AKH BIOSYNTHESIS - TRANSCRIPTIONAL AND TRANSLATIONAL CONTROL OF 2 CO-LOCALIZED PROHORMONES

The neurosecretory cells of the locust corpora cardiaca (CC) express t wo co-localised transcripts which are translated into the two preproho rmones required in adipokinetic hormone I (AKH I) and AKH II biosynthe sis. At different stages of postembryonic development, the relative am ounts of the two transcripts (AKH I mRNA and AKH II mRNA) change in pa rallel with the relative rates of synthesis of proAKH I and proAKH II. Differential regulation of transcript expression, however, cannot acc ount 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 duri ng postembryonic development and is required to produce the observed d evelopmental 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 deve lopmentally changing pattern of peptide expression. We suggest that re gulation of neuropeptide ratios indicates that signalling functions ca n be attributed to the precise configuration of peptide cocktails.