‘Hedgehog’ comets can be produced by treating cells with 0.1 M H2O2 for 5 min on ice (no chance for induction of apoptotic processes) and immediately processing for the comet assay. If the treated cells are incubated for half an hour, ‘hedgehog’ comets are no longer seen – the DNA damage has been repaired by the cell. Therefore hedgehog comets do not necessarily indicate apoptosis. In fully developed apoptosis, fragmented DNA is so small (down to nucleosome-sized pieces) that it would disappear completely by diffusion. But hedgehogs might be a sign of apoptosis in certain cases, indicating limited fragmentation (i.e. the earliest stages of apoptosis).

[Comet ‘ghosts’ – faint images with just a small percentage of normal DNA stain – are sometimes seen. Perhaps these are apoptotic cells?]

In summary, hedgehogs may be a good indicator of apoptosis if you already are sure that apoptosis is in progress – but in that case you won’t need hedgehogs to tell you.

"FAQ by Andrew Collins, Gunnar Brunborg and Jonas Nygren, 2006, NewGeneris FP7-project"