Developmental Biology Unit group leader studies 'immortal' flatworms to better understand the mechanisms that determine animal size.
Hanh Vu may not be the newest group leader at EMBL, but we’d be remiss not to introduce a researcher whose collection of flatworms seems to grow, well, as much as some of the flatworms themselves do. From many of the smallest to some of the biggest planarians, Vu aims to more clearly identify and understand genetic, metabolic, and environmental factors that govern the flatworms’ very diverse lengths. We caught up with Vu, who shared a bit more about these unusual flatworms that grow and grow while being fed, but shrink in size when their food source is taken away. Not only are planarians unusual, but they provide a unique opportunity to study the factors that govern an organism’s size.
Tell me about your group’s research.
Body size is one of the most characteristic features of animals, yet why some animals are small and others large remains an unanswered question. The primary goal of our group is to tackle this problem using planarian flatworms as model systems.
Why planarian flatworms? Why is it such a good model system?
Despite looking very simple, planarians actually have a very complex anatomy. They have complicated nervous systems, a gut system that spreads throughout the body, and an excretory system similar to human kidneys. Additionally, their bodies are full of pluripotent stem cells, which give planarians remarkable abilities – most famously, regenerative capabilities. Much like in the ‘Sorcerer’s Apprentice’, no matter how many pieces you cut a planarian into, each piece will regenerate into a new worm, just smaller. Interestingly, if you cut them into big pieces, you get bigger worms. Smaller pieces yield smaller worms. So, it makes for a good paradigm to study size-specification beyond what happens during embryonic development. Planarians also don’t have a fixed body size. So if you keep feeding a planarian, they keep growing bigger. If you stop feeding them, they don’t die, they just get smaller again. And this can happen indefinitely because planarian flatworms are, practically speaking, immortal.
What’s the size range of planarian?
The species most labs work with can be as short as 0.5 mm and as long as 25 mm, which corresponds to a 40-fold difference in body length or a 20,000-fold difference in body mass. Such a big difference in a single species is very interesting. And if you go out into the field, you can find hundreds of different species with a wide range of shapes and sizes living in marine, freshwater, and terrestrial habitats. For some reason, land planarians are largest and one species from Japan – Bipalium nobile – can even reach 1 m in length.
Why is EMBL the right place for this kind of research?
At EMBL, with its highly diverse research groups and world-class core facilities, I can take my science in exciting new directions that were not possible before. First, in close collaboration with the Dorrity group, Dyer group, and the Genomics Core Facility, we are trying to understand how body size is encoded in the planarian genome. Second, we are exploring the role of muscle mechanics in size control together with the Prevedel and Erzberger groups. On top of all this, EMBL’s new push toward studying life in context gives us a wonderful excuse to keep collecting more species from different environments around the globe, which of course infuses all of our projects with a comparative biology angle.
These planarian sound like something out of science fiction. Are you a fan of science fiction in general?
You’re absolutely right! It’s almost as if they are made up. And yes, I do like science fiction. I think the first science fiction movie I ever saw and enjoyed was probably Star Wars, but unfortunately no planarian there. More recently, I’ve really enjoyed the first seasons of Westworld.
When you aren’t busy tracking down, growing, and studying planarians, what do you do for fun?
To be honest, between starting my lab and chasing a two-year-old around, I don’t seem to have a lot of spare time these days! In the past, though, I really enjoyed making things from paper, like origami animals. My grandfather used to come and stay with us, making all kinds of animals. The one I make best is probably the crane.