PROGRAMMED CELL-DEATH SPECIFICALLY ELIMINATES ONE PART OF A LOCUST PLEUROAXILLARY MUSCLE AFTER THE IMAGINAL MOLT

In the hemimetabolous insect Locusta migratoria, fundamental restructu ring occurs at the transition from flightless nymph to Right-capable a dult. This transition involves all components of the Right circuit, wh ich is present but not used for flight in nymphs. The meso- and metath oracic pleuroaxillary muscles, M85 and M114 respectively, constitute o ne component of this circuit, In the adult locust, these are flight-st eering muscles, but their function in the nymph is as yet unknown. Our study reveals that adult and nymphal metathoracic pleuroaxillary musc les M114 differ profoundly. The nymphal muscle contains the distinct p art M114c in addition to parts M114a and M114b characteristic of the a dult. The contractions of M114c are slow and long-lasting, correspondi ng to its long sarcomeres and slow form of ATPase, and contrast with t he adult muscle parts M114a and M114b in all of these features. We dem onstrate a hormone-dependent degeneration of M114c after the adult mou lt. This degeneration can be blocked by actinomycin D and cycloheximid e. It may thus be termed genetically programmed cell death, triggered after the adult moult and, as demonstrated here, functioning via the A TP-dependent ubiquitin pathway. Given the defined onset of degeneratio n after the adult moult, it is possible that M114c may fulfil a specif ic function in nymphs, during or shortly after moulting.