JUVENILE-HORMONE PREVENTS THE ONSET OF PROGRAMMED CELL-DEATH IN THE PROTHORACIC GLANDS OF MANDUCA-SEXTA

During normal pupal-adult development, programmed cell death of the pr othoracic gland of Manduca sexta proceeds via apoptosis. By employing the DNA laddering technique, the earliest sign of DNA fragmentation in the cells comprising the gland occurred on Day 5 of pupal-adult devel opment and DNA fragmentation peaked 1 day later. Since juvenile hormon e (JH) is known to prevent adult development and since prothoracic gla nd degeneration occurs during the initial stages of adult development, we wished to determine the possible role of JH in prothoracic gland m aintenance. JH was injected into pupae and the glands analyzed by DNA laddering and in situ TUNEL labeling. The administration of JH prevent ed apoptosis of the prothoracic gland even 11 days after JH injection into young pupae. The prothoracic glands remained intact and their abi lity to synthesize ecdysteroids was maintained at a fairly active leve l as ascertained by radioimmunoassay after in vitro incubation. The co ntrol glands had degenerated by this time and were almost devoid of ec dysteroidogenesis capability. Ultrastructural analysis confirmed that JH-treated prothoracic gland cells were rescued from the apoptotic seq uence, i.e., nuclear condensation, cytoplasmic budding, and cell fragm entation. They exhibited a preserved smooth endoplasmic reticulum and intercellular channel system typical of active prothoracic gland cells . The composite data suggest that JH can both maintain and stimulate t he prothoracic gland. Therefore, during normal pupal-adult metamorphos is the absence of JH is prerequisite for both the initiation and compl etion of prothoracic gland degeneration. (C) 1998 Academic Press.