Figure 2: Inducible Caspase 9 (iCP9), a modified version of the endogenous, pro-death Caspase 9, enables experimental control of the cell’s apoptotic program. (A) Activation of iCP9 is controlled in space and time by separate administration of a synthetic compound (termed ‘chemical inducer of dimerization’ or CID), which was designed to activate iCP9 and ultimately the apoptotic death cascade. CID is a small, hydrophobic FK506 analog that crosses cell membranes and binds to the FKBP domain (green) fused to the catalytic domain of Caspase 9 (red). (B) As with other genetic models, an oligodendrocyte-specific promoter such as myelin basic protein (pMBP) confers specificity of programmed cell death.