What the Humble Planarian Teaches Us About the Building Blocks of Life

At first glance, planarians are not really impressive. These brownish flatworms, each less than half an inch long, have few distinguishing features: at one end, a tail ends in a rounded tip; at the other, a head punctuated by a pair of large cartoonish eyes.

As mundane as worms may seem, however, they have a capability we can only dream of. Cut off the head of a planaria and it will grow a new one. Cut off his tail and he will soon be replaced. Even tearing his body into small pieces is okay. Each piece, growing back from its injured edges, replaces nerves, muscles and other tissues until it becomes an individual, fully formed worm in just a few weeks.

“One of the big questions we want to answer is How? ‘Or’ What it does it at the genetic level,” says Bo Wang, assistant professor of bioengineering at Stanford. “What is it in the worm’s DNA that allows it to choose which parts of the body to grow, how much they will grow, where to stop and when to stop?”

Wang studies extraterrestrial planarian regeneration. Part of what drives this amazing ability, he says, is the fact that the worms’ bodies are filled with pluripotent stem cells, a “universal” cell type that can grow into any type of tissue. When a worm is cut in half, biochemical signals radiate outward from the damaged site, setting these stem cells into action. Gradually, the cells differentiate into muscles, nerves and other structures, forming a new head or tail over several days.

Although this type of research is his main focus today, Wang says he never expected to find himself in the field. Originally trained as a physicist, he spent much of his early career studying Brownian motion, the random motion of tiny particles suspended in liquid or gas. Then, by chance, he saw a video of the worm C.elegans developing from a fertilized egg.

“As a physicist, I thought that when it came to things on the microscopic scale, all movement had to be random, powered by heat energy and probability, but the cells in these worm embryos could divide and move synchronously in a programmed way even though they were only a few microns in size,” he says. “That blew my mind. I think that’s what really made me go from working on physics to working on biology.

Today, Wang explores some of the most fundamental building blocks of life: the different types of cells that make up an organism. His lab sequences DNA and messenger RNA, the linear molecules that guide protein synthesis, in the individual cells of several animals, including planarians, and develops computational methods to compare them to cell types in other animals. animals ranging from sponge to human in order to find commonalities and differences.

In the process, they learn how each of these organisms developed unique and powerful ways to use conserved cell types to build new structures and invented new cell types to survive in their environment.

However, Wang does not want to stop at cataloging these types of cells. It aims for more ambitious goals. With a better understanding of how cell types make tissue and how DNA in a cell nucleus controls that cell’s fate and identity, he says, it may one day be possible. to harness the power of biology for our own ends.

“As a bioengineer, I constantly think about this. Once we know the new functions of a piece of DNA, we can transfer them to other cells. It’s really about transferring the knowledge that we get from one system to another,” he says. “I think we could eventually use them to program ‘living machines’ that do a specific job.”

It’s not that far-fetched. New technologies developed over the past decade make it easier than ever to manipulate DNA and insert it into a living cell. Biologists do this every day with microbes and human cell lines, reprogramming them into tiny “factories” that spit out drugs or other products. In theory, the construction of entirely new cells, or even new organisms, in the laboratory could be imminent. Wang thinks it’s just a matter of imagination.

“We don’t really know what the possibilities are for us yet,” he says. “But that’s the most exciting part of being a scientist. We are constantly on the lookout for novelties, new surprises. It’s what gets me up every day.