EdU (5-ethynyl-2'-deoxyuridine) labeling of Drosophila mitotic neuroblasts.

When examining mutants that affect cell fate as a result of altered asymmetric division patterns, it is important to determine whether cells are mitotically active. Chemical labeling of newly synthesized DNA (during S-phase) by incorporation of BrdU (5-bromo-2'-deoxyuridine) is informative because this thymidine analog can be used to pulse-label dividing cells and then chased to identify the progeny of dividing cells. Such pulse-chase experiments can provide additional insight by distinguishing actively dividing cells from those that might be arrested at a mitotic checkpoint. EdU (5-ethynyl-2'-deoxyuridine) is another thymidine analog that provides a more sensitive and practical alternative to BrdU. Incorporation of EdU is detected through its reaction with an azide dye that is small enough to penetrate tissues efficiently. Visualization of EdU is rapid and does not interfere with subsequent antibody staining. The use of EdU in labeling Drosophila mitotic neuroblasts is described here.