Abstract:  【Aim】 To detect the cell dissociation, autophagy and apoptosis in the prothoracic gland of the silkworm, Bombyx mori during metamorphosis, and to compare tissue demise in the prothoracic gland with that in the fat body, so as to uncover the similarities and differences of tissue remodeling during the larval-pupal metamorphosis. 【Methods】 With the prothoracic gland and fat body tissues of B. mori at the 5th instar, wandering, prepupal and pupal stages as the test materials, the cell dissociation in the prothoracic gland and fat body of B. mori was observed under light microscopy. The autophagy and apoptosis were observed after Lyso-Tracker and TUNEL staining, respectively, under fluorescence confocal microscopy. The expression profile of the autophagy marker gene Atg8 in the prothoracic gland was detected by qRT-PCR. The autophagosome in the prothoracic gland and fat body as well as the morphological changes of mitochondria in the prothoracic gland were observed under transmission electron microscopy. The Caspase3 activity was assayed using Capase3 enzyme assay kit. The expression profiles of Halloween genes Spo, Phm, Dib and Sad were detected by qRT-PCR. The ecdysone content in the prothoracic gland was detected by enzyme-immunoassay (EIA) aiming at furthermore determining the activity of the synthesis of ecdysone. 【Results】 During the transition from larva to pupa of B. mori, both the prothoracic gland and fat body began to undergo cell dissociation on the 1st day of pupation. Autophagy and apoptosis in the fat body began to appear at the wandering stage and day 1 of prepupa, respectively, and gradually increased. However, autophagy and apoptosis did not occur in the prothoracic gland until the 2nd day after pupation. In addition, the morphological changes of mitochondria and the transcription levels of Halloween genes were consistent with the activity of ecdysone synthesis in the prothoracic gland at the corresponding developmental stage of B. mori. 【Conclusion】 The time of tissue demise is different in different tissues of B. mori during metamorphosis. Cell dissociation appears on the 1st day after pupation in both the prothoracic gland and the fat body; however, autophagy and apoptosis in the prothoracic gland do not occur until the 2nd day after pupation, which may be related to its function in continuous synthesis of ecdysone. This study provides important scientific basis for the in-depth study of tissue demise during the larval-pupal metamorphosis in insects.

Key words: Bombyx mori, prothoracic gland, fat body, cell dissociation, apoptosis')">autophagy; apoptosis, programmed cell death