Tag Archives: flatworm

Scientists play with a flatworm and grow another species’ head instead

Tufts biologists induced one species of flatworm -- G. dorotocephala, top left -- to grow heads and brains characteristic of other species of flatworm, top row, without altering genomic sequence. Examples of the outcomes can be seen in the bottom row of the image.

Tufts biologists induced one species of flatworm — G. dorotocephala, top left — to grow heads and brains characteristic of other species of flatworm, top row, without altering genomic sequence. Examples of the outcomes can be seen in the bottom row of the image.

It sounds like a plot from Frankenstein, but apparently there’s no limit to how versatile flatworms can be. Previously, researchers at Tufts University  determined that the small, yellow worm can retain its memories after it head was severed. As a reminder, flatworms can regrew new heads following decapitation. Now, the same team yet again guillotined some flatworms and interrupted gap junctions, which are protein channels that enable cells to communicate with each other by passing electrical signals back and forth – just to see what would happen. Yes, the flatworm grew a new head, but it was that of another flatworm species. They eventually induced the same flatworm species to grow the heads and brains of multiple other, closely related species. There’s a lot of biology and behaviour encoded in genes, but these findings show that tweaking physiological mechanisms in a live body can actually cause new anatomical developments. We might have uncovered a new form of epigenetics.

“It is commonly thought that the sequence and structure of chromatin – material that makes up chromosomes – determine the shape of an organism, but these results show that the function of physiological networks can override the species-specific default anatomy,” says the paper’s senior and corresponding author Michael Levin, Ph.D., who holds the Vannevar Bush Chair in biology and directs the Center for Regenerative and Developmental Biology in the School of Arts and Sciences at Tufts. “By modulating the connectivity of cells via electrical synapses, we were able to derive head morphology and brain patterning belonging to a completely different species from an animal with a normal genome.”

The researchers at Tufts worked with  Girardia dorotocephala – a flatworm species known for its extraordinary regenerative capability. After severing the head, the researchers introduced a transient perturbation of physiological connectivity among cells. Despite the worm had the same genome, once it started to regenerate a new head its morphology, and consequently that of the brain, was altered. By varying this disturbance the researchers grew heads that resemble those of flatworm cousins. The closer the two species were related, the easier it was to effect the change, suggesting there’s an evolutionary connection that allowed these worms to morph their body parts. You can see from the picture posted above just how insanely close the worms grew their heads similar to other species.

Oddly enough, this change is temporary. Weeks after the planaria completed regeneration to the other species’ head shapes, the worms once again began remodeling and re-acquired their original head morphology.

The flatworm is really an inexhaustible well of wisdom. For instance, they’re the primary object of study for researchers working the field of longevity. Some claim that flatworms are immortal. 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. Both cut ends grow into a new individual. Over the course of their several year long research, Notthingham University scientists have cloned a few thousand individuals starting from one single flatworm that was cut in two, which were also at their own term cut in two, and so on so forth. What can we learn from the flatworm’s latest trick? Well, doctors might find a way to fix birth defects or cause new biological structures to grow after an injury, according to Levin. “These findings raise significant questions about how genes and bioelectric networks interact to build complex body structures,” he says.

 

planaria

After being decapitated, flatworms not only grow back their head but also regain memories

Research on nematodes have always been convenient for scientists. For one, they grow and breed really fast, making them ideal for work pertaining to genetics. Some of them have amazing properties, like  the planaria or “flatworm”, which some scientists believe it possesses the indefinite ability to regenerate its cells and thus practically never grow old. It soon became the object of intense research as scientists are trying to unravel the key to its longevity and whether or not it could be possible to transfer it to humans.

The planaria’s startling regenerative abilities don’t end here apparently. Researchers at Tufts University have determined that the small, yellow worm is able to grow back a lot more than just its lost body parts: it can regain its memories too!

The idea was first suggested sometimes in the 1960s, however it was extremely cumbersome for scientists to prove at the time. Now, Tal Shomrat and Michael Levin at Tufts University built a computerized apparatus for training planarians that allowed them to to study planarian memory with less error and greater numbers of worms.

planaria

These small worms detest open spaces and bright lights, however some of them were trained by the researchers to ignore these stimuli and make their way through them to reach food. After decapitating specimens and after the worms grew back their heads, they were inserted back in the experimental set-up. Even after decapitation, worms that had gone through training were able to overcome their fears and start eating much faster than worms that hadn’t been trained. The scientists made certain that no bit of brain survived during the decapitation process.

It’s worth nothing, however, that the memories didn’t come back immediately. The researchers still had to teach them to ignore the bothersome stimuli, but only once, like a sort of reminder if you will. How is such a thing possible though? It’s still unclear how, but the scientists suggest the planaria might store their memories in various parts of their bodies, not just in the head. Alternatively, they suggest that the worms’ original brain may have modified their nervous systems, and their nervous systems may have then altered how the new brains formed during regrowth.

Levin says epigenetics may play a role—modifications to an organism’s DNA that dial certain genes up or down—”but this alone doesn’t begin to explain it.”

“We don’t have an answer to this,” he says. “What we do show evidence of is the remarkable fact that memory seems to be stored outside the brain.”

The study was reported in The Journal of Experimental Biology

flatworm

Scientists prove ‘immortal worms’ can regenerate indefinitely and stay forever young

flatworm

University of Nottingham scientists spurred a slew of debate in 2008 when they claimed their object of study, the planaria or “flatworm”, might actually be immortal, possessing an indefinite ability to regenerate its cells and thus practically never grow old. In fact, an important distinction must be made, it’s not that the flatworm never grows old that’s interesting, it’s the fact that it stays forever young!

As you can imagine a discovery of such interest didn’t go unnoticed, and it wasn’t long before the essential question was put – how do you really know that they’re immortal? 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. The researchers identified a number of genetic criteria which need to be filled in order for an animal to be considered immortal. 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, thus causing them to get older, function improperly and eventually die. 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. Both cut ends grow into a new individual. Over the course of their several year long research, Notthingham University scientists have cloned a few thousand individuals starting from one single flatworm that was cut in two, which were also at their own term cut 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.

“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

Each time a cell 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. An immortal animal is able to maintain telomere length indefinitely so that they can continue to replicate, and 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. Armed 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.

From immortal worms to immortal humans

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.

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 findings were published in the journal PNAS. University of Nottingham PR