The transcription factor dFOXO controls the expression of insulin pathway genes and lipids content under heat stress in &lt;i&gt;Drosophila melanogaster&lt;/i&gt;

M A Eremina,N E Gruntenko,P N Menshanov,O D Shishkina

doi:10.18699/vj21.053

Abstract

The insulin/insulin-like growth factor signaling (IIS) pathway is one of the key elements in an organism’s response to unfavourable conditions. The deep homology of this pathway and its evolutionary conservative role in controlling the carbohydrate and lipid metabolism make it possible to use Drosophila melanogaster for studying its functioning. To identify the properties of interaction of two key IIS pathway components under heat stress in D. melanogaster (the forkhead box O transcription factor (dFOXO) and insulin-like peptide 6 (DILP6), which intermediates the dFOXO signal sent from the fat body to the insulin-producing cells of the brain where DILPs1–5 are synthesized), we analysed the expression of the genes dilp6, dfoxo and insulin-like receptor gene (dInR) in females of strains carrying the hypomorphic mutation dilp641 and hypofunctional mutation foxoBG01018. We found that neither mutation influenced dfoxo expression and its uprise under short-term heat stress, but both of them disrupted the stress response of the dilp6 and dInR genes. To reveal the role of identified disruptions in metabolism control and feeding behaviour, we analysed the effect of the dilp641 and foxoBG01018 mutations on total lipids content and capillary feeding intensity in imago under normal conditions and under short-term heat stress. Both mutations caused an increase in these parameters under normal conditions and prevented decrease in total lipids content following heat stress observed in the control strain. In mutants, feeding intensity was increased under normal conditions; and decreased following short-term heat stress in all studied strains for the first 24 h of observation, and in dilp641 strain, for 48 h. Thus, we may conclude that dFOXO takes part in regulating the IIS pathway response to heat stress as well as the changes in lipids content caused by heat stress, and this regulation is mediated by DILP6. At the same time, the feeding behaviour of imago might be controlled by dFOXO and DILP6 under normal conditions, but not under heat stress.

Highlights

Nowadays, as living beings often encounter unfavourable en vironmental conditions such as pollution and global warming, the study of deeply conservative mechanisms that contribute to adaptation is of current interest
This study aimed to analyse the expression of dfoxo and insulin-like receptor gene (dInR), dilp6 and dfoxo genes of three key components of the IIS pathway, which is involved in neuroendocrine stress reaction, in D. melanogaster strains carrying dilp6 41 и foxo BG01018 mutations under heat stress, and to evaluate the latter’s influence on feeding behaviour and total lipids content in these strains
To discover whether disruption of the feedback loop of the IIS pathway regulation affects its stress response, we studied the expression of three key genes of the pathway, dilp6, dfoxo and dInR, in D. melanogaster females carrying hypomorphic mutation dilp6 41 and hypofunctional mutation foxo BG01018 under normal conditions or heat stress (38 °С, 90 min)

Summary

Introduction

As living beings often encounter unfavourable en vironmental conditions such as pollution and global warming, the study of deeply conservative mechanisms that contribute to adaptation is of current interest. The ability to respond to stress in an integrated manner, which comprises behavioral, metabolic and molecular reactions, is key for survival and adaptation of animals includ ing insects (Koyama et al, 2020). It was proven that besides its role as crucial modulator of growth and metabolism, in insects, the IIS pathway is an essential component of the neuroendocrine stress reaction (Gruntenko, Rauschenbach, 2018; Lubawy et al, 2020). Due to the deep homology of this pathway in animals of different taxa including humans and flies, it is possible to use the latter as an object for investigating evolutionary-conservative mechanisms underlying molecu lar-genetic regulation of the IIS pathway, and carbohydrate and lipid metabolism it controls. In insects, carbohydrates and lipids serve as the main energy supply (Ar rese, Soulages, 2010). The processes of producing and storing energy undergo complex modulation by many inner factors including heritage, lifestyle, hormones, metabolites, as well as various outside influences (Mattila, Hietakangas, 2017)

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