The splicing factor 9G8 regulates the expression of NADPH-producing enzyme genes in Drosophila

Abstract

Excess nutrients are stored as triglycerides, mostly as lipid droplets found in adipose tissue. Previous studies have characterized a group of splicing factors called serine/arginine rich (SR) proteins that function to identify intron/exon borders in regulating metabolic homeostasis in the Drosophila fat body. Decreasing the function of one SR protein, 9G8, causes an increase in triglyceride storage; however, the full complement of genes regulated by 9G8 to control metabolism is unknown. To address this question, we performed RNA sequencing on Drosophila fat bodies with 9G8 levels reduced by RNAi. Differential expression and differential exon usage analyses revealed several genes involved in the immune response, xenobiotic biology, protein translation, sleep, and lipid and carbohydrate metabolism whose expression or splicing is altered in 9G8-RNAi fat bodies. One gene that was both downregulated and had altered splicing in 9G8-RNAi fat bodies was Zwischenferment (Zw), the Drosophila homolog of human glucose 6-phosphate dehydrogenase (G6PD). G6PD regulates flux of glucose 6-phosphate (G6P) into the pentose phosphate pathway, which generates NADPH, a coenzyme for lipid synthesis. Interestingly, the other NADPH-producing enzyme genes in Drosophila (phosphogluconate dehydrogenase, isocitrate dehydrogenase and malic enzyme) were also decreased in 9G8-RNAi flies. Together, these findings suggest that 9G8 regulates several classes of genes and may regulate NADPH-producing enzyme genes to maintain metabolic homeostasis.