RESUMO
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 dilp6 41and hypofunctional mutation foxo BG01018. We found that neither mutation inf luenced 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 identif ied disruptions in metabolism control and feeding behaviour, we analysed the effect of the dilp6 41 and foxo BG01018 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 f irst 24 h of observation, and in dilp6 41 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.
RESUMO
The insulin/insulin-like growth factor signaling pathway is involved in the regulation of the synthesis of insect gonadotropic hormones, juvenile (JH) and 20-hydroxyecdysone (20E). We carried out the immunohistochemical analysis of the insulin receptor (InR) expression in the corpus allatum (the JH-producing gland) and in the ovarian follicular cells (a site for the synthesis of 20E precursor, ecdysone) in the process of sexual maturation of D. melanogaster females and examined the influence of exogenous JH on the InR expression in these tissues. For the first time, it was demonstrated that InR was expressed in follicular cells and that its expression in corpus allatum and follicular cells of Drosophila females was stage-specific, i.e., the expression intensity in young females greatly exceeded that in mature individuals. We also found a negative feedback loop in the regulation of JH levels by the insulin signaling pathway in Drosophila adults: the experimental increase in the JH titers in young females dramatically reduced the InR expression intensity in corpus allatum and follicular cells.
