Insulin-like peptides in the mosquito Anopheles stephensi: identification and expression in response to diet and infection with Plasmodium falciparum.

Insulin-like peptides (ILPs) regulate a multitude of biological processes, including metabolism and immunity to infection, and share similar structural motifs across widely divergent taxa. Insulin/insulin-like growth factor signaling (IIS) pathway elements are similarly conserved. We have shown that IIS regulates reproduction, innate immunity, and lifespan in female Anopheles stephensi, a major mosquito vector of human malaria. To further explore IIS regulation of these processes, we identified genes encoding five ILPs in this species and characterized their expression in tissues. Antisera to ILP homologs in Anopheles gambiae were used to identify cellular sources in An. stephensi females by immunocytochemistry. We analyzed tissue-specific ILP transcript expression in young and older females, in response to different feeding regimens, and in response to infection with Plasmodiumfalciparum with quantitative reverse transcriptase-PCR assays. While some ILP transcript changes were evident in older females and in response to blood feeding, significant changes were particularly notable in response to hormonal concentrations of ingested human insulin and to P. falciparum infection. These changes suggest that ILP secretion and action may be similarly responsive in Plasmodium-infected females and potentially alter metabolism and innate immunity.