19 July 2018 – Many free-living flatworms have a superpower – the ability to regenerate. Due to large numbers of pluripotent adult stem cells, flatworms continuously rebuild themselves in a food-supply dependent manner, and amazingly, they can regenerate in their entirety even after having been chopped into small pieces. This makes them an ideal model to study not only the mechanisms of regeneration, but also stem cell biology, ageing, and how body size, shape and proportions are laid down and maintained.
Flatworm aficionados Eugene Berezikov and Jochen Rink first bonded over drinks at a conference in 2012, when they discovered a mutual fascination with the idea that besides the small number of haphazardously chosen model species currently in use, there were likely to be many more interesting flatworm species waiting to be found. Since then, wild worm hunting has taken the two researchers to exotic locations all over the world.
Berezikov and Rink had different reasons for their wish to find new worms. Berezikov studies macrostomids, and was unhappy with the current lab species, Macrostomum lignano, whose genome is too complex for straightforward genetic manipulation. Rink studies planarians, which come with a spectrum of regenerative abilities – some species, including the lab model Schmidtea mediterranea, regenerate very efficiently, but others have little or no ability to do so. Comparing the different species might be the key to unlocking the puzzle of why regenerative abilities vary so much among animals.
Their first field trip together, to the Caribbean island of Curaçao in 2015, was driven solely by logic insists Berezikov: “The impetus was that the water temperature is much higher there, and therefore worms are likely to develop faster, which is a very desirable trait in a potential model species”. The two researchers poked around on the seashore for macrostomids with great success, but their search for planarians was more of a challenge. “I had to climb down a well to find them,” says Rink. “It’s basically a desert island and looking for freshwater planarians was not exactly straightforward.”
Since then, the two have refined their search criteria. “We’ve learned over the years that macrostomids like protected beaches on little river estuaries,” Rink says. “Google Earth is now a very important tool for us.” They have since been to India, Japan and Siberia, are keen to sample the East African lakes, and will shortly be returning to Curaçao and Aruba.
Siberia offered a particularly adventurous trip. “We wanted to find a species that could survive freezing,” says Berezikov, “so Siberia seemed to be a good place to look.” Rink relished the chance to visit Berezikov’s homeland: “We spent about a week driving through Northern Siberia together and camping out by the streams,” he says. “We were sampling planarians in abandoned sites from the Soviet era in the middle of nowhere – there were still buildings but everything was overgrown. There was a real ‘Mad Max’ feeling to it!”
The expeditions are also paying off in terms of scientific benefit. Berezikov has achieved his aim of finding a far better lab model, which he has already sequenced in collaboration with Rink, and with over 70 planaria species in the bag, Rink’s lab has begun to unravel the mechanism behind the differences in regeneration ability: it hangs on the balance between sexual and asexual reproduction, and there are strong hints as to the signalling pathways involved.
Both researchers emphasise that being EMBO Young Investigators has enhanced their collaboration. Subsidised access to the genomics facilities at the European Molecular Biology Laboratory in Heidelberg has been invaluable, but the intellectual stimulus of the Young Investigator meetings also stands out: “The annual meetings are my out-of-the-box-thinking week,” says Rink. Berezikov agrees: “you go there to meet great colleagues and hear great science from all the different fields of biology – I really cherish it,” he says.
Will the expeditions continue? Definitely, says Rink. “We’ve only really run into one big problem – Eugene snores! But I now have a good pair of earplugs, so we should be fine.”