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Inositol catabolism via myo-inositol oxygenase in Drosophila melanogaster



myo-Inositol is a six-carbon ring sugar that is important for many cellular processes in eukaryotes and some bacteria. It plays a role as a precursor of the membrane component phosphatidylinositol, in signal transduction pathways, and as an osmoregulator in response to environmental stress. myo-Inositol oxygenase (MIOX) catalyzes the conversion of myo-inositol to glucuronic acid in the first committed step of eukaryotic inositol catabolism. In human diabetics inositol homeostasis is often disturbed through mechanisms that are largely unknown. Depletion of myo-inositol is associated with diabetic complications (e.g. nephropathies, retinopathies, and diabetic cataracts). MIOX has been shown to be expressed in the kidneys and the extra-renal tissues where these complications occur. MIOX has not been annotated in the model organism Drosophila melanogaster, but the protein encoded by the D. melanogaster CG6910 gene has 54.6% identity to the Mus musculus MIOX protein. CG6910 is also highly similar to MIOX genes in a number of other organisms. D. melanogaster has an inositol catabolic pathway because wild-type strains can grow on defined media with inositol as the only carbon source. Establishing that CG6910 encodes MIOX allows for studies on D. melanogaster to have cross-species relevance to humans. The knock-down expression of CG6910 was explored using RNAi gene silencing. The ubiquitous Act5C-GAL4 driver was introduced into two independent CG6910 RNAi strains of D. melanogaster. These constructs should yield two independent variants of ubiquitous knock-down expression of CG6910. To determine if the knock-down expression of CG6910 altered inositol catabolism, these D. melanogaster were grown on defined media with either sucrose or inositol. Similar to flies on defined media without any sugar as a carbon/energy source, flies with the CG6910 RNAi and with the Act5C-GAL4 driver did not survive more than five days on the inositol defined media. This indicates that CG6910 encodes MIOX. Preliminary experiments of Western blot analyses show a decrease in MIOX expression in CG6910 RNAi flies with the Act5C-GAL4 driver. Other initial experiments include a biochemical assay demonstrating MIOX activity in D. melanogaster. These studies may contribute to understanding the role of inositol catabolism in fruit fly development and diabetes.


drosophila melanogaster, metabolism, rna interference