TUNEL-antibody double-labeling method for Drosophila embryos

The terminal deoxynucleotide transferase (TdT)-mediated dUTP nick-end labeling (TUNEL) method for monitoring targeted cell ablation is based on the in situ labeling of DNA fragmentation sites in nuclei of intact fixed cells. Unlike other methods of detecting dying cells, the use of fixed material allows antigen expression to be monitored at the same time that apoptosis is confirmed in the targeted cells. Double-labeling of Drosophila embryos using the TUNEL reaction and fluorescently tagged antibodies can be adapted to the selected antigen. For some antigens, it is preferable that the TUNEL reaction be performed first, whereas for others, the TUNEL reaction should follow antigen detection. This may be because some antigens may not survive the 37°C incubation or the conditions of the reaction. Similarly, increased fixation times yield better results for some antigens, but not for others. This protocol describes a TUNEL reaction adapted for use on Drosophila embryos in conjunction with fluorescently labeled antibodies.