Identification, characterization and expression analysis of Anopheles stephensi double peroxidase

BmPxt1 mediated immune response by regulating PGE2 in silkworm, Bombyx mori

Prostaglandins (PGs) mediates the immune response of insects to multiple stimuli. Mammalian cyclooxygenase (COXs) is a key enzyme in the synthesis of PGs, and peroxinectin (Pxt) may have similar functions in some sequenced insect genomes. As a representative of Lepidoptera, the silkworm also contains PGs, but its synthetic pathway is not clear. We cloned a full-length cDNA encoding a Pxt, designated as BmPxt1, from silkworm. Sequence alignment analysis showed that the protein encoded by BmPxt1 has a conserved domain similar to Pxts, and its catalytic site is shared with the Pxt of Manduca sexta, which also produces PGs. The expression of BmPxt1 gene was the highest in the hemocytes and was induced by Nuclear Polyhedrosis Virus (NPV) challenge in the detected tissues. Moreover, we found that dsPxt1 treatment deficiency down-regulated BmPxt1 transcript levels and efficiently inhibiting hemocyte-spreading and nodule formation in silkworm. Hemocyte-spreading, nodule formation, phenoloxidase (PO) and AMP genes (attacin, defencin and moricin) were also inhibited by aspirin, a COX inhibitor. Treatment by PGE2 but not arachidonic acid (AA) rescued the immunosuppression; PGs concentrations was also inhibited by aspirin. PGE2, but not AA, treatment rescued the PGs concentrations. The COX inhibitor, aspirin, impaired the innate immune response including nodulation, encapsulation, and melanization in silkworm, while PGE2, but not arachidonic acid (AA), partially reversed these effects of aspirin. Recombinant BmsPxt1 significantly induced PO activation in larvae hemolymph, PGs concentrations and encapsulation of agarose beads. Injection of recombinant BmsPxt1 into larvae resulted in increased transcript levels of AMP genes. Our results confirmed that BmPxt1 was involved in the synthesis of PGs in the innate immune response of silkworm larvae, and provided new information for the role of BmsPxt1 secreted by silkworm in activating PO and antimicrobial peptides.

Double peroxidase and histone acetyltransferase AgTip60 maintain innate immune memory in primed mosquitoes

Immune priming in Anopheles gambiae is mediated by the systemic release of a hemocyte differentiation factor (HDF), a complex of lipoxin A₄ bound to Evokin, a lipid carrier. HDF increases the proportion of circulating granulocytes and enhances mosquito cellular immunity. Here, we show that Evokin is present in hemocytes and fat-body cells, and messenger RNA (mRNA) expression increases significantly after immune priming. The double peroxidase (DBLOX) enzyme, present in insects but not in vertebrates, is essential for HDF synthesis. DBLOX is highly expressed in oenocytes in the fat-body tissue, and these cells increase in number in primed mosquitoes. We provide direct evidence that the histone acetyltransferase AgTip60 (AGAP001539) is also essential for a sustained increase in oenocyte numbers, HDF synthesis, and immune priming. We propose that oenocytes may function as a population of cells that are reprogrammed, and orchestrate and maintain a broad, systemic, and long-lasting state of enhanced immune surveillance in primed mosquitoes.

Heme-Peroxidase 2, a Peroxinectin-Like Gene, Regulates Bacterial Homeostasis in Anopheles stephensi Midgut

The dynamic nature of mosquito gut microbiome is associated with different stages of development and feeding behaviors. Therefore, mosquito gut harbors a wide range of endogenous microbes that promote numerous life processes such as, nutrition, reproduction and immunity. In addition, gut microbiota also play an important role in the regulation of Plasmodium (malaria parasite) development. Thus, understanding the mechanism of microbial homeostasis in mosquito gut might be one of the strategies to manipulate malaria parasite development. In the present study, we characterized a 692 amino acids long secreted midgut heme-peroxidase 2 (AsHPX2) in Anopheles stephensi, the major Indian malaria vector. The presence of putative integrin binding motifs, LDV (Leu-Asp-Val), indicated its peroxinectin-like nature. Our phylogenetic analysis revealed that AsHPX2 is a Culicinae lineage-specific gene. RNA interference (RNAi)-mediated silencing of AsHPX2 gene significantly enhanced the growth of midgut bacteria in sugar-fed mosquitoes against sham-treated controls. Interestingly, blood-feeding drastically reduced AsHPX2 gene expression and enhanced the growth of midgut bacteria. These results revealed a negative correlation between the expression of AsHPX2 gene and gut bacterial growth. We proposed that AsHPX2, being a mosquito-specific gene, might serve as a "potent target" to manipulate midgut microbiota and vector competence.