Apoptotic cell death is essential for development and tissue homeostasis. 
Failure to clear apoptotic cells can ultimately cause inflammation and 
autoimmunity. Apoptosis has primarily been studied by staining of fixed tissue 
sections, and a clear understanding of the behavior of apoptotic cells in living 
tissue has been elusive. Here, we use a newly developed technique to track 
apoptotic cells in real time as they emerge and are cleared from the zebrafish 
brain. We find that apoptotic cells are remarkably motile, frequently migrating 
several cell diameters to the periphery of living tissues. F-actin remodeling 
occurs in surrounding cells, but also within the apoptotic cells themselves, 
suggesting a cell-autonomous component of motility. During the first 2 days of 
development, engulfment is rare, and most apoptotic cells lyse at the brain 
periphery. By 3 days postfertilization, most cell corpses are rapidly engulfed 
by macrophages. This engulfment requires the guanine nucleotide exchange factor 
elmo1. In elmo1-deficient macrophages, engulfment is rare and may occur through 
macropinocytosis rather than directed engulfment. These findings suggest that 
clearance of apoptotic cells in living vertebrates is accomplished by the 
combined actions of apoptotic cell migration and elmo1-dependent macrophage 
engulfment.