Three years ago, a two-headed worm returned from the International Space Station (ISS), and in the summer of 2017, the worm achieved internet and popular media fame when researchers from Tufts University published a paper describing the worm and other results from their ISS U.S. National Laboratory experiment.
The story behind this mutant worm, however, is even more rich than its delightfully deformed morphology. The payload that carried the famous worm and 77 of its relatives to the ISS and back inspired researchers, payload specialists, and even FedEx to take the first steps toward new scientific discoveries and processes that now have their own successes to share, all of which was pioneered by these first worms—planarian flatworms, that is—in space.
THE WONDER OF WORMS
Planarian flatworms have been studied since the 1800s as a model for genetics, body patterning, and neuroscience. The flatworms have a “true brain,” unlike earthworms and other species in which the nervous system is more spread out and less well-developed.
Because of their brain’s bilateral symmetry, their genomes, and other factors, planarian flatworms are more similar to our human ancestors than some of the more derived model systems such as flies or Caenorhabditis elegans (nematodes), said Michael Levin, director of the Allen Discovery Center at Tufts. This model system is being used to understand regeneration, stem cell regulation, and behavior. The worms are also popular for drug addiction research because they have most of the same neurotransmitters as humans, so they exhibit symptoms of withdrawal and addiction to the same drugs.
Levin’s lab, however, uses the worms to study how physical forces influence body patterning, the process through which an organism ensures that cell types and body structures are properly shaped and placed during development. Planarian flatworms are a unique model for such studies because they are incredibly robust regenerators and yet they are mixaploid—their cells accumulate a plethora of mutations from constant regeneration and non-sexual reproduction.
“There’s not even the same number of chromosomes in every cell of a single worm,” said Levin. “How can your genome be such a mess and yet you retain this beautiful ability to create a perfect, correctly shaped planarian every time? Through our work over the last 15 years, the worms are telling us that patterning is controlled by very interesting biophysical dynamics.”
In other words, because the DNA of planarian flatworms can diverge widely and yet their anatomy remains intact, their cellular decisionmaking is revealing novel aspects of how genetics and physics cooperate to control dynamic anatomy. Levin and his team studies the role of bioelectric signals—electrical communication between individual cells—in determining anatomy. They created the first-ever line of stable patterning mutants in planarians by editing their natural electrical signals, said Levin. In doing so, the team showed that it is possible to re-write electrical pattern memories to control anatomy.
Over the long term, understanding these processes may shed light on how biophysical dynamics are involved in the development, aging, and modification of body plans in higher organisms—and how we might use bioelectric and other signals to control cell behavior. Beyond myriad benefits in discovery science, the power to control cell fate with bioelectric signals could ultimately allow manipulation of regenerative or developmental processes involved in human health. For example, perhaps doctors could use this knowledge to accelerate wound healing, grow organs outside of the body for use in transplants, slow negative effects of aging, prevent certain birth defects, or improve treatments for neurodegenerative diseases.
A notable player in biophysical dynamics is the geomagnetic field, or GMF. This natural characteristic of the Earth imposes a magnetic field of approximately 0.5 Gauss onto all living organisms. The GMF changes very large areas, so it may seem unintuitive that organisms sense and use it in their daily behaviors. However, experiments on plants, animals, and cells in culture show that they do sense and respond to changing magnetic fields, and some classic examples (such as migrating fish and birds) demonstrate ways in which organisms perceive and use Earth’s magnetic field lines. Despite these data, it is unknown how and why embryonic cells (like the stem cells of a regenerating planarian) sense the GMF.
In laboratory model organisms that are shielded from the GMF by metals and other techniques, “all kinds of things go wrong,” Levin said. “Cells are counting on this field for something, and we have no idea what.” The unique GMF conditions onboard the ISS are what prompted Levin to seriously consider an unexpected opportunity to send worms to space.
The opportunity was borne of a search for innovation. The nonprofit Kentucky Space, LLC was seeking white papers from new-to-space investigators interested in using microgravity to tackle big research questions—to spark their imagination in the early stages of the nonprofit learning how to enable research onboard the ISS.
“We heard there was this group from Kentucky that was doing some space stuff, and they were interested in sending worms to space,” said Junji Morokuma, who joined the Levin lab in late 2004 and subsequently worked on the space worms project. “I thought ‘oh wow,’ but we weren’t sure what to do or what we would find.” There was some research on worms in simulated microgravity that had shown a strong increase in regenerative capacity, he said, but there had been no planarian flatworms in space to shed light on what the team should expect.
So the team kept it simple, said Levin, and set out to determine how the combined components of space travel might affect regeneration in the worms. These components included takeoff, acceleration, splashdown, vibration, microgravity, and, of course, the altered geomagnetic field. These physical forces perturb how the cells talk to each other and thus can influence the pattern formation within cells of a regenerating worm. “It’s not zero GMF,” Levin said, as it is in ground-based shielding experiments, “but it’s different, and we didn’t have any clue what we might find.”
BREAKING NEW GROUND
As the first-ever space-faring planarian flatworms unknowingly prepared for their launch onboard commercial resupply services (CRS) vehicle SpaceX CRS-5, Kentucky Space and the Levin lab tackled a variety of their own firsts.
“Space business and research is exciting, but there’s lots of money, paperwork, delays, and ‘oops’ involved,” said Morokuma. “I’ve heard to launch a rocket, you need paperwork taller than the rocket,” he laughed, “but luckily Kentucky Space handled all of that.”
Kris Kimel, founder of Kentucky Space and co-founder of its for-profit spinoff Space Tango, acknowledged that early experiments like the space worms, while simple in design, played a critical role in allowing his team to “learn the ropes” with respect to payload integrations, interfacing with NASA, and dealing with customers.
“This experiment was a really important one for us,” said Kimel. “We learned a lot technically from the payload as well as how to protect the end user from some challenging processes. This experience laid the philosophical bed for what became TangoLab and our successful business ventures as Space Tango.”
Supported by CASIS sponsorship, the worms launched on January 10, 2015, spent several weeks onboard the ISS National Lab, and returned exactly one month later.
Prior to return, Kentucky Space also worked with Levin and new partner FedEx Space Solutions to arrange delivery services for the worms back to the lab following splashdown. “The logistics were really interesting,” said Levin. “I’ve never weighed a flatworm. I understand why they needed that data, but it was kind of wild.”
David Drees, who managed the flatworm delivery process for FedEx, said his primary concern was returning the worms as rapidly as possible after splashdown so the team could analyze the worms before they readjusted too much to Earth’s conditions. Some of this depended on temperature. “We needed to keep them not warm enough for cell division but not cold enough to kill them,” said Drees.
The rest was timing. “We have a great infrastructure at FedEx, but we run on schedules,” said Drees. “The capsule coming down from the ISS is not on a schedule we can predict months in advance. It could come down any time of day or night, and we’ll get maybe three hours’ notice.” To adjust to this uncertainty, resources from several FedEx operating companies were activated, and a FedEx Express courier was on standby.
Adding to the lists of firsts on the space worms’ resume, this was the first payload that FedEx executed as a “rapid return,” in which they intercept returning experiments during the handoff from launch provider to NASA, in this case at an airport on the California coast.
“It was a new thing, so I actually went out there and personally worked with Kentucky Space as they took possession of the box with the worms from the NASA plane,” said Drees. “I was a space geek growing up, so it was a really cool thing to be a part of.” From there, the box was fitted with a “SenseAware” device that sends information on location, pressure, light, moisture, and temperature to a customer web portal—and then, since it was 11 p.m., it went to a FedEx station for the night.
“Our operations folks really stepped up to handle a nontraditional shipping situation,” said Drees. “Everyone was really proud to play a small part in the experiment.” The worms’ proof-of-concept “rapid return” helped FedEx develop this service as a new product offering to its customers, with an entire system now developed for this purpose. “Space worms was the prototype!” said Drees.
A DARK AND MURKY JOURNEY
Meanwhile, back in Boston, there was a blizzard as the Tufts team waited for the new FedEx delivery process to return their box of worms from the ISS (via Long Beach, California).
Normally, the worms would routinely receive fresh water and be exposed to light when they were fed and cleaned twice a week. But to keep the initial experiment as elegant and simple as possible, none of these elements were preserved in the spaceflight experiment or ground controls. Because the goal was to evaluate regeneration, the worms were merely cut into thirds, placed into the approved container and space-certified hardware, and loaded onto the SpaceX rocket.
For the weeks they were in space, we’d had no way of monitoring them,
so we didn’t have any clue what we would find,” said Levin. “I mean, they were up there without any supervision. Our biggest concern was that when they got back they’d all be dead.”
“We basically shoved a lot of worms into a test tube, which went into a sealed coffee-can-sized container,” said Morokuma. “Temperature was controlled to some degree, but that was it.” As promised, the postflight box arrived, and the team gathered to see whether their planaria pioneers had successfully re-grown and survived—and what stories they had to tell. “We got this box that came from space, and we were all very excited to open this box,” said Levin, “and sure enough, they were alive!”
Immediately, the team witnessed the first interesting behavior of the space worms. When they took the worms out of the dark, stagnant water from their long journey and placed them in normal water, the worms’ bodies curled. Normally, this type of curling response indicates that worms are unhappy with their environment, said Levin. “It was amazing. We put them into this beautiful, fresh Poland Springs water they normally love, they all curled up like they didn’t like it,” he said, “like they had gotten used to the stinky water—which is really strange.”
Then of course, as the team examined the individual worms more closely, they noticed the now-famous two-headed worm—which later garnered acclaim in mainstream media outlets including Gizmodo, CNET, CBS News, Fox News, Engadget, Yahoo, and Smithsonian Magazine.
Beyond being visually captivating to the public, this phenotype is statistically significant. “Planaria are robust, stable regenerators,” said Levin. “You’d have to cut thousands of these kinds of worms on the ground to see two heads.” This was the first indicator that something indeed was unique about the regenerative environment onboard the ISS.
Yet as unexpected and interesting as these early findings were, the most astounding results from the space worms study would not be seen for more than a year, when the team examined the worms’ behavior 18 months after readjusting to normal Earth conditions.
MORE THAN JUST A BOX OF WORMS
At first look after 18 months of reacclimation, the worms remarkably had a different complement of bacteria than their relatives who had remained on Earth. As with the human microbiome, the population of microorganisms in a worm’s gut, on its surface, and in its surroundings intimately influence bodily functions and behaviors.
According to Levin, until this point, no one had really studied planarian flatworm microbiomes—though some studies on their immune systems and response to infection may yield insights into the role of the microbiome. Inspired by the space worm results, however, Levin and collaborators are currently finalizing the first study of the native planarian microbiome, in terms of what the complement of bacteria typically looks like in standard populations and why it matters.
The second curious and remarkable behavior of the retired space worms suggested an atypical fear of the dark. “Normally, worms dislike the light,” said Levin. “They’re sort of photophobic and try to get into as dark a corner as they can.” After 1.5 years of experiencing normal lab conditions on Earth, however, the space worms showed a notable and unusual preference for light.
“Planarian flatworms are amazing in that they are, in effect, immortal—they don’t age,” said Levin. “They have stem cells that continuously repopulate the animal as somatic cells age and die off.” Within approximately one month, most of a worm’s cells have to be renewed. Yet 1.5 years after spaceflight, after 18 such turnovers, the space worms still showed an imprint of their unique experience, moving toward and sitting in the light far more frequently than control worms.
“This is of course conjecture at this stage, but one possibility is that they remember that long,” said Levin. “Another possibility is that it’s related to the microbiome change.” Evidence of the microbiome changing organism behavior and acting as a cognitive modulator has been seen in other animals and even humans, according to Levin.
However, more studies are needed to answer these and other questions about the influence of the ISS environment on planarians.
“The worms are telling us that the experience of going to space profoundly alters the mechanisms within the regenerative process—patterning, differentiation, and cell migration,” said Levin. “But we need to understand how these effects are exerted if we are to work toward modulating regeneration for useful purposes on Earth.”