Frog stem cell research changes what we know about how organisms are built

An image of what the research team is calling “synthetic living machines,” or “xenobots.” (Doug Blackiston/Tufts University)

What defines how an organism is built?

When biologists from Tufts University and the University of Vermont took stem cells out of the embryos of African clawed frogs and allowed them to develop independently, they revealed a new answer to that question.

Their paper, published in the journal Science Robotics, details the strange history of what the team is calling “synthetic living machines,” or “xenobots.”

The scientists targeted stem cells that had already differentiated into skin cells, then took them from their embryos. Outside of their original home, the cells first clustered into clumps, then organized themselves into different shapes than the ones their frog genome would normally call for.

In the context of an embryo, the stem cells would have grown cilia, tiny hairlike cells that allow mucus to cover frog skin. Instead, the independent cells used their cilia to move quickly — essentially using their genetic instructions for another purpose. The cells even responded to one another.

The team has been looking at ways to create and direct “xenobots,” tiny living robots that do particular tasks. In the past, they were successfully able to use the frog skin cells to shape little multicellular beings with the help of a complex computer algorithm. But these xenobots grew themselves from single cells. The research is upending biological convention, writes Philip Ball in an engaging profile of the biologists and their work in Quanta Magazine. “The results seem to imply that individual cells have a kind of decision-making capacity that creates a palette of possible bodies they could build — constrained and guided by the genome but not defined by it.”

One day, swarms of tiny xenobots could be used in potential medical therapies or environmental applications. The research also might shed new light on how multicellular organisms arose in the first place.

It’s heady work, but the possibilities are exhilarating — even as they challenge what scientists think they know about how cells use their genetic programming.