Summary

The neurosecretory cells of the locust corpora cardiaca (CC) express two co-localised transcripts which are translated into the two preprohormones required in adipokinetic hormone I (AKH I) and AKH II biosynthesis. At different stages of postembryonic development, the relative amounts of the two transcripts (AKH I mRNA and AKH II mRNA) change in parallel with the relative rates of synthesis of proAKH I and proAKH II. Differential regulation of transcript expression, however, cannot account for the changes in neuropeptide ratios seen during postembryonic development. Comparison of in vivo and in vitro translation shows that protein synthesis in vivo is biased towards the translation of AKH I mRNA by a factor of about 2.6. This factor appears to be constant during postembryonic development and is required to produce the observed developmental changes in neuropeptide ratios. Both transcriptional and translational mechanisms are therefore necessary to alter neuropeptide ratios in the CC. The mechanisms we describe can account for the developmentally changing pattern of peptide expression. We suggest that regulation of neuropeptide ratios indicates that signalling functions can be attributed to the precise configuration of peptide cocktails.