Terminally differentiating Drosophila spermatids during the caspase-dependent vital cellular process of "individualization", where spermatids extrude their bulk cytoplasmic content into a waste bag (marked by the individualization complex; yellow/orange) to yield highly compact mature sperm cells. The krebs cycle components A-Sβ (green), is expressed on the surface (rather than in the matrix) of mitochondria, where it binds to and activates a Ub ligase complex required for caspase activation.
A Drosophila testis is shown with elongated spermatids during the removal of their bulk cytoplasm into the "waste bag" (red buldges), a process called "individualization". Soti (green), an inhibitor of a ubiquitin ligase complex required for caspase activation in this process, is expressed in a gradient from the tails (bottom) to the nuclear heads (top, blue) of the sperm cells. Consequently, caspase activation (activated effector caspase, red) occurs in an inverse graded fashion.
Drosophila spermatids are shown during an advance stage of the morphological process of "individualization". The apoptosis-like process of spermatid individualization- which separates the connections between developing spermatids- removes indeed organelles and excess cytoplasm, thereby promoting major changes of the cytoarchitecture. This process requires cell death proteins including apoptotic effector caspases (activated effector caspase is visualized by green staining). The tails of the individualizing spermatids are labled with an antibody for polyglycylated axonemal tubulin (blue staining). The expelled cytoplasm and organelles are collected into a membrane-enclosed structure known as the "cystic bulge" or "waste bag" (marked by the red filament staining of the individualization complex).
Florentin and Arama reveal that differences in the expression levels and execution efficiencies of caspases determine whether or not cells die in response to apoptotic stimuli. Wing imaginal discs from irradiated Drosophila are stained for active caspases (yellow), a reporter cleaved by caspases (blue), fragmented DNA (red), and apoptotic corpses (green).
The cover shows Drosophila spermatids in the process of removing their bulk cytoplasm. The expelled cytoplasm is collected into a "waste bag" (marked by the red filament staining) by an apoptosis-like process that requires caspase activity (green).