Metabolic analysis of developmental progression in Drosophila

The growth and development of all animals involves transitions between different physiological states. The key developmental transition of critical weight (CW) in the fruit fly Drosophila melanogaster dramatically changes the growing larva’s response to nutrient restriction (NR). Developmental progression is arrested by NR before CW whereas it proceeds without delay when NR occurs after CW. It is known that the time of onset of CW and other developmental transitions are regulated by the steroid hormone ecdysone but questions remain concerning the nature of the physiological changes at CW and how they might confer NR-resistant developmental progression. To begin to answer these questions, I have analysed how the larval metabolome changes when nutrition is altered either side of the CW transition. The larval metabolome was recorded via nuclear magnetic resonance (NMR) spectroscopy and fitting reference spectra to recorded peaks enabled identification of the metabolites. Absolute metabolite concentrations could then be back-calculated from these spectra using the volume determination with two standards (VDTS) technique (Ragan, et al. 2013), which was further adapted to measure metabolite concentrations from the volume released from homogenisation of solid whole larval and adult samples. Through use of these techniques, I found that progression past CW correlates with the ability of fed and NR larvae to sustain a substantial increase in the concentration of tyrosine. An interesting interplay between tyrosine and a possible storage form of the metabolite: o-phosophotyrosine (OPT), suggests a process regulating the conversion between the two that may indirectly affect the biosynthesis of ecdysone. Dietary and genetic manipulations have been undertaken to draw a molecular mechanism for how varying tyrosine levels affected by CW attainment can effect time to pupariation (larval maturation). These results highlight how the field of NMR-metabolomics can be used to direct subsequent experiments to address biological questions.