Fig. 2. Macrophages of Drosophila PSR^FM1 embryos are competent to engulf apoptotic cells. Macrophages are marked with GFP in embryos that are srp-hemo-GAL-4, UAS-src-EGFP or srp-hemo-GAL-4, UAS-src-EGFP; dPSR^FM1 (lacking both maternal and zygotic dPSR). Embryos (8-10 hours) were fixed, and the red apoptotic nuclei were observed after staining with 10 µg/ml 7-aminoactinomycin D or TUNEL and visualized by confocal microscopy. (A) Wild-type macrophages (green) can be observed to contain engulfed TUNEL-labeled apoptotic cell nuclei (red). (B) Macrophages in homozygous dPSR^FM1 embryos also contain many apoptotic nuclei. (C) Engulfment was quantified as the mean number of phagocytosed apoptotic nuclei per macrophage (phagocytic index). The mean and standard error are shown. At least five macrophages from eight age-matched embryos per genotype were analyzed (total macrophages analyzed were 65 for wild type and 68 for dPSR^FM1). Homozygous dPSR^FM1 embryos show a slight increase in apoptotic cell engulfment by macrophages, possibly owing to increased cell death.