Expression profile of the iron-binding proteins transferrin and ferritin heavy chain subunit in the bumblebee Bombus ignitus

A ferritin protein is involved in the development and reproduction of the whitefly, Bemisia tabaci

Ferritins are conserved iron-binding proteins that exist in most living organisms and play an essential role in the maintenance of cellular iron homeostasis. Although ferritin has been studied in many species, little is known about its role in the whitefly, Bemisia tabaci. In this study, we identified an iron-binding protein from B. tabaci and named it BtabFer1. The full-length cDNA of BtabFer1 is 1,043 bp and encodes a protein consisting of 224 amino acids with a deduced molecular weight of 25.26 kDa, and phylogenetic analysis shows that BtabFer1 is conserved among Hemiptera insects. The expression levels of BtabFer1 in different developmental stages and tissues were analyzed by real-time PCR, and results showed that BtabFer1 was ubiquitously expressed at all developmental stages and in all examined tissues. The RNAi-mediated knockdown of BtabFer1 caused a significant reduction in survival rate, egg production, and egg hatching rate of whiteflies. Knockdown of BtabFer1 also inhibited the transcription of genes in the juvenile hormone signal transduction pathway. Taken together, these results suggest that BtabFer1 plays a critical role in the development and reproduction of whiteflies. This study can broaden our understanding of ferritin in insect fecundity and development, as well as provide baseline data for future studies.

Laser capture microdissection to study Bacillus cereus iron homeostasis gene expression during Galleria mellonella in vivo gut colonization

Bacillus cereus is a Gram-positive opportunistic pathogen closely related to the entomopathogen, Bacillus thuringiensis, both of which are involved in intestinal infections. Iron is an essential micronutrient for full growth and virulence of pathogens during infection. However, little is known about iron homeostasis during gut infection. Therefore, we aimed to assess the expression of B. cereus genes related to bacterial iron homeostasis, virulence and oxidative stress. The hypothesis is that the expression of such genes would vary between early and later stage colonization in correlation to gut cell damage. To perform the study, a germ-free Galleria mellonella model was set up in order to adapt the use of Laser-capture microdissection (LCM), to select precise areas in the gut lumen from frozen whole larval cryo-sections. Analyses were performed from alive larvae and the expression of targeted genes was assessed byspecific pre-amplification of mRNA followed by quantitative PCR. Firstly, the results reinforce the reliability of LCM, despite a low amount of bacterial RNA recovered. Secondly, bacterial genes involved in iron homeostasis are expressed in the lumen at both 3 and 16 hours post force-feeding. Thirdly, iron gene expression is slightly modulated during gut infection, and lastly, the mRNA of G. mellonella encoding for ferritin and transferrin iron storage and transport are recovered too. Therefore, iron homeostasis should play a role in B. cereus gut colonization. Furthermore, we demonstrate for the first time the value of using LCM for specific in situ gene expression analysis of extracellular bacteria in a whole animal.

Upregulation of Transferrin and Major Royal Jelly Proteins in the Spermathecal Fluid of Mated Honeybee (Apis mellifera) Queens

Simple Summary

To understand the mechanisms underlying long-term storage and survival of sperm in honeybee Apis mellifera queens, previous studies have elucidated the components of honeybee spermathecal fluid. However, the expression profiles of transferrin (Tf) and major royal jelly proteins 1–9 (MRJPs 1–9) in the spermatheca and spermathecal fluid of mated honeybee queens have still not been characterized. In this study, we confirmed upregulation of Tf and MRJPs in the spermatheca and spermathecal fluid of mated honeybee queens by using RNA sequencing, reverse transcription-polymerase chain reaction, and Western blot analyses. The levels of Tf and antioxidant enzymes were elevated in the spermathecal fluid of the mated queens, paralleling the levels of reactive oxygen species, H₂O₂, and iron. The increased levels of MRJPs, especially MRJP1, MRJP4, and MRJP6, in the spermathecal fluid of mated queens may be responsible for energy provision during sperm storage in honeybee queens. Overall, our findings indicate that Tf and MRJPs are upregulated in the spermatheca and spermathecal fluid of mated honeybee queens, providing a novel insight into antioxidant defense and energy metabolism for stored sperm in honeybee queens.

Abstract

Sperm storage in the spermathecae of honeybee (Apis mellifera) queens is vital for reproduction of honeybees. However, the molecular mechanisms whereby queens store sperm in a viable state over prolonged periods in the spermatheca are not fully understood. Here, we conducted RNA sequencing analysis of the spermathecae in both virgin and mated A. mellifera queens 24 h after mating and observed that the genes encoding transferrin (Tf) and major royal jelly proteins (MRJPs) were differentially expressed in the spermathecae of mated queens. The concentrations of Tf and antioxidant proteins such as superoxide dismutase 1, catalase, and glutathione peroxidase as well as the levels of reactive oxygen species, H₂O₂, and iron were higher in the spermathecal fluid of the mated queens than in virgin queens. Tf upregulation is likely to perform a protective role against the Fenton reaction occurring between iron and H₂O₂ in the antioxidant pathway in the mated queen’s spermathecal fluid. Furthermore, MRJPs—especially MRJP1, MRJP4, and MRJP6—were upregulated in the mated queen’s spermathecal fluid, indicating that they may serve as antimicrobial and antioxidant agents as well as an energy source for stored sperm in the spermathecal fluid of honeybee queens. Together, our findings show that Tf and MRJPs are upregulated in the spermatheca and spermathecal fluid of mated honeybee queens.

RNAi-mediated silencing of ferritin genes in the brown planthopper Nilaparvata lugens affects survival, growth and female fecundity

BACKGROUND

The brown planthopper (BPH), Nilaparvata lugens, is the most destructive rice insect pest. To exploit potential target genes for applications in transgenic rice to control this sap-sucking insect pest, three ferritin genes were functionally characterized in this study.

RESULTS

In this study, three ferritin genes, that is, ferritin 1 Heavy Chain (NlFer1), ferritin 2 Light Chain (NlFer2) and soma ferritin (Nlsoma-Fer), were identified from BPH. Tissue-specific analyses showed that all three genes were highly expressed in the gut. Although double-stranded RNA injection-mediated RNA inference (RNAi) of Nlsoma-Fer expression resulted in only < 14% mortality in BPH, knockdown of NlFer1 or NlFer2 led to retarded growth and 100% mortality in young nymphs, and downregulation of NlFer1 and NlFer2 in newly emerged female adults caused undeveloped ovaries and severely inhibited oocyte growth, resulting in extremely low fecundity and a zero hatching rate. Knockdown of NlFer1 and NlFer2 caused similar phenotypes in BPH, indicating that they function together, as in many other animals. The results demonstrated that NlFer1 and NlFer2 were essential for BPH development and reproduction. BPHs showed high sensitivity to both dsNlFer1 and dsNlFer2, and injection of only 0.625 ng dsNlFer1 per BPH resulted in 100% mortality. Additionally, the effectiveness of feeding dsNlFer1 and dsNlFer2 to BPH nymphs was further proven.

CONCLUSION

NlFer1 and NlFer2 are essential for BPH development and reproduction, and the insect is highly sensitive to their depletion, suggesting that the two gut-highly-expressed genes are promising candidates for application in RNAi-based control of this destructive pest.

Characterization of a Vitellogenin Receptor in the Bumblebee, Bombus lantschouensis (Hymenoptera, Apidae)

The vitellogenin receptor (VgR) belongs to the low-density lipoprotein receptor (LDLR) family, responsible for mediating the endocytosis of vitellogenin (Vg) into the ovaries to promote ovarian growth and oviposition. Here, we cloned and measured VgR gene expression characteristics in the bumblebee Bombus lantschouensis. RNA interference was used to validate VgR function. The results showed that the full length of the BLVgR cDNA was 5519 bp, which included a 5280 bp open reading frame encoding 1759 amino acids (AAs). Sequence alignment revealed that the protein contained 12 LDLa, 5 EGF, 2 EGF-CA and 10 LY domains. Phylogenetic analysis showed that BLVgR and the VgR of Bombus terrestris clustered together and the tree of bumblebees (Bombus) appeared as one clade next to honeybees (Apis). Transcript expression analysis showed that BLVgR was expressed in all tested tissues and showed the highest abundance in the ovaries. BLVgR expression was present in all developmental stages. However, the expression level in larvae was extremely low. In addition, the expression of BLVgR was significantly upregulated after egg laying in both workers and queens. In new emerging workers injected with 5 µg of VgR dsRNA, the expression level of BLVgR was 4-fold lower than that in the GFP dsRNA-injected group after 72 h. Furthermore, BLVgR silencing significantly reduced the number of eggs laid (3.67 ± 1.96 eggs) and delayed the first egg-laying time (16.31 ± 2.07 days) in worker microcolonies when compared to dsGFP (37.31 ± 4.09 eggs, 8.15 ± 0.22 days) and DEPC-treated water injected controls (16.42 ± 2.24 eggs, 10.00 ± 0.37 days). In conclusion, the BLVgR gene and its reproductive function were explored in the bumblebee B. lantschouensis. This gene plays an important role in egg laying time and egg number.

Iron and Ferritin Deposition in the Ovarian Tissues of the Yellow Fever Mosquito (Diptera: Culicidae)

Dengue, yellow fever, and Zika are viruses transmitted by yellow fever mosquito, Aedes aegypti [Linnaeus (Diptera: Culicidae)], to thousands of people each year. Mosquitoes transmit these viruses while consuming a blood meal that is required for oogenesis. Iron, an essential nutrient from the blood meal, is required for egg development. Mosquitoes receive a high iron load in the meal; although iron can be toxic, these animals have developed mechanisms for dealing with this load. Our previous research has shown iron from the blood meal is absorbed in the gut and transported by ferritin, the main iron transport and storage protein, to the ovaries. We now report the distribution of iron and ferritin in ovarian tissues before blood feeding and 24 and 72 h post-blood meal. Ovarian iron is observed in specific locations. Timing post-blood feeding influences the location and distribution of the ferritin heavy-chain homolog, light-chain homolog 1, and light-chain homolog 2 in ovaries. Understanding iron deposition in ovarian tissues is important to the potential use of interference in iron metabolism as a vector control strategy for reducing mosquito fecundity, decreasing mosquito populations, and thereby reducing transmission rates of vector-borne diseases.

Silkworm ferritin 1 heavy chain homolog is involved in defense against bacterial infection through regulation of haemolymph iron homeostasis

Iron functions as a nutrient and a potential toxin in all organisms. It plays a key role in the interaction between microbes and their hosts as well. Microbial infection disrupts iron homeostasis in the host; meanwhile the host endeavors to keep the homeostasis through iron transport and storage. Transferrins and ferritins are the major iron-binding proteins that affect iron distribution in insects. In this study, we investigated a possible involvement of Bombyx mori ferritin 1 (BmFer1) heavy chain homolog in the defense against bacterial infection in the silkworm larvae. The BmFer1 mRNA abundance was up-regulated in hemocytes, but not in fat body, after Pseudomonas aeruginosa or Staphylococcus aureus infection. The infection resulted in elevated iron levels in the hemolymph. Injection of recombinant BmFer1 protein into hemocoel reduced the plasma iron level after infection, limited the bacterial growth in the hemolymph, and resulted in a lower mortality caused by infection. Our study indicated that B. mori ferritin-1 may restrict iron access of the invading bacteria to block their growth as a defense strategy.

The genomes of two key bumblebee species with primitive eusocial organization

Background

The shift from solitary to social behavior is one of the major evolutionary transitions. Primitively eusocial bumblebees are uniquely placed to illuminate the evolution of highly eusocial insect societies. Bumblebees are also invaluable natural and agricultural pollinators, and there is widespread concern over recent population declines in some species. High-quality genomic data will inform key aspects of bumblebee biology, including susceptibility to implicated population viability threats.

Results

We report the high quality draft genome sequences of Bombus terrestris and Bombus impatiens, two ecologically dominant bumblebees and widely utilized study species. Comparing these new genomes to those of the highly eusocial honeybee Apis mellifera and other Hymenoptera, we identify deeply conserved similarities, as well as novelties key to the biology of these organisms. Some honeybee genome features thought to underpin advanced eusociality are also present in bumblebees, indicating an earlier evolution in the bee lineage. Xenobiotic detoxification and immune genes are similarly depauperate in bumblebees and honeybees, and multiple categories of genes linked to social organization, including development and behavior, show high conservation. Key differences identified include a bias in bumblebee chemoreception towards gustation from olfaction, and striking differences in microRNAs, potentially responsible for gene regulation underlying social and other traits.

Conclusions

These two bumblebee genomes provide a foundation for post-genomic research on these key pollinators and insect societies. Overall, gene repertoires suggest that the route to advanced eusociality in bees was mediated by many small changes in many genes and processes, and not by notable expansion or depauperation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13059-015-0623-3) 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.

The immune response of the small interfering RNA pathway in the defense against bee viruses

Most bee viruses are RNA viruses belonging to two major families of Dicistroviridae and Iflaviridae. During viral infection, virus-derived double stranded RNAs activate a major host innate immune pathway, namely the small interfering RNAs pathway (siRNA pathway), which degrades the viral RNA or the viral genome. This results in 21-22 nucleotide-long virus-derived siRNAs (vsiRNAs). Recent studies showed that vsiRNAs, matching to viruses from the family of Dicistroviridae and Iflaviridae, were generated in infected bees. Moreover, higher virus titers in honeybees also resulted in higher amounts of vsiRNAs, demonstrating that the siRNA response is proportional to the intensity of viral infection. Intriguingly, non-specific dsRNA could also trigger an immune response, leading to the restriction of the viral infection, however this mechanism is still unclear. Other findings demonstrated that bees can be protected through introducing virus specific-dsRNA to activate the siRNA response against the target virus. The latter is highlighting a new strategy to tackle bee viruses.

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.

Insect ferritins: Typical or atypical?

Insects transmit millions of cases of disease each year, and cost millions of dollars in agricultural losses. The control of insect-borne diseases is vital for numerous developing countries, and the management of agricultural insect pests is a very serious business for developed countries. Control methods should target insect-specific traits in order to avoid non-target effects, especially in mammals. Since insect cells have had a billion years of evolutionary divergence from those of vertebrates, they differ in many ways that might be promising for the insect control field-especially, in iron metabolism because current studies have indicated that significant differences exist between insect and mammalian systems. Insect iron metabolism differs from that of vertebrates in the following respects. Insect ferritins have a heavier mass than mammalian ferritins. Unlike their mammalian counterparts, the insect ferritin subunits are often glycosylated and are synthesized with a signal peptide. The crystal structure of insect ferritin also shows a tetrahedral symmetry consisting of 12 heavy chain and 12 light chain subunits in contrast to that of mammalian ferritin that exhibits an octahedral symmetry made of 24 heavy chain and 24 light chain subunits. Insect ferritins associate primarily with the vacuolar system and serve as iron transporters-quite the opposite of the mammalian ferritins, which are mainly cytoplasmic and serve as iron storage proteins. This review will discuss these differences.