At least it can be said that planeists have extraordinary talents. If one of the flatworms is cut in half, the two halves will grow back, giving you two identical worms. Cut the flatworm’s head in half and it will grow two heads. Cut the flatworm’s eyes and it will grow back. Staring at a flatworm without eyes-it will take root. If there is time, fragments as small as one-half to 279 of a flatworm will become new, complete flatworms.
This regeneration process has fascinated scientists for more than 200 years, prompting people to perform countless funny performances (if some creepy) to understand how complex creatures rebuild themselves over and over again. In a paper published in the journal Science on Friday, the researchers revealed a tantalizing glimpse of how the worm̵
Scientists report that specialized cells provide directions for neurons extending from the newborn eye to the worm’s brain, thereby helping them connect properly. Studies have shown that the cell guide hidden in the entire planeworm may allow the worm’s new growth neurons to track its pace. Collecting these and other insights from the study of flat worms may one day help scientists interested in helping humans regenerate injured neurons.
Researcher Maria Lucila Scimone of the Whitehead Institute of Biomedicine at the Massachusetts Institute of Technology discovered these cells while studying Schmidtea Mediterraterranea, a common planarian of freshwater plants in southern Europe and North Africa. In another experiment, she pointed out that they are expressing genes involved in regeneration.
Peter Reddien, a professor of biology at the Massachusetts Institute of Technology, said: “In every animal she looks at, she sees only a few of them.” She is also the author of the paper.
The team looked more closely and found that some cells related to regeneration are located at the key branch points of the neural network between the worm’s eyes and brain. When the researchers transplanted one animal’s eye into another, neurons growing from the new eye always grew toward these cells. When nerve cells reach their target, they continue to grow along the path that brought them to the brain. Removing these cells means that the neurons are lost and have not reached the brain.
These cells seem to be acting as a kind of guide. Dr. Redion said that signpost cells pointing to other cells play an important role in the embryonic development of many organisms. But by the time most animals reach adulthood, these cells usually disappear.
However, in flatworms, there are obviously adults with cells that perform this guiding role. Dr. Redion said they might use signals from muscle cells to arrange themselves along the route from the eye to the brain and tell them exactly where they should be in the body.
For a long time, scientists and doctors have placed high hopes on the regeneration ability of flat worms-not only to cultivate a new head, but to cure spinal cord injuries and other serious injuries. However, letting the right cells grow to replace the lost cells is only part of the process.
Dr. Redion said: “One thing we realized in this work is that the rewiring challenge can be a big challenge.” Ensuring that the transplanted neurons are properly connected may be another important step.
Among flatworms, Dr. Redion and his colleagues are planning to continue to look for cells that can provide guidance for regenerative neurons.
“Are there signpost-like cells elsewhere in the nervous system?” he asked. Maybe the nervous system is full of tiny road signs everywhere, showing the way to the brain.