Biomedical subjects

Xavier Nirmala

Publications and source records attributed to Xavier Nirmala.

4 recordsLinked to original sources

PubMed2006

Functional characterization of the promoter of the vitellogenin gene, AsVg1, of the malaria vector, Anopheles stephensi.

Some genetic strategies for controlling transmission of mosquito-borne diseases call for the introgression of antipathogen effector genes into vector populations. Endogenous mosquito promoter and other cis-acting DNA sequences are needed to direct the expression of the effector molecules to maximize their efficacy. Vitellogenin (Vg)-encoding gene control sequences are candidates for driving tissue-, stage- and sex-specific expression of exogenous genes. One of the Anopheles stephensi Vg genes, AsVg1, was cloned and a full-length cDNA, as well as 850 base pairs adjacent to the 5'-end, were sequenced and characterized. Expression of AsVg1 is restricted to the fat body tissues of blood-fed females, and the amino acid sequence of the conceptual translation product is >85% identical to those of other anopheline Vgs. These characteristics support the conclusion that AsVg1 is a Vg-encoding gene. Functional analyses of the AsVg1 putative cis-regulatory sequences were performed using transgenic mosquitoes. The results showed that DNA fragments encompassing the 850 base pairs immediately adjacent to the 5'-end of the gene and the 3'-end untranslated region are sufficient to direct sex-, stage- and tissue-specific expression of a reporter gene. These data indicate that the AsVg1 promoter is a good candidate for controlling the expression of anti-pathogen effector molecules in this malaria vector mosquito.

Animals↗

PubMed2006

Structure and expression of the lipophorin-encoding gene of the malaria vector, Anopheles gambiae.

Lipophorin is the major hemolymph protein responsible for lipid transport among tissues of insects. This protein may be a lipid source for the development and reproduction of human malaria parasites in mosquitoes, and therefore could be a target to disrupt malaria parasite development in the vector. The lipophorin of Anopheles gambiae was purified by KBr gradient ultracentrifugation and showed variation in density from 1.111 to 1.143 g/ml during development. The amount and density of lipophorin increase in blood-fed females, indicating an adaptation of vitellogenic mosquitoes to an elevated rate of lipid transport to the developing eggs. The A. gambiae lipophorin gene is composed of eight exons and transcribes an mRNA that is 10,516 nucleotides in length. The predicted initial translation product is a preproapoliphorin consisting of 3332 amino acids, which is processed by proteolysis to generate two mature apolipophorins: apolipophorin-I (Mr = 280,000) and apolipophorin-II (Mr = 81,000). The gene is expressed in the fat body tissues throughout development. An elevated transcriptional activity of the lipophorin gene during vitellogenesis is consistent with the presence of putative cis-regulatory elements (GATA and ecdysone responsive elements) in its 3'-end flanking DNA sequence.

Amino Acid Sequence↗

PubMed2005

Structurally unique recombinant Kazal-type proteinase inhibitor retains activity when terminally extended and glycosylated.

Recombinant derivatives of the Kazal-type serine proteinase inhibitor GmSPI2 (36 amino acid residues), which is a component of insect silk, were prepared in the expression vector Pichia pastoris. The rhSPI2 had a C-terminal hexahistidine tag attached to the GmSPI2 sequence, rtSPI2 was extended with GluAlaAla at the N-terminus, and rfSPI2 included this N-terminal extension and a C-terminal tail of 22 residues (myc epitope and hexahistidine). A portion of the secreted rfSI2 was O-glycosylated with a trimannosyl or hexamannosyl. The native inhibitor was active slightly on trypsin and highly on subtilisin and proteinase K. The extended C-terminus in rhSPI2 and rfSPI2 enhanced activity on the two latter enzymes and rendered rfSPI2 active on elastase and pronase, but abolished the inhibition of trypsin. The glycosylation of rfSPI2 reduced its inhibitory activity to a level comparable with the native inhibitor. The rtSPI2 with tripeptide extension at the N-terminus and no C-terminal modification was clearly less active than the native inhibitor. None of the tested compounds inhibited alpha-chymotrypsin and the non-serine proteinases.

Amino Acid Sequence↗

PubMed2003

Engineering Plasmodium-refractory phenotypes in mosquitoes.

A remarkable number of effector mechanisms have been developed for interfering with malaria parasite development in mosquitoes. These effector mechanisms affect different aspects of parasite biology and therefore could be targeted synergistically to reduce the probability of emergence of parasite resistance to any one mechanism. The use of these mechanisms will depend on how efficiently and safely they can be introduced into existing mosquito populations.

Animals↗