Modes of cell death in the pupal perivisceral fat body tissue of the silkworm Bombyx mori L.

Cell death is a scheduled event during animal development and tissue turnover. Here, we affirm the presence of two major pathways of programmed cell death (PCD), viz. apoptotic and autophagic cell death, in the disintegrated pupal perivisceral (PV) fat body during pupal-adult metamorphosis. The acridine orange (a vital stain for apoptosis) staining pattern and DNA fragmentation assay have revealed the exact day (6th day of the pupal stage) of disintegration in the PV fat body as represented by chromatin condensation and DNA laddering. Electron microscopy and scanning electron microscopy have demonstrated the presence of cytoplasmic budding and giant autophagic vacuoles and the low numbers of mitochondria, all of which are attributes of autophagic cell death. Immunoblot analysis of proteosomal subunits 20S and 26S has established the involvement of proteolytic activity during PCD of PV tissue. Lysosomal participation during the PCD of PV tissues has been confirmed by the elevated level of the marker enzyme, acid phosphatase, which is distinct on day 6 of the pupal period. The results of the present study have thus ascertained the co-existence of both autophagic and apoptotic cell death in PV fat body tissue.