J. Terashima et al., Programmed cell death triggered by insect steroid hormone, 20-hydroxyecdysone, in the anterior silk gland of the silkworm, Bombyx mori, DEV GENES E, 210(11), 2000, pp. 545-558
Silk gland is a larval specific tissue of lepidopteran insects and begins t
o degenerate shortly before pupation. Programmed cell death (PCD) of the an
terior silk gland of Bombyx mori last instar larvae was studied in vivo and
in vitro, focusing on the effects of 20-hydroxyecdysone (20E). The glands
began to exhibit signs of PCD in vivo 2, days after gut purge and completed
PCD by 48 h. In vitro, 20E prematurely induced PCD, and its completion too
k 144 h (6 days). An oligonucleosomal ladder pattern was observed in DNA ex
tracted at the end of PCD. Caspase 3 inhibitor inhibited attainment of full
PCD, but it did not block chromatin condensation as revealed by acridine o
range staining. a-Amanitin inhibited the PCD induced by 20E in vitro if add
ed to the culture in the first 8 h. Similarly, cycloheximide and emetine co
mpletely blocked PCD when applied in the first 18 h of culture with 20E. Th
ese results indicate that 20E-stimulated transcription and protein synthesi
s for PCD are completed in 8 h and 18 h, respectively. Nevertheless, withdr
awal of 20E from the medium at different times showed that 20E must be pres
ent in vitro for 42 h to elicit full PCD. Current results indicate that the
effects of 20E on the progression of PCD are mediated by two distinct prec
esses - one through nuclear hormone receptors, and the other independent fr
om de novo gene expression.