In what sounds like a plot line from a BioShock game, a team of biologists has coaxed an animal into growing a new head and brain resembling those of a different species. The bizarre accomplishment adds to a growing body of research highlighting the importance of non-DNA factors — collectively known as the 'epigenome' — in determining the most fundamental aspects of an organism's anatomy.
The animal in question is Girardia dorotocephala, better known as planaria. You might remember this little flatworm from any number of diabolical high school science experiments. Gifted with the ability to grow an entirely new body from a small fragment of itself, the planaria is something of a poster child for biological regeneration. As such, countless of the spade-headed worms have been minced to pieces in the name of teaching and learning.
But according to a new study led by Michael Levin of Tufts University and published today in the International Journal of Molecular Sciences, we haven't been giving this little worm enough credit. Planaria don't just do a bang-up job regenerating their own anatomy — they can be coaxed into expressing other forms. What's more, we don't have to mess with their DNA code at all to do so.
Biologists induced G. dorotocephala (top left) to grow heads and brains resembling other species (top). The results can be seen at the bottom. Image Credit: Tufts University
Instead, after decapitating their hapless test subjects, Levin and his colleagues tinkered with the worms' gap junctions — protein channels that cells use to communicate with each other. The result? "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," Levin said in a statement. In other words, holy gee, we turned this worm's head into another head.
Perturbing gap junctions not only influenced the overall shape of the planaria's head, but the shape of the brain and distribution of the worm's adult stem cells, as well. Perhaps unsurprisingly, it was easier to coax planaria into growing new heads resembling those of close genetic relatives than more distant cousins.
In another fascinating twist, the anatomical changes weren't permanent. Weeks after growing a new head, the head's features began reverting their natural morphology (and I can't stop picturing a lumpy-faced Harry Potter muttering curses as the effects of Polyjuice Potion wear off). More work is needed to figure out why, but the results so far highlight cell communication as a promising field of research for developmental biologists. Write the researchers:
While the genome is the source of all structural material in the organism, gap junctions provide unique conduits for using physiological and bioelectrical signals to link cells into information-processing networks, and are therefore ideal complements to genetically-encoded programs. We show that a relatively simple physiological perturbation can derive distinct species-specific morphologies from the same genome, highlighting an important layer of control between the genetics and the anatomy of an organism.
Who knows — perhaps these shapeshifting worms are the key to eventually figuring out how to reverse-engineer birth defects and unlock biological regeneration in more complex animals, even humans. It's a distant goal, and we may have to decapitate thousands more worms to get there, but that's science, baby.