Abstract
Insect hormones and microRNAs regulate lipid metabolism, but the mechanisms are not fully elucidated. Here, we found that cotton bollworm larvae feeding on Arabidopsis thaliana (AT) leaves had a lower triacylglycerol (TAG) level and more delayed development than individuals feeding on artificial diet (AD). Association analysis of small RNA and mRNA revealed that the level of miR-2055, a microRNA related to lipid metabolism, was significantly higher in larvae feeding on AT. Dual-luciferase reporter assays demonstrated miR-2055 binding to 3' UTR of fatty acid synthase (FAS) mRNA to suppress its expression. Elevating the level of miR-2055 in larvae by agomir injection decreased FAS mRNA and protein levels, which resulted in reduction of free fatty acid (FFA) and TAG in fat body. Interestingly, in vitro assays illustrated that juvenile hormone (JH) increased miR-2055 accumulation in a dosage-dependent manner, whereas knockdown of Methoprene tolerant (Met) or Kruppel homologue 1 (Kr-h1) decreased the miR-2055 level. This implied that JH induces the expression of miR-2055 via a Met-Kr-h1 signal. These findings demonstrate that JH and miRNA cooperate to modulate lipid synthesis, which provides new insights into the regulatory mechanisms of metabolism in insects.
Highlights
Lipids are essential energy sources in animals and play important roles in individual growth and development
Insulin acts as an activator of protein kinase B (PKB), which can repress the activity of Bmm by phosphorylating transcription factor Orkhead box subgroup O (FOXO) [6]
Insect hormones and miRNAs are major factors involved in modulating lipid metabolism and development, but knowledge of the cross-talking between them is still limited
Summary
Lipids are essential energy sources in animals and play important roles in individual growth and development. In Drosophila melanogaster, TAG is hydrolysed into free fatty acids (FFAs) and glycerol under the control of two different lipases, Brummer (Bmm) and hormone-sensitive lipase (Hsl) [2,3], and FFAs can serve as substances in β-oxidation and other biochemical reactions. The regulation of TAG catabolism is strictly supervised by the insulin and adipokinetic hormone (AKH) pathways. During the process of TAG synthesis, FFAs, one of the major substances, can be obtained from diets or be synthesized de novo by two key enzymes, acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS). The transcription of these two enzymes is controlled by the transcription factor sterol-regulatory element binding protein (SREBP), which can be activated by insulin [1]
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