Ornithine decarboxylase deficiency critically impairs nitrogen metabolism and survival in Aedes aegypti mosquitoes

Abstract

Ornithine decarboxylase (ODC; EC 4.1.1.17) catalyzes the conversion of ornithine to putrescine, the rate‐limiting first step for de novo polyamine biosynthesis. Previously, we reported that genetic knockdown of xanthine dehydrogenase 1 (XDH1)—a gene encoding the enzyme involved in the last two steps of uric acid synthesis—causes an increase in ODC transcript levels in fat body of blood‐fed Aedes aegypti mosquitoes, suggesting a crosstalk at molecular level between XDH1 and ODC during nitrogen disposal. To further investigate the role of ODC in nitrogen metabolism, we conducted several biochemical and genetic analyses in sugar‐ and blood‐fed A. aegypti females. Distinct ODC gene and protein expression patterns were observed in mosquito tissues dissected during the first gonotrophic cycle. Both pharmacological and RNA interference‐mediated knockdown of ODC negatively impacted mosquito survival, disrupted nitrogen waste disposal, delayed oviposition onset, and decreased fecundity in vitellogenic blood‐fed females. A lag in the expression of two major digestive serine proteases, a reduction of blood meal digestion in the midgut, and a decrease in vitellogenin yolk protein uptake in ovarian follicles were observed by western blots in ODC‐deficient females. Moreover, genetic silencing of ODC showed a broad transcriptional modulation of genes encoding proteins involved in multiple metabolic pathways in mosquito fat body, midgut, and Malpighian tubules prior to and after blood feeding. All together, these data demonstrate that ODC plays an essential role in mosquito metabolism, and that ODC crosstalks with multiple genes and proteins to prevent deadly nitrogen perturbations in A. aegypti females.