[
Nature,
1996]
During the development of many, if not all, complex organisms, specific cells are marked out for elimination in a process known as programmed cell death, or apoptosis, a form of cell suicide. For example, during the development of the hermaphrodite nematode worm Caenorhabditis elegans, 131 of the 1,090 cells produced are genetically destined to die. Drosophila embryos without the necessary genes to execute this death programme do not survive. In vertebrates, failure to delete malformed or potentially autoreactive immune cells during development can eventually lead to autoimmunity or leukaemia. So too much or too little cell death threatens the whole organism.