Programmed cell death occurring in individually cultured midline lineages. (A,B) Frames from time-lapse recordings (real time is indicated) of two developing midline clones (see Additional files 1 and 2 for the corresponding movies). In both clones one out of three cells disintegrates into smaller particles within a short period of time (arrows). The cell in (A) moves apart from its siblings before undergoing apoptosis. Migration over such distances in neural cell cultures is normally only performed by glial cells. (C,D) Midline clones in which apoptosis of one cell is indicated by TUNEL staining (arrow). Cell sizes correspond to 5 to 8 μm.