Gfat1 and Gfat2 encode functionally equivalent enzymes in Drosophila melanogaster: a molecular, genetic, and evolutionary analysis

The hexosamine biosynthesis pathway (HBP) diverts 2-5% of glucose from glycolysis, ultimately producing uridine diphosphate N-acetylglucosamine (UDP-GlcNAc), an important substrate in protein glycosylation. This pathway is of particular importance in Drosophila melanogaster because chitin, the primary component of insect cuticle, is composed of N-acetylglucosamine polymers. I report that the rate-limiting enzymes of the HBP, GFAT1 and GFAT2 (glutamine:fructose-6-phosphate aminotransferase), are functionally equivalent by genetic rescue using cDNA transgenes of both genes. I also report that neither transgenically upregulating the enzymes of the HBP, nor those of the hexosamine signalling pathway (HexSP), extends the lifespan of D. melanogaster. Evolutionary analyses using fluorescence in situ hybridization in six species of Drosophila support a model that would place the Gfat1 relocalization event from euchromatin to heterochromatin after the melanogaster group diverged from the rest of Drosophila.