Biomedical subjects

N Harizanova

Publications and source records attributed to N Harizanova.

3 recordsLinked to original sources

PubMed2005

Aedes aegypti transferrin. Gene structure, expression pattern, and regulation.

Mosquitoes and all other insects so far examined have an abundant haemolymph transferrin (Tsf). The exact function of these proteins has not been determined, but they may be involved in iron transport, in oogenesis and in innate immune defence against parasites and pathogens. The Tsf gene of Aedes aegypti has been cloned and sequenced. It contains a single small intron, which contrasts it to vertebrate Tsf genes that contain up to sixteen introns. The promoter region of the gene is rich in putative NF-kappaB binding sites, which is consistent with the postulated role of Tsf in insect innate immunity. Tsf message levels are very low in embryos and early larvae, but high in late larvae, pupae and adults. Western blotting experiments revealed high levels of Tsf protein in pupae and adults. Late larvae and ovaries of blood-fed mosquitoes have little intact protein, but two prominent proteolytic degradation products. These may represent biologically active peptides, as has been shown for other organisms. Tsf message is down-regulated by inorganic iron in the diet or environment, but up-regulated by a blood meal in the adult female. The up-regulation following a blood meal may, in part, be due to the decrease in juvenile hormone (JH) that is known to follow blood feeding. Treatment of blood-fed females with methoprene, an analogue of JH, resulted in decrease of the Tsf message.

Aedes↗

PubMed1999

Iron availability dramatically alters the distribution of ferritin subunit messages in Drosophila melanogaster.

Insect ferritins have subunits homologous to the heavy and light chains of vertebrate ferritins. Cloning and sequence of the heavy chain homologue (HCH) of Drosophila melanogaster ferritin subunit have been reported earlier. When Northern blots of D. melanogaster RNA were probed with a cDNA for this HCH, three bands were observed. It was shown that these represented at least four classes of mRNA of various lengths. The polymorphism results from alternative splicing of an intron in the 5' untranslated region (UTR) that contains the iron-responsive element (IRE) and from two alternative polyadenylation sites in the 3' UTR. This has also been reported by others [Lind, M. I., Ekengren, S., Melefors, O. & Söderhäll, K. (1998) FEBS Lett. 436, 476-482]. By hybridizing Northern blots with specific probes, it has been shown that the relative proportions of the messages vary with the life stage and especially with iron supplementation of the diet. Iron significantly increases the amount of ferritin HCH messages and dramatically shifts the balance toward those messages that lack an IRE and/or have a short 3' UTR. In the larvae this change takes place in the gut, but not in the fat body. We speculate that this dramatic shift in message distribution may result from an effect of iron on the rate of transcription or message degradation, or from an effect on the splicing process itself. Synthesis of ferritin HCH subunit mRNAs that lack an IRE may be important under conditions of iron overload.

5' Untranslated Regions↗

PubMed1999

Drosophila melanogaster transferrin. Cloning, deduced protein sequence, expression during the life cycle, gene localization and up-regulation on bacterial infection.

Drosophila melanogaster transferrin cDNA was cloned from an ovarian cDNA library by using a PCR fragment amplified by two primers designed from other dipteran transferrin sequences. The clone (2035 bp) encodes a protein of 641 amino acids containing a signal peptide of 29 amino acids. Like other insect transferrins, Drosophila transferrin appears to have a functional iron-binding site only in the N-terminal lobe. The C-terminal lobe lacks iron-binding residues found in other transferrins, and has large deletions which make it much smaller than functional C-terminal lobes in other transferrins. In-situ hybridization using a digoxigenin labeled transferrin cDNA probe revealed that the gene is located at position 17B1-2 on the X chromosome. Northern blot analysis showed that transferrin mRNA was present in the larval, pupal and adult stages, but was not detectable in the embryo. Iron supplementation of the diet resulted in lower levels of transferrin mRNA. When adult flies were inoculated with bacteria (Escherichia coli), transferrin mRNA synthesis was markedly increased relative to controls.

Amino Acid Sequence↗