The Role of the Drosophila Anorexia (Anox) Gene in Insulin Signaling and Metamorphosis
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Following the discovery of Insulin, it took the rest of the twentieth century to understand how this hormone regulates intracellular metabolism; however, understanding how insulin induces its profound effects on blood-glucose homeostasis and metabolism has proved difficult. The understanding of molecular basis of insulin signaling pathway comes from research conducted on model organisms such as Drosophila melanogaster. As a holometabolous insect, Drosophila undergoes dramatic changes during metamorphosis, and many larval organs are destroyed or remodeled as the animal transforms from a larval to an adult. One organ that plays a crucial role in these transformations is the larval fat body. During larval life Drosophila goes through three stages called “instars.” During the 3rd instar the fly exits the food and prepares to enter the pupal stage. The animal does not feed during the pupa stage so in order to fuel metamorphosis it stores all its nutrients in the fat body during larval stages. The use of nutrients stored in the fat body is regulated by the insulin signaling pathway. The expression of a recently identified gene, Anorexia, in the central nervous system has been shown to regulate feeding behavior through the insulin signaling. In this study through quantitative PCR (qPCR), I have been able show the presence of significant Anorexia gene expression in the larval fat body of the wild type 3rd instar larvae. Anorexia RNAi flies were generated which inhibited expression of the gene in larval fat body or central nervous system by RNA interference. The feeding assay revealed the RNAi flies to have significantly less food uptake compared to the wild type. These findings suggest that the larval fat body expresses significant levels of Anox mRNA, leading to active insulin signaling regulation by Anox in the larval fat body to effect feeding activity and metabolism in Drosophila.
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