into the mite adult life cycle

Background

The parasite Varroa destructor represents a significant threat to honeybee colonies. Indeed, development of Varroa infestation within colonies, if left untreated, often leads to the death of the colony. Although its impact on bees has been extensively studied, less is known about its biology and the functional processes governing its adult life cycle and adaptation to its host. We therefore developed a full life cycle transcriptomic catalogue in adult Varroa females and included pairwise comparisons with males, artificially-reared and non-reproducing females (10 life cycle stages and conditions in total).

Results

Extensive remodeling of the Varroa transcriptome was observed, with an upregulation of energetic and chitin metabolic processes during the initial and final phases of the life cycle (e.g. phoretic and post-oviposition stages), whereas during reproductive stages in brood cells genes showing functions related to transcriptional regulation were overexpressed. Several neurotransmitter and neuropeptide receptors involved in behavioural regulation, as well as active compounds of salivary glands, were also expressed at a higher level outside the reproductive stages. No difference was detected between artificially-reared phoretic females and their counterparts in colonies, or between females who failed to reproduce and females who successfully reproduced, indicating that phoretic individuals can be reared outside host colonies without impacting their physiology and that mechanisms underlying reproductive failure occur before oogenesis.

Conclusions

We discuss how these new findings reveal the remarkable adaptation of Varroa to its host biology and notably to the switch from living on adults to reproducing in sealed brood cells. By spanning the entire adult life cycle, our work captures the dynamic changes in the parasite gene expression and serves as a unique resource for deciphering Varroa biology and identifying new targets for mite control.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4668-z) contains supplementary material, which is available to authorized users.

A transferrin gene associated with development and 2-tridecanone tolerance in Helicoverpa armigera

The full-length cDNA (2320 bp) encoding a putative iron-binding transferrin protein from Helicoverpa armigera was cloned and named HaTrf. The putative HaTrf sequence included 670 amino acids with a molecular mass of approximately 76 kDa. Quantitative PCR results demonstrated that the transcriptional level of HaTrf was significantly higher in the sixth instar and pupa stages as compared with other developmental stages. HaTrf transcripts were more abundant in fat bodies and in the epidermis than in malpighian tubules. Compared with the control, the expression of HaTrf increased dramatically 24 h after treatment with 2-tridecanone. Apparent growth inhibition with a dramatic body weight decrease was observed in larvae fed with HaTrf double-stranded RNA (dsRNA), as compared with those fed with green fluorescent protein dsRNA. RNA interference of HaTrf also significantly increased the susceptibility of larvae to 2-tridecanone. These results indicate the possible involvement of HaTrf in tolerance to plant secondary chemicals.

Production of the catechol type siderophore bacillibactin by the honey bee pathogen Paenibacillus larvae

The Gram-positive bacterium Paenibacillus larvae is the etiological agent of American Foulbrood. This bacterial infection of honey bee brood is a notifiable epizootic posing a serious threat to global honey bee health because not only individual larvae but also entire colonies succumb to the disease. In the recent past considerable progress has been made in elucidating molecular aspects of host pathogen interactions during pathogenesis of P. larvae infections. Especially the sequencing and annotation of the complete genome of P. larvae was a major step forward and revealed the existence of several giant gene clusters coding for non-ribosomal peptide synthetases which might act as putative virulence factors. We here present the detailed analysis of one of these clusters which we demonstrated to be responsible for the biosynthesis of bacillibactin, a P. larvae siderophore. We first established culture conditions allowing the growth of P. larvae under iron-limited conditions and triggering siderophore production by P. larvae. Using a gene disruption strategy we linked siderophore production to the expression of an uninterrupted bacillibactin gene cluster. In silico analysis predicted the structure of a trimeric trithreonyl lactone (DHB-Gly-Thr)3 similar to the structure of bacillibactin produced by several Bacillus species. Mass spectrometric analysis unambiguously confirmed that the siderophore produced by P. larvae is identical to bacillibactin. Exposure bioassays demonstrated that P. larvae bacillibactin is not required for full virulence of P. larvae in laboratory exposure bioassays. This observation is consistent with results obtained for bacillibactin in other pathogenic bacteria.

Alternative splicing contributes to the coordinated regulation of ferritin subunit levels in Bactrocera dorsalis (Hendel)

A constant ratio of ferritin heavy chain homolog (HCH) and light chain homolog (LCH) subunits seems to be required to compose the ferritin heteropolymer protein in insects. However, the mechanism by which insect LCH genes regulate protein levels remains unclear. We report that alternative promoters and alternative splicing contribute to maintaining a constant ratio of the two subunits, BdFer1HCH and BdFer2LCH (ferritin 1 HCH and ferritin 2 LCH), in Bactrocera dorsalis, a notorious quarantine pest. The genes BdFer1HCH and BdFer2LCH were identified with a series of potential transcription factor binding sites and were shown to be clustered within the genome in a "head to head" fashion. Thus, we unearthed a potential post-transcriptional mechanism to regulate the levels of LCH subunits, and confirmed that the expressions of BdFer1HCH and BdFer2LCH were induced by 20-hydroecdysone, iron overload, and immune challenge.

Nutritionally driven differential gene expression leads to heterochronic brain development in honeybee castes

The differential feeding regimes experienced by the queen and worker larvae of the honeybee Apis mellifera shape a complex endocrine response cascade that ultimately gives rise to differences in brain morphologies. Brain development analyzed at the morphological level from the third (L3) through fifth (L5) larval instars revealed an asynchrony between queens and workers. In the feeding phase of the last larval instar (L5F), two well-formed structures, pedunculi and calyces, are identifiable in the mushroom bodies of queens, both of which are not present in workers until a later phase (spinning phase, L5S). Genome-wide expression analyses and normalized transcript expression experiments monitoring specific genes revealed that this differential brain development starts earlier, during L3. Analyzing brains from L3 through L5S1 larvae, we identified 21 genes with caste-specific transcription patterns (e.g., APC-4, GlcAT-P, fax, kr-h1 and shot), which encode proteins that are potentially involved in the development of brain tissues through controlling the cell proliferation rate (APC4, kr-h1) and fasciculation (GlcAT-P, fax, and shot). Shot, whose expression is known to be required for axon extension and cell proliferation, was found to be transcribed at significantly higher levels in L4 queens compared with worker larvae. Moreover, the protein encoded by this gene was immunolocalized to the cytoplasm of cells near the antennal lobe neuropiles and proximal to the Kenyon cells in the brains of L4 queens. In conclusion, during the larval period, the brains of queens are larger and develop more rapidly than workers’ brains, which represents a developmental heterochrony reflecting the effect of the differential feeding regime of the two castes on nervous system development. Furthermore, this differential development is characterized by caste-specific transcriptional profiles of a set of genes, thus pointing to a link between differential nutrition and differential neurogenesis via genes that control cell proliferation and fasciculation.

Bacterial infection activates the immune system response and dysregulates microRNA expression in honey bees

In insects, a rapid and massive synthesis of antimicrobial peptides (AMPs) is activated through signaling pathways (Toll and Imd) to combat invading microbial pathogens. However, it is still unclear whether different types of bacteria provoke specific responses. Immune response mechanisms and the activation of specific genes were investigated by challenging Apis mellifera workers with the Gram-negative bacterium Serratia marcescens or the Gram-positive bacterium Micrococcus luteus. The immune system responded by activating most genes of the Toll and Imd pathways, particularly AMP genes. However, genes specifically regulated by M. luteus or S. marcescens were not detected, suggesting an interaction between the signaling pathways that lead to immune effectors synthesis. Despite this finding, kappaB motifs in the 5'-UTRs of selected genes suggest a pathway-specific control of AMP and transferrin-1 gene expression. Regulation by miRNAs was also investigated and revealed a number of candidates for the post-transcriptional regulation of immune genes in bees.

Insect transferrins: multifunctional proteins

BACKGROUND

Many studies have been done evaluating transferrin in insects. Genomic analyses indicate that insects could have more than one transferrin. However, the most commonly studied insect transferrin, Tsf1, shows greatest homology to mammalian blood transferrin.

SCOPE OF REVIEW

Aspects of insect transferrin structure compared to mammalian transferrin and the roles transferrin serves in insects are discussed in this review.

MAJOR CONCLUSIONS

Insect transferrin can have one or two lobes, and can bind iron in one or both. The iron binding ligands identified for the lobes of mammalian blood transferrin are generally conserved in the lobes of insect transferrins that have an iron binding site. Available information supports that the form of dietary iron consumed influences the regulation of insect transferrin. Although message is expressed in several tissues in many insects, fat body is the likely source of hemolymph transferrin. Insect transferrin is a vitellogenic protein that is down-regulated by Juvenile Hormone. It serves a role in transporting iron to eggs in some insects, and transferrin found in eggs appears to be endowed from the female. In addition to the roles of transferrin in iron delivery, this protein also functions to reduce oxidative stress and to enhance survival of infection.

GENERAL SIGNIFICANCE

Future studies in Tsf1 as well as the other insect transferrins that bind iron are warranted because of the roles of transferrin in preventing oxidative stress, enhancing survival to infections and delivering iron to eggs for development. This article is part of a Special Issue entitled Transferrins: Molecular mechanisms of iron transport and disorders.

Molecular evolution of the transferrin family and associated receptors

BACKGROUND

In vertebrates, serum transferrins are essential iron transporters that have bind and release Fe(III) in response to receptor binding and changes in pH. Some family members such as lactoferrin and melanotransferrin can also bind iron while others have lost this ability and have gained other functions, e.g., inhibitor of carbonic anhydrase (mammals), saxiphilin (frogs) and otolith matrix protein 1 (fish).

SCOPE OF REVIEW

This article provides an overview of the known transferrin family members and their associated receptors and interacting partners.

MAJOR CONCLUSIONS

The number of transferrin genes has proliferated as a result of multiple duplication events, and the resulting paralogs have developed a wide array of new functions. Some homologs in the most primitive metazoan groups resemble both serum and melanotransferrins, but the major yolk proteins show considerable divergence from the rest of the family. Among the transferrin receptors, the lack of TFR2 in birds and reptiles, and the lack of any TFR homologs among the insects draw attention to the differences in iron transport and regulation in those groups.

GENERAL SIGNIFICANCE

The transferrin family members are important because of their clinical significance, interesting biochemical properties, and evolutionary history. More work is needed to better understand the functions and evolution of the non-vertebrate family members. This article is part of a Special Issue entitled Molecular Mechanisms of Iron Transport and Disorders.

Molecular cloning and characterization of a transferrin cDNA from the white-spotted flower chafer,Protaetia brevitarsis

A full-length cDNA clone with high homology to insect transferrin genes was cloned by screening a Protaetia brevitarsis cDNA library. This gene (PbTf) had a total length of 2338 bp with an open reading frame (ORF) of 2163 bp, and encoded a predicted peptide of 721 amino acid residues. Like known cockroach, termite, and beetle transferrins, PbTf appears to have residues comprising iron-binding sites in both N- and C-terminal lobes. The deduced amino acid sequence of the PbTf cDNA was closest in structure to the beetle Apriona germari transferrin (68% protein sequence identity). Northern blot analysis revealed that PbTf exhibited fat body-specific expression and was upregulated by wounding, bacterial or fungal infection and iron overload, suggesting a functional role for PbTf in defense and stress responses.

Coordinated responses to developmental hormones in the Kenyon cells of the adult worker honey bee brain (Apis mellifera L.)

The brains of experienced forager honey bees exhibit predictable changes in structure, including significant growth of the neuropil of the mushroom bodies. In vertebrates, members of the superfamily of nuclear receptors function as key regulators of neuronal structure. The adult insect brain expresses many members of the nuclear receptor superfamily, suggesting that insect neurons are also likely important targets of developmental hormones. The actions of developmental hormones (the ecdysteroids and the juvenile hormones) in insects have been primarily explored in the contexts of metamorphosis and vitellogenesis. The cascade of gene expression activated by 20-hydroxyecdysone and modulated by juvenile hormone is strikingly conserved in these different physiological contexts. We used quantitative RT-PCR to measure, in the mushroom bodies of the adult worker honey bee brain, relative mRNA abundances of key members of the nuclear receptor superfamily (EcR, USP, E75, Ftz-f1, and Hr3) that participate in the metamorphosis/vitellogenesis cascade. We measured responses to endogenous peaks of hormones experienced early in adult life and to exogenous hormones. Our studies demonstrate that a population of adult insect neurons is responsive to endocrine signals through the use of conserved portions of the canonical ecdysteroid transcriptional cascade previously defined for metamorphosis and vitellogenesis.

Molecular characterization of iron binding proteins, transferrin and ferritin heavy chain subunit, from the bumblebee Bombus ignitus

Transferrin and ferritin are iron-binding proteins involved in transport and storage of iron as part of iron metabolism. Here, we describe the cDNA cloning and characterization of transferrin (Bi-Tf) and the ferritin heavy chain subunit (Bi-FerHCH), from the bumblebee Bombus ignitus. Bi-Tf cDNA spans 2340 bp and encodes a protein of 706 amino acids and Bi-FerHCH cDNA spans 1393 bp and encodes a protein of 217 amino acids. Comparative analysis revealed that Bi-Tf appears to have residues comprising iron-binding sites in the N-terminal lobe, and Bi-FerHCH contains a 5'UTR iron-responsive element and seven conserved amino acid residues associated with a ferroxidase center. The Bi-Tf and Bi-FerHCH cDNAs were expressed as 79 kDa and 27 kDa polypeptides, respectively, in baculovirus-infected insect Sf9 cells. Northern blot analysis revealed that Bi-Tf exhibits fat body-specific expression and Bi-FerHCH shows ubiquitous expression. The expression profiles of the Bi-Tf and Bi-FerHCH in the fat body of B. ignitus worker bees revealed that Bi-Tf and Bi-FerHCH are differentially induced in a time-dependent manner in a single insect by wounding, bacterial challenge, and iron overload.

Downregulation of ultraspiracle gene expression delays pupal development in honeybees

Ecdysteroids regulate many aspects of insect physiology after binding to a heterodimer composed of the nuclear hormone receptor proteins ecdysone receptor (EcR) and ultraspiracle (Usp). Several lines of evidence have suggested that the latter also plays important roles in mediating the action of juvenile hormone (JH) and, thus, integrates signaling by the two morphogenetic hormones. By using an RNAi approach, we show here that Usp participates in the mechanism that regulates the progression of pupal development in Apis mellifera, as indicated by the observed pupal developmental delay in usp knocked-down bees. Knock-down experiments also suggest that the expression of regulatory genes such as ftz transcription factor 1 (ftz-f1) and juvenile hormone esterase (jhe) depend on Usp. Vitellogenin (vg), the gene coding the main yolk protein in honeybees, does not seem to be under Usp regulation, thus suggesting that the previously observed induction of vg expression by JH during the last stages of pupal development is mediated by yet unknown transcription factor complexes.

Insect transferrin functions as an antioxidant protein in a beetle larva

In insects transferrin is known as an iron transporter, an antibiotic agent, a vitellogenin, and a juvenile hormone regulated protein. Here, a novel functional role for insect transferrin as an antioxidant protein is demonstrated. Stressors, such as heat shock, fungal challenge, and H(2)O(2) exposure, cause upregulation of the white-spotted flower chafer Protaetia brevitarsis (Coleoptera: Scarabaeidae) transferrin (PbTf) mRNA in the fat body and increases PbTf protein levels in the hemolymph. RNA interference (RNAi) treated PbTf reduction causes increased iron and H(2)O(2) levels in the hemolymph and results in induction of apoptotic cell death in the fat body during exposure to stress. The observed effects of PbTf RNAi suggest that PbTf inhibits stress-induced apoptosis by diminishing the Fenton reaction via the binding of iron, thus supporting an antioxidant role for PbTf in stress responses.

Genome-wide analysis reveals differences in brain gene expression patterns associated with caste and reproductive status in honey bees (Apis mellifera)

A key characteristic of eusocial species is reproductive division of labour. Honey bee colonies typically have a single reproductive queen and thousands of sterile workers. Adult queens differ dramatically from workers in anatomy, physiology, behaviour and lifespan. Young female workers can activate their ovaries and initiate egg laying; these 'reproductive' workers differ from sterile workers in anatomy, physiology, and behaviour. These differences, however, are on a much smaller scale than those observed between the queen and worker castes. Here, we use microarrays to monitor expression patterns of several thousand genes in the brains of same-aged virgin queens, sterile workers, and reproductive workers. We found large differences in expression between queens and both worker groups (~2000 genes), and much smaller differences between sterile and reproductive workers (221 genes). The expression patterns of these 221 genes in reproductive workers are more queen-like, and may represent a core group of genes associated with reproductive physiology. Furthermore, queens and reproductive workers preferentially up-regulate genes associated with the nurse bee behavioural state, which supports the hypothesis of an evolutionary link between worker division of labour and molecular pathways related to reproduction. Finally, several functional groups of genes associated with longevity in other species are significantly up-regulated in queens. Identifying the genes that underlie the differences between queens, sterile workers, and reproductive workers will allow us to begin to characterize the molecular mechanisms underlying the evolution of social behaviour and large-scale remodelling of gene networks associated with polyphenisms.

Genes of the antioxidant system of the honey bee: annotation and phylogeny

Antioxidant enzymes perform a variety of vital functions including the reduction of life-shortening oxidative damage. We used the honey bee genome sequence to identify the major components of the honey bee antioxidant system. A comparative analysis of honey bee with Drosophila melanogaster and Anopheles gambiae shows that although the basic components of the antioxidant system are conserved, there are important species differences in the number of paralogs. These include the duplication of thioredoxin reductase and the expansion of the thioredoxin family in fly; lack of expansion of the Theta, Delta and Omega GST classes in bee and no expansion of the Sigma class in dipteran species. The differential expansion of antioxidant gene families among honey bees and dipteran species might reflect the marked differences in life history and ecological niches between social and solitary species.

Transferrin inhibits stress-induced apoptosis in a beetle

Transferrin in insects is known as an iron transporter, an antibiotic agent, a vitellogenin, and a juvenile hormone-regulated protein. We show here a novel functional role for insect transferrin. Stresses, such as iron overload, bacterial or fungal challenge, cold or heat shock, wounding, and H2O2 or paraquat exposure, cause upregulation of the beetle Apriona germari transferrin (AgTf) gene in the fat body and epidermis, and they cause increased AgTf protein levels. RNA interference (RNAi)-mediated AgTf reduction results in rapid induction of apoptotic cell death in the fat body during exposure to heat stress. The observed effect of AgTf RNAi indicates that AgTf inhibits heat stress-induced apoptotic cell death, suggesting a functional role for AgTf in defense and stress responses in the beetle.

Solenopsis invicta transferrin: cDNA cloning, gene architecture, and up-regulation in response to Beauveria bassiana infection

Transferrin genes from several insects have been shown to be induced in response to bacterial or fungal infection. We were interested to know whether transferrin genes in the red imported fire ant, Solenopsis invicta, are similarly induced by microbial challenge. Hence, the cDNA and structure of a gene exhibiting significant homology to insect transferrins were elucidated for S. invicta. The cDNA was comprised of 2417 nucleotides, excluding the poly(A) tail, with a large open reading frame of 2106 nucleotides. The predicted translation product of the S. invicta tranferrin (SiTf) gene was a 702 amino acid polypeptide with an estimated molecular mass of 77.3 kDa and a pI value of 5.66, characteristics consistent with transferrin proteins. Comparative analysis of genomic and cDNA sequences revealed that the SiTf gene was comprised of 8 exons. Quantitative real-time PCR was used to examine the expression of SiTf. Expression of SiTf was induced in worker ants exposed to Beauveria bassiana conidia. Autoclave-killed conidia did not elicit a SiTf induction response from worker ants. Genes, like SiTf, responding to microbe attack or infection may provide a unique approach to assist in the discovery of microbial control organisms for the target insect pest.

Evolution of the transferrin family: Conservation of residues associated with iron and anion binding

The transferrin family spans both vertebrates and invertebrates. It includes serum transferrin, ovotransferrin, lactoferrin, melanotransferrin, inhibitor of carbonic anhydrase, saxiphilin, the major yolk protein in sea urchins, the crayfish protein, pacifastin, and a protein from green algae. Most (but not all) contain two domains of around 340 residues, thought to have evolved from an ancient duplication event. For serum transferrin, ovotransferrin and lactoferrin each of the duplicated lobes binds one atom of Fe (III) and one carbonate anion. With a few notable exceptions each iron atom is coordinated to four conserved amino acid residues: an aspartic acid, two tyrosines, and a histidine, while anion binding is associated with an arginine and a threonine in close proximity. These six residues in each lobe were examined for their evolutionary conservation in the homologous N- and C-lobes of 82 complete transferrin sequences from 61 different species. Of the ligands in the N-lobe, the histidine ligand shows the most variability in sequence. Also, of note, four of the twelve insect transferrins have glutamic acid substituted for aspartic acid in the N-lobe (as seen in the bacterial ferric binding proteins). In addition, there is a wide spread substitution of lysine for the anion binding arginine in the N-lobe in many organisms including all of the fish, the sea squirt and many of the unusual family members i.e., saxiphilin and the green alga protein. It is hoped that this short analysis will provide the impetus to establish the true function of some of the TF family members that clearly lack the ability to bind iron in one or both lobes and additionally clarify the evolutionary history of this important family of proteins.

Susceptibility of Rickettsia monacensis and Rickettsia peacockii to Cecropin A, Ceratotoxin A, and Lysozyme

Ticks host obligate intracellular bacteria that range from benign symbiotes to virulent human pathogens. The effects on those bacteria of antimicrobial peptides (AMPs) involved in arthropod innate immunity to microbial infections are largely unknown. We evaluated effects of AMPs and a c-type lysozyme on host cell-free suspensions of the tick symbiotes Rickettsia monacensis and Rickettsia peacockii with stain-based infectivity and viability assays. Cecropin A at a concentration of 8 muM: had a lethal effect on both rickettsiae while ceratotoxin A was approximately 20-fold less effective. Toxicity of both AMPs was synergized by lysozyme, an enzyme expressed by ticks. Lactoferrin, a transferrin, had no effect on R. monacensis at up to 110 microM. The rickettsiae were less sensitive to the AMPs than is typical of bacteria that grow extracellularly. Our assays may be useful in the study of AMP activity against other obligate intracellular bacteria.

Apis mellifera ultraspiracle: cDNA sequence and rapid up-regulation by juvenile hormone

Two hormones, 20-hydroxyecdysone (20E) and juvenile hormone (JH) are key regulators of insect development including the differentiation of the alternative caste phenotypes of social insects. In addition, JH plays a different role in adult honey bees, acting as a 'behavioural pacemaker'. The functional receptor for 20E is a heterodimer consisting of the ecdysone receptor and ultraspiracle (USP) whereas the identity of the JH receptor remains unknown. We have cloned and sequenced a cDNA encoding Apis mellifera ultraspiracle (AMUSP) and examined its responses to JH. A rapid, but transient up-regulation of the AMUSP messenger is observed in the fat bodies of both queens and workers. AMusp appears to be a single copy gene that produces two transcripts ( approximately 4 and approximately 5 kb) that are differentially expressed in the animal's body. The predicted AMUSP protein shows greater sequence similarity to its orthologues from the vertebrate-crab-tick-locust group than to the dipteran-lepidopteran group. These characteristics and the rapid up-regulation by JH suggest that some of the USP functions in the honey bee may depend on ligand binding.