Figure 2.

Non-apoptotic role of caspases in NGF-dependent axon degeneration. Axon degeneration and pruning can be studied using a Campenot chamber ((a) top view and (b) side view). The chamber separates the soma (magenta) and neurite (green) chambers so that cells can be manipulated to either globally or locally deprive neurons of growth factor (NGF). Global withdrawal that results in neuron death (c) does not require Caspase-6, which is important for (d) local NGF withdrawal-induced axonal pruning. The role of IAP-binding motif proteins (IBPs), Bax, XIAP and Caspases-9, -3 and -6 have all been shown to regulate local NGF-induced axonal pruning. The activation of the pro-caspase 9 without Apaf1 and the mechanism of caspase-6 activation require further investigation. Current unknowns are represented by the question marks. DR, death receptor 6; p75, p75 neurotrophin receptor; IBP, IAP-binding proteins; Casp-9, caspase-9; Casp-3, caspase-3; Apaf-1, apoptotic protease-activating factor 1; XIAP, inhibitor of apoptosis 1 on X; Bax, BCL2-associated X; Bcl2, B-cell lymphoma 2 protein