Post-transcriptional regulation of gene expression during the programmed death of insect skeletal muscle.

While considerable attention has focused on the role of specific proteins in mediating programmed cell death, few studies have examined the possible involvement of post-transcriptional regulation of mRNAs associated with this developmental process. We have examined developmental changes in transcript stability and translatability using protein extracts generated from the intersegmental muscles (ISM) of the moth Manduca sexta as a cell-free model system to examine three genes that are representative of the patterns of expression observed in condemned ISMs: repressed (actin), induced (polyubiquitin) and constitutively expressed (ubiquitin-fusion 80; ubf80). In addition, we have used luciferase mRNA as a generic reporter transcript to determine if there are sequence-specific controls of mRNA function related to programmed cell death. Among the three Manduca transcripts, polyubiquitin displayed the shortest half-life (t1/2) in all ISM extracts tested. The stability and translatability of all mRNAs were most affected in extracts from muscle cells from day 17 animals, just prior to the commitment of the muscles to die. Transfer of the 3' untranslated regions from the Manduca transcripts to luciferase mRNA did not appreciably change the stability or translatability of this test transcript. These data suggest that there may be global removal of cellular transcripts just prior to death to allow newly expressed mRNAs to rapidly accumulate to high levels. Such changes in message abundance, translatability and stability may facilitate the efficient activation of death (and perhaps other differentiation programs) in some developmental systems.