Mutations in key components of apoptotic pathways are lethal. As a safeguard against disease, every cell in our bodies expresses the components of the apoptotic pathways and is ready for rapid self destruction. In fact, it has recently become clear that cells must receive the proper set of signals to prevent apoptosis or they will self destruct. The central machinery of apoptosis consists of a cascade of cysteine proteases called caspases . There are 2 major types of caspases, initiator caspases and effector caspases.
Effector caspases are the enzymes responsible for disassembling the cells.
The 2 most important initiator caspases are caspase8 and caspase9. These are associated with the 2 major pathways for initiating apoptosis. Caspase 8 is involved in receptor mediated apoptosis while caspase 9 is involved with the mitocondrial pathway. Mice deficient for either of these caspases usually die before birth and always within 3 days of birth. The mice show distinct defects for each caspase, some of which include brain deformities, heart malformations and blood overproduction.