Juvenile Hormone Prevents the Onset of Programmed Cell Death in the Prothoracic Glands ofManduca sexta

Abstract

During normal pupal–adult development, programmed cell death of the prothoracic gland ofManduca sextaproceeds 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 development and DNA fragmentation peaked 1 day later. Since juvenile hormone (JH) is known to prevent adult development and since prothoracic gland degeneration occurs during the initial stages of adult development, we wished to determine the possible role of JH in prothoracic gland maintenance. JH was injected into pupae and the glands analyzed by DNA laddering andin situTUNEL labeling. The administration of JH prevented apoptosis of the prothoracic gland even 11 days after JH injection into young pupae. The prothoracic glands remained intact and their ability to synthesize ecdysteroids was maintained at a fairly active level as ascertained by radioimmunoassay afterin vitroincubation. The control glands had degenerated by this time and were almost devoid of ecdysteroidogenesis capability. Ultrastructural analysis confirmed that JH-treated prothoracic gland cells were rescued from the apoptotic sequence, i.e., nuclear condensation, cytoplasmic budding, and cell fragmentation. 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 the prothoracic gland. Therefore, during normal pupal–adult metamorphosis the absence of JH is prerequisite for both the initiation and completion of prothoracic gland degeneration.