Mutations in the Drosophila melanogaster gene pyruvate kinase interfere with larval development
Pyruvate kinase (Pyk) is a rate-limiting enzyme that catalyzes the final metabolic reaction in glycolysis. The importance of this enzyme, however, extends far beyond ATP production, as Pyk is also known to regulate tissue growth, cell proliferation, and development. Studies of this enzyme in Drosophila melanogaster, however, are complicated by the fact the fly genome encodes six Pyk paralogs and the function of these individual genes remain poorly defined. To address this issue, we used a phylogenetic approach to demonstrate that the gene Pyk encodes the enzyme most similar to the mammalian Pyk orthologs while the other five Drosophila Pyk have significantly diverged from the canonical enzyme. Consistent with this observation, metabolomic studies of two different Pyk mutant backgrounds revealed that larvae lacking Pyk exhibit a severe block in glycolysis, with a buildup of glycolytic intermediates upstream of pyruvate. However, our analysis also unexpectantly reveals that steady state pyruvate levels are unchanged in Pyk mutants, indicating that larval metabolism maintains pyruvate pool size despite severe metabolic limitations. Consistent with our metabolomics findings, a complementary RNAseq analysis revealed that genes involved in lipid metabolism and peptidase activity are elevated in Pyk mutants, again indicating that loss of this glycolytic enzyme induces compensatory changes in other aspects of metabolism. Overall, our study provides both insight towards understanding how Drosophila larval metabolism adapts to disruption of glycolytic metabolism and immediate clinical relevance considering that Pyk deficiency is the most common congenital enzymatic defect in humans. Overall design: RNA-seq of Pyk 23/+ heterozygous controls versus Pyk 23/31 CRISPR mutants, three whole-fly biological replicates