Department of Biological Sciences and Science and Technology Center for Light Microscope Imaging and Biotechnology, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, PA 15213, USA.
Programmed cell death plays an essential role during Drosophila embryonic development. A stereotypic series of cellular changes occur during apoptosis, most of which are initiated by a caspase cascade that is triggered by a trio of proteins, RPR, HID and GRIM. The final step in apoptosis is engulfment of the cell corpse. To monitor cell engulfment in vivo, we developed a fluorogenic beta-galactosidase substrate that is cleaved by an endogenous, lysosomal beta-galactosidase activity. The pattern of cell engulfment in wild-type embryos correlated well with the known pattern of apoptosis. Surprisingly, the pattern of cell engulfment persisted in apoptosis-deficient embryos. We provide evidence for a caspase-independent engulfment process that affects the majority of cells expected to die in developing Drosophila embryos.