Roles and regulation of autophagy and apoptosis in the remodelling of the lepidopteran midgut epithelium during metamorphosis.
We previously showed that autophagy and apoptosis occur in the removal of the lepidopteran larval midgut during metamorphosis. However, their roles in this context and the molecular pathways underlying their activation and regulation were only hypothesized. The results of the present study better clarify the timing of the activation of these two processes: autophagic and apoptotic genes are transcribed at the beginning of metamorphosis, but apoptosis intervenes after autophagy. To investigate the mechanisms that promote the activation of autophagy and apoptosis, we designed a set of experiments based on injections of 20-hydroxyecdysone (20E). Our data demonstrate that autophagy is induced at the end of the last larval stage by the 20E commitment peak, while the onset of apoptosis occurs concomitantly with the 20E metamorphic peak. By impairing autophagic flux, the midgut epithelium degenerated faster, and higher caspase activity was observed compared to controls, whereas inhibiting caspase activation caused a severe delay in epithelial degeneration. Our data demonstrate that autophagy plays a pro-survival function in the silkworm midgut during metamorphosis, while apoptosis is the major process that drives the demise of the epithelium. The evidence collected in this study seems to exclude the occurrence of autophagic cell death in this setting.
Department of Biotechnology and Life Sciences, University of Insubria, 21100 Varese, Italy.
Davide
D
Romanelli
Department of Biosciences, University of Milano, 20133 Milano, Italy.
Morena
M
Casartelli
CREA - Honey Bee and Silkworm Research Unit, Padua seat, 35143 Padova, Italy.
Silvia
S
Cappellozza
Department of Biotechnology and Life Sciences, University of Insubria, 21100 Varese, Italy.
Magda
M
de Eguileor
Department of Biotechnology and Life Sciences, University of Insubria, 21100 Varese, Italy.
Gianluca
G
Tettamanti
D000818:Animals; D017209:Apoptosis; D001343:Autophagy; D012831:Bombyx / Q000502:physiology*; D007413:Intestinal Mucosa / Q000502:physiology; D008675:Metamorphosis, Biological