Transcriptomic analyses of Aedes aegypti cultured cells and ex vivo midguts in response to an excess or deficiency of heme: a quest for transcriptionally-regulated heme transporters

Heather Eggleston,Zach N Adelman

doi:10.1186/s12864-020-06981-5

Abstract

BackgroundAedes aegypti is the principle vector of many arboviruses, including dengue virus and Zika virus, which are transmitted when an infected female mosquito takes a blood meal in order to initiate vitellogenesis. During blood digestion, ~ 10 mM heme-iron is ingested into the midgut lumen. While heme acts as both a nutrient and signaling molecule during blood digestion, it can also be highly toxic if left unchaperoned. Both signaling by, and degradation of, heme are intracellular processes, occurring in the nucleus and cytoplasm, respectively. However, the precise mechanism of heme uptake into the midgut epithelium is not currently known.ResultsWe used next generation RNA sequencing with the goal to identify genes that code for membrane bound heme import protein(s) responsible for heme uptake into the midgut epithelium. Heme deprivation increased uptake of a heme fluorescent analog in cultured cells, while treatment of midguts with an excess of heme decreased uptake, confirming physiological changes were occurring in these heme-sensitive cells/tissues prior to sequencing. A list of candidate genes was assembled for each of the experimental sample sets, which included Aag2 and A20 cultured cells as well as midgut tissue, based on the results of a differential expression analysis, soft cluster analysis and number of predicted transmembrane domains. Lastly, the functions related to heme transport were examined through RNAi knockdown.ConclusionsDespite a large number of transmembrane domain containing genes differentially expressed in response to heme, very few were highly differentially expressed in any of the datasets examined. RNAi knockdown of a subset of candidates resulted in subtle changes in heme uptake, but minimal overall disruption to blood digestion/egg production. These results could indicate that heme import in Ae. aegypti may be controlled by a redundant system of multiple distinct transport proteins. Alternatively, heme membrane bound transport in Ae. aegypti could be regulated post-translationally.

Highlights

Aedes aegypti is the principle vector of many arboviruses, including dengue virus and Zika virus, which are transmitted when an infected female mosquito takes a blood meal in order to initiate vitellogenesis
Zinc Mesoporphyrin (ZnMP) visualization of heme import changes in response to heme overload or deficiency As no heme transport proteins have been identified in any dipteran, we sought to develop an assay to rapidly assess heme transport ability in mosquito cells
In this study, we examined the response of two Ae. aegypti cultured cell lines and midgut epithelial tissue to heme overload or deficiency conditions in order to identify novel genes involved in heme transport as no genes with heme transport capacity have been identified in this mosquito previously

Summary

Introduction

Aedes aegypti is the principle vector of many arboviruses, including dengue virus and Zika virus, which are transmitted when an infected female mosquito takes a blood meal in order to initiate vitellogenesis. While heme acts as both a nutrient and signaling molecule during blood digestion, it can be highly toxic if left unchaperoned. Both signaling by, and degradation of, heme are intracellular processes, occurring in the nucleus and cytoplasm, respectively. Two key sources of nutrients obtained from these proteins include amino acids and heme-iron. While heme acts as both a source of iron that is deposited into the developing eggs [11], it is a signaling molecule resulting in the activation of vitellogenesis through the activation of the steroid hormone 20-hydroxyecdysone by binding to and stabilizing the nuclear receptor E75 [12,13,14,15,16]

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