More on Cellular Rejuvenation
Extension and the Reversal of
Today, I saw a bit farther into the challenge of the fountain of youth.
Background: Why Are Babies Born
Have you ever wondered why babies... and seeds and bacteria...are born young? Their parents have varying ages, and the germ cells they contribute to produce offspring are somewhat aged and somewhat damaged. We don't know any way to repair these ravages of aging. And yet, new organisms are born brand, spanking new! How does that happen?
It's clear that it does happen, and that the restoration is as complete and as accurate as only digital copying can make it. If it didn't happen, life could never have survived beyond three or four generations. (After three or four generations, offspring would be born so old that they would die of old age before birth.) And it must be accurate or species couldn't survive over millions of generations. (I realize that mutations occur, but the original species, such as cockroaches, can coexist unchanged (along with viable mutated species) for enormous numbers of generations.) How this "clean-up" and total restoration occurs I don't know, but it has to happen.
Although I had pondered this question for some few years, it struck home in April, 2000, when Advanced Cell Technology announced that they had cloned six calves from a somatic cell from a very old cow. The calves were born brand new, as is the time-honored way with baby calves. A critical fact about the cloned calves is that the nucleus of the ancient cow was implanted in an enucleated ovum. Whatever rejuvenated the fertilized ovum was either located in the nucleus of the old cow's cell or in the cellular body of the ovum.
So however Nature accomplishes it, she has a technique for completely restoring organisms to the blush of youth whenever they reproduce.
Just Because Reproducing Germ Cells Undergo Total Rejuvenation, Why Should We Think That Multicellular Organisms Can Be Rejuvenated in the Same Way?
Although complete restoration of undifferentiated cells takes place during cell division, it doesn't occur when differentiated cells divided. If it did, we wouldn't age.
A key question is whether what happens in germ cells when they reproduce can be made to happen in somatic cells that are already differentiated. I certainly don't know the answer to this question. My hope is that when total cellular restoration takes place, it comes about because a cascade of repair enzymes and proteins flood zygotes when they are fertilized (or unicellular organisms before(?) they fission). Hopefully, this cocktail of regenerative agents will work as well in differentiated cells as it does in undifferentiated cells.
What I Realized Today
Today, I realized that this rejuvenation must take place for protozoa which reproduce by fission as well as other unicellular organisms. If an amoeba fissures into two amoebae, both must be restored to a pristine state or the species would die out after a few generations.
Rejuvenation Must Always Have Been There
That means that this rejuvenation during reproduction extends across all species. It is essential to the existence of life, and it has been conserved throughout the entirety of the evolution of life on Earth. It's been there from the beginning. The first living organism on Earth must have had to ability to restore its offspring to a pristine state. And this means that it's found in every cellular organism.
It seems probable to me that this cellular refurbishment may be initiated by the action of a single gene common to all life on Earth. If so, that should make its identification easier. Some organisms have only a few chromosomes, and should make it easier to identify a common "trigger" gene.
If it isn't housed in nuclei, then it has to be somewhere in the extra-nuclear cell.
No One Fails to Age... Do They?
One interesting fact about aging is that we don't see anyone "falling through" and remaining ageless, or backing up their ages*. Whatever mediates aging operates infallibly. If there's a single gene that can turn on and reverse aging, it never happens. Or does it? If it happens in individual cells, they might revert to an early state, but all the others would age normally. How could we tell?
* - Poul Anderson has written stories about rare people who never age, and who learn to keep a low profile, moving from place to place as necessary to avoid detection, and to survive troubled times.