Daphne Q.-D. Pham

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.

Repression of Manduca sexta ferritin synthesis by IRP1/IRE interaction.

Mammalian ferritin subunit synthesis is controlled at the translational level by the iron regulatory protein 1 (IRP1)/iron responsive element (IRE) interaction. Insect haemolymph ferritin subunit messages have an IRE in the 5′‐untranslated region (UTR). We have shown that recombinant M. sexta IRP1 represses the in vitro translation of both the heavy and light chain ferritin subunits from this species without altering transcription. Deletion of either the 5′‐UTR or the IRE from the mRNA abolishes IRP1 repression. Our studies indicated that the translational control of ferritin synthesis by IRP/IRE interaction could occur in insects in a manner similar to that of mammals. To our knowledge, this is the first report of the control of insect ferritin synthesis by IRP1/IRE interaction. Furthermore, this is the first indication that the synthesis of a secreted ferritin subunit can also be controlled in this manner.

Impact of multiple prenatal risk factors on newborn iron status at delivery.

Background: Maternal anemia and several complications of pregnancy can affect fetal iron acquisition. Aim: Because it is unknown whether the effects of demographic and maternal risk factors (RF) are summative, we examined cord iron status in newborns with multiple RF for acquiring iron deficiency. Methods: Cord blood indices from healthy control newborns with and without RF for newborn or infant iron deficiency were studied. Results: Newborns with greater RF had poorer erythrocyte and storage iron status. Poorest status was seen if mothers with comorbid obesity and diabetes delivered large-for-gestation newborns. Findings highlight the importance of identifying RF.

The ferritin light-chain homologue promoter in Aedes aegypti

Promoters that direct the expression of antipathogenic molecules to primary sites of pathogenic invasions provide a means to interfere with these invasions. Thus, they have the potential to be used in mosquito control. However, exogenous elements are known to lower the fitness of most insects, and given the ability of insects to evolve rapidly, all currently known promoters could be rendered useless. As transgenic mosquitoes may be a major component in the fight against mosquito‐borne diseases, the identification of new mosquito promoters is needed. The promoter of the Aedes aegypti ferritin light‐chain homologue (LCH) gene, a gene whose expression is induced in gut tissues during blood feeding has been identified and mapped. Transfection data indicate that the ferritin LCH promoter is a strong promoter. DNase I footprinting data and Transfac analyses suggest that the ferritin LCH promoter contains putative GATA, E2F, NIT2, TATA and DPE sites. These data together provide the first detailed map of a known ferritin LCH gene.

Identification and mapping of the promoter for the gene encoding the ferritin heavy-chain homologue of the yellow fever mosquito Aedes aegypti.

Mosquitoes are responsible for the transmission of numerous human diseases. The recent development of transgenic mosquitoes provides a new tool to examine molecular interactions between insect vectors and the pathogens they transmit. One focus in generating transgenic mosquito lies on expressing anti-pathogenic proteins at primary sites of pathogenic invasions, specifically the mosquito gut. Promoters that direct the expression of anti-pathogenic proteins in the mosquito gut are thus sought after because they may provide ways to hinder pathogenic development in the mosquito. Here, we report the identification and mapping of a strong promoter from the Aedes aegypti ferritin heavy-chain homologue (HCH) gene. All known insect ferritin HCH genes are expressed in the gut and inducible by an iron overload. Our transfection assays and DNase I footprinting analyses show that the mosquito ferritin HCH-gene contains regulatory elements both upstream and downstream of the transcriptional start site. The promoter of this gene contains a CF2 site, two GATA-binding sites, an E2F site, a TATA-box, an AP-1 site and a C/EBP binding site.

Regulation of the ferritin heavy-chain homologue gene in the yellow fever mosquito, Aedes aegypti

In the yellow fever mosquito Aedes aegypti, the ferritin heavy‐chain homologue (HCH) gene is induced by blood feeding. This suggests that ferritin may serve as a cytotoxic protector against the oxidative challenge of the blood meal and may be essential for the survival of the insect. In this study, various cis‐acting elements for the gene were identified and mapped. Transfection assays showed that the strength and activity of a subset of these elements are orientation‐dependent. The shift observed for the ferritin HCH cis‐acting elements is unique among known ferritin genes. DNase I footprinting data together with Transfac analyses identified a number of putative sites known for their involvement in developmental and cell proliferation processes.

Ribonucleotide reductase subunits from the yellow fever mosquito, Aedes aegypti: cloning and expression

Ribonucleotide reductase catalyses the de novo synthesis of deoxyribonucleotides. Class I reductases use an iron center to generate a tyrosyl free radical that can initiate formation of the deoxyribonucleotide. These reductases are alpha 2 beta 2 holoenzymes, and the subunits are denoted as R1 and R2. R1 contains the allosteric binding site and the active site, whereas R2 contains a binuclear iron center that initiates formation of the tyrosyl radical. We have cloned and sequenced the cDNAs encoding the R1 and R2 subunit in the yellow fever mosquito, Aedes aegypti. The messages for these proteins are increased in response to blood-feeding.