Rapid Induction by a Blood Meal of a Carboxypeptidase Gene in the Gut of the Mosquito Anopheles gambiae

Abstract

A search for genes induced rapidly (<3 h) after a blood meal in the gut of the human malaria vector Anopheles gambiae led to the identification of a carboxypeptidase gene ( AgCP). We report the sequence of the 1302 nt AgCP transcribed sequence, 710 nt of upstream and 585 nt of downstream DNA. The AgCP open reading frame is 60.4% identical at the nucleotide level to a blackfly, Simulium vittatum, carboxypeptidase gene. The transcriptional start site of AgCP was determined by primer extension. Expression of AgCP mRNA is detectable in the guts of pupae and sugar-fed adult female mosquitoes and is induced (∼10-fold) within 3 h of a blood meal. By 24 h after a blood meal, mRNA abundance returns to a level close to that present before a blood meal. Whole-mount in situ hybridization shows that AgCP mRNA expression is restricted to most or all cells of the posterior midgut. Expression of the AgCP and trypsin genes were compared and shown to differ in two fundamental ways: (1) the peak of AgCP expression after a blood meal occurs approximately 20 h before that of trypsin; and (2) induction of the AgCP gene is independent of the composition of the ingested meal whereas trypsin induction requires the presence of protein. The potential use of the AgCP promoter for driving the expression of genes that hinder the development of parasites in the mosquito gut is discussed.