Apaf-1 is acetylated and open in young neurons (P5) but methylated and silent in mature neurons (P28). Its derepression allows older neurons to apoptose (bottom, left to right) upon release of cyt c (white).
Neurons die off by the handful during development, when their proliferating brethren can easily replace them. But once neurons mature, they shut off proliferation pathways, and survival becomes precious. One way older neurons become less sensitive to apoptosis is by preventing a protein called Bax from reaching mitochondria, where it pokes holes that let out cytochrome c (cyt c). The new findings identify an additional protective step downstream of cyt c release.
Older sympathetic neurons survived injections of cyt c because they had less Apaf-1, a protein that recruits cyt c to the...
