Development of Drosophila as a metazoan model to study inorganic polyphosphate biology

Inorganic polyphosphate (polyP), a linear polymer of orthophosphate residues, is found in all living organisms. While the biological and molecular functions of polyP have been studied in prokaryotes and unicellular eukaryotes, in metazoans it has often been referred to as a molecular fossil. Although certain functions of polyP, e.g. in blood clotting, have been uncovered in humans, a genetically tractable model system has not been developed to systematically study polyP function in metazoans. To explore Drosophila as a model to study polyP, we first developed methods to quantify polyP in flies and then analysed polyP levels in various tissues during different developmental stages. Interestingly, we found that the levels of polyP increase before pupal formation and significantly drop during metamorphosis. To check the in-situ localization of polyP, we used polyP binding domain of bacterial protein, namely PPBD to detect endogenous polyP in fly tissues. We report the presence of polyP in cytoplasm and enrichment in the nucleolus in most tissue types. Interestingly, during oogenesis, we found polyP is enriched in early stage egg chambers but get depleted in later stages suggesting that polyP may play a crucial role during ovariole development. Finally, we found polyP to be enriched in fly hemocytes and showed that polyP promotes hemolymph clotting suggesting that polyP function between flies and mammals is conserved. These observations strongly suggest that combining powerful Drosophila genetic and biochemical tools can accelerate the discovery of unknown biological functions of polyP in metazoans. ### Competing Interest Statement The authors have declared no competing interest.