Defining the contribution of select neuropeptides and their receptors in regulating sesquiterpenoid biosynthesis by Drosophilamelanogaster ring gland/corpus allatum through RNAi analysis

The larval ring gland and adult corpus allatum (CA) of Drosophilamelanogaster produce at least three sesquiterpenoid products: methyl farnesoate (MF), juvenile hormone III (JHIII), and JHIII bisepoxide (JHB₃). Our understanding of neuropeptide regulation of sesquiterpenoid biosynthesis in D. melanogaster has been hampered by uncertainty over the biosynthetic pathway and the sites of action of regulators. As an approach to defining the neuropeptide regulators, we have used invivo gene-specific silencing (RNAi). D. melanogaster strains containing an inducible UAS-RNAi construct made to either PheGlyLeu-NH₂–allatostatin (FGLa/AST) and its cognate receptors Dar-1 and Dar-2 or PISCF–allatostatin (PISCF/AST) or its cognate receptors Drostar-1 or Drostar-2 were expressed invivo. MF, JHIII and JHB₃ production was measured in ring glands of 3rd instars or corpora allata (CA) of adult females using the radiochemical assay. Reduction in FGLa/AST and Dar-1 or Dar-2 mRNA levels had no effect on MF, JHIII, or JHB₃ production in larvae or adults. Inhibition of Drostar-1 expression resulted in a significant decrease in MF and JHB₃ production in 3rd instars with little effect on JHIII biosynthesis. In contrast, inhibition of Drostar-1 in adult females led to a significant increase in MF and JHIII production. Inhibition of Drostar-2 also reduced MF biosynthesis in 3rd instars. In adults, inhibition of Drostar-2 led to a significant increase in MF and JHIII production but showed no effect on JHB₃. PISCF/AST had no effect on sesquiterpenoid biosynthesis when incubated with 3rd instar ring glands but was stimulatory when incubated with adult glands. Inhibition of short neuropeptide F (sNPF) expression by RNAi or application of sNPF to ring glands had no effect on MF, JHIII, or JHB3 biosynthesis in larvae or adults. Reduction in the neuropeptide Y receptor (NepYr) or neuropeptide F receptor (NPF-R) inhibited JHIII and JHB₃ production in 3rd instars but only reduction in NepYr resulted in JHB₃ reduction in adults.