An immortal worm isn't exactly what comes to mind when researching how to live forever, but this inconspicuous creature could hold some very valuable clues on eternal youth.
Biologists from University of Nottingham spurred this big debate in 2008 when they claimed their object of study, the planaria or "flatworm" might actually be immortal. Essentially, this worm possesses an indefinite ability to regenerate its cells and thus practically never grow old. In fact, not only does the worm stay immortal -- but it stays forever young.
This claim couldn't go unnoticed and it wasn't long before other scientists took note of this. That's when the essential question was put: how do you really know that they're immortal?
It's a simple question, with an extremely complicated answer. To answer this question, you must first define what makes an animal immortal in the first place. Simply standing by an allegedly immortal animal waiting for it to die is far from being practical at all, in scientific terms.
So instead, scientists have identified a number of genetic criteria which need to be filled in order for an animal to be considered immortal. That's when things got really interesting.
Table of contents
A common worm with uncommon abilities
Planarian worms are relatively common. They're spread across several continents and can live in both in various environments. Some species inhabit aquatic and saltwater and freshwater ponds and rivers. Others are terrestrial and live under logs, in or on the soil, and on plants in humid areas.
Biologists use planarian worms a lot in research. Ironically, they do this because the worms the ability to regenerate parts of their bodies when needed.
Take a worm and cut out a body part -- it will grow a new one. Cut it lengthwise or crosswise, it will regenerate into two separate individuals. This mind-blowing ability is empowered by pluripotent stem cells that have the ability to create all the various cell types that these worms need to regenerate.
But scientists still need more to definitely say that a creature is immortal.
What makes an immortal worm
First of all, it needs to retain the ability of replacing old cells with new cells indefinitely, and this is what stem cells are for.
Most animal in the world gradually tend to lose this ability as they age. This causes them to get older and function improperly. The flatworm not only is able to regenerate its old, dead cells, but it can literary grow a new brain, gut or tail when severed in two.
Over the course of their several year long research, Notthingham University scientists have cloned a few thousand individuals from one single flatworm that they cut in two. They then cut the resulting two individuals in two and so on so forth. Biologist Dr. Aziz Aboobaker, who heads the project explains:
“We’ve been studying two types of planarian worms; those that reproduce sexually, like us, and those that reproduce asexually, simply dividing in two,” said Dr. Aziz Aboobaker from the University’s School of Biology. “Both appear to regenerate indefinitely by growing new muscles, skin, guts and even entire brains over and over again.
This was very unexpected.
“Usually when stem cells divide — to heal wounds, or during reproduction or for growth — they start to show signs of aging. This means that the stem cells are no longer able to divide and so become less able to replace exhausted specialized cells in the tissues of our bodies.
“Our aging skin is perhaps the most visible example of this effect. Planarian worms and their stem cells are somehow able to avoid the aging process and to keep their cells dividing.”
The key lies in DNA
When a cell normally divides, the tip of its DNA, called the telomere, gets shorter. An enzyme called telomerase regenerates the telomores.
However in most sexually reproductive organisms it is only active during the organism's development. Once it reaches maturity, the enzyme stops functioning, and the telomeres become shorter and shorter until cell replication is made impossible, otherwise the DNA would become too severely damaged.
But our immortal worm is able to maintain telomere length indefinitely so that they can continue to replicate. This is a 'gold' standard in establishing whether an animal is immortal. Dr. Aboobaker and colleagues were able to demonstrate that the flatworms actively maintain the ends of their chromosomes in adult stem cells, leading to theoretical immortality.
Doctoral student Thomas Tan performed a series of crucial experiments, as part of the project, in order to scientifically explain the worm's fascinating, yet theoretical, immortality. A possible planarian version of the gene coding for the telomerase enzyme was identified, and had its activity turned off. Since the telomere shrank in size, it was thus confirmed to be the right gene.
With this new found knowledge, the scientists monitored and measured the gene and observed that asexual worms dramatically increase the activity of this gene when they regenerate, allowing stem cells to maintain their telomeres as they divide to replace missing tissues.
"It was serendipitous to be sandwiched between Professor Edward Louis's yeast genetics lab and the Children's Brain Tumour Research Centre, both University of Nottingham research centres with expertise in telomere biology. Aziz and Ed kept demanding clearer proof and I feel we have been able to give a very satisfying answer," Dr. Tan stated.
There are both sexual and asexual planaria. Sexual planaria are hermaphrodites, possessing both testicles and ovaries. But it's the asexual ones that exhibit the striking regenerative abilities.
“Asexual planarian worms demonstrate the potential to maintain telomere length during regeneration. Our data satisfy one of the predictions about what it would take for an animal to be potentially immortal and that it is possible for this scenario to evolve. The next goals for us are to understand the mechanisms in more detail and to understand more about how you evolve an immortal animal.”
The same didn't apply to sexual flatworms, though, which still, however, display the same apparently indefinite ability to regenerate. The researchers explain that either these flatworms will eventually shorten their telomeres, albeit very gradually, or they found a different way to maintain indefinite cell replication that doesn't involve the telomerase enzyme.
This suggests that there could be some extra difficulties when translating these abilities from worms to other creatures. But it doesn't necessarily make it impossible.
From immortal worms to immortal humans
The researchers claim that the next natural step is to study how this might apply to more complex organisms, like humans.
“The next goals for us are to understand the mechanisms in more detail and to understand more about how you evolve an immortal animal,” said Aboobaker.
“The worms are a model system in which we can ask questions, like is it possible for a multicellular animals to be immortal and avoid the effects of aging?"
“If so, how does this animal do this in comparison to animals that don’t? Of course we hope that this impacts humans, that’s why we do it. But we aren’t planning on making any drugs or medicines… other people are, I’m sure.”
The quest to uncover the mysteries of the this immortal worm and its mind-boggling regenerative powers is underway, and it promises to be a fascinating voyage of discovery. Unraveling the secrets held within its tiny form may help science grapple with some of the most fundamental questions about life, aging, and perhaps even immortality.
The findings were published in the journal PNAS. University of Nottingham PR.