This odd word designates the process by which cells can die without causing harm to the adjacent tissues. That’s why it’s a complicated and regulated physiological mechanism. Indeed, it’s tough to tell how many cells our bodies produce each day, but one thing is sure : it’s a big number. So cells do have to die in order to regenerate tissues.
Apoptosis will involve a cascade of protein activations which implies the cleavage of these proteins. Cleaved proteins can be tagged and observed using a fluorescence microscope. Above, cells on the left are left untreated, cells on the right were treated with Staurosporine. With green and red dyes we can see proteins, alpha-tubulin and phospho-H3 histone, involved in proliferating cells. On the right, the blue dye shows cleaved PARP, a major marker of apoptosis. In short, these cells are dying.