Although infection by a virus, say, can trigger an untimely demise, individual cells also often self-destruct for a wide range of reasons, such as to prevent the spread of cancer. Described as apoptosis or programmed cell death (PCD), it’s been known about for some time but details about how this process works have remained elusive.
Importantly, PCD doesn’t just result in a suddenly exploding cell; rather, the destruction of its various components happens in a wave, cascading across the tiny structure. It's not been clear, though, what process drives this to occur.
Now, writing in Science, a pair of researchers from Stanford University have managed to observe what has been referred to as the “speed of death”, the rate at which a cell shuffles off its mortal coil. Turns out that this is around 0.03 millimeters (0.0012 inches) per minute. This doesn’t sound like much, but it's fairly rapid when you’re an egg cell no larger than 1.2 millimeters (0.047 inches) across.
The study explains that cells commence the onset of death using a technique not too different from the one that they use in life. Instead of using somewhat ponderous chemical diffusion for long-distance communication, they sometimes use “waves” of chemical activity: a conga line of chemical instructions that are relatively rapid. As it happens, the speed of death indicates that apoptosis uses chemical waves, rather than the slower diffusion method, which settles a long-standing debate.
It took some tricky engineering to find this out, though. First, the team chose to use an easy-to-see African clawed frog (Xenopus laevis) egg. Extracting the cytoplasm – everything within the cell but the nucleus – they then triggered cell death.
Now, cell death can be initiated by a substantial release of proteins, say from damaged mitochondria. This can initiate the mobilization of other proteins, that essentially dive bomb other mitochondria, which sets off a self-reinforcing feedback loop.
Even in large cells, this isn’t easy to observe, so the team put an otherwise intact cytoplasm sample, whose proteins had been dyed green, into a compartment with another that had already been through PCD, and whose proteins were tinged with a red hue. This tricked the former into engaging in PCD itself, and the team watched as the green was swamped by a red tidal wave – and thus, obtained the aforementioned death velocity.
It’s difficult not to be fascinated by death, the final curtain call awaiting every living thing. Such studies, whether focused on something larger like the brain, or smaller like individual cells, are really all about life, though.
By grasping how things perish, we better understand how to prevent them from doing so in the first place. If they're hostile cells, of course, we could always harness this knowledge to annihilate them.
[H/T: Science News]