![]() ![]() “This is an animal that, through evolution, has already solved the regeneration problem,” says Wagner. From a single transplanted cell, the host not only regained the ability to regenerate, but was also converted to the genetic identity of the donor strain.īecause this work showed that cNeoblasts can differentiate into diverse tissue types and even replace all of the tissues in a host planarian, the researchers were able to conclude that cNeoblasts are pluripotent stem cells.įurther study of cNeoblasts could help researchers understand how stem cells can act to promote regeneration. Because the donor cells were distinguishable from the host, the researchers demonstrated that the transplanted cNeoblast multiplied, differentiated, and ultimately replaced all the host’s tissues. Using another method, Wang and Reddien transplanted single cNeoblasts from one strain of planarian into lethally irradiated host planarians from a different strain, which lacked their own neoblasts and the ability to regenerate. Furthermore, Wagner showed that small numbers of cNeoblasts were capable of restoring regenerative potential to entire animals. Wagner analyzed the colonies and found that they contained cells differentiating into neurons and intestinal cells, indicating broad developmental potential for the initiating cNeoblast. By labeling cells for a gene expressed only in neoblasts, Wagner observed that these individual surviving cNeoblasts divided to form large colonies of cells. In one method, Wagner gave planarians a dose of radiation that killed all of their dividing cells, except for rare, isolated cNeoblasts. Their results are published in the May 13 issue of Science. Using complementary methods, Dan Wagner, Irving Wang-two graduate students in the Reddien lab and co-first authors-and Reddien have demonstrated that adult planarians not only possess pluripotent stem cells-known as clonogenic neoblasts (cNeoblasts)-but that a single such cell is capable of regenerating an entire animal. “The reason it’s never been possible to address this question is because we needed assays that allow us to ask what the regenerative potential of single cells is.” “And that question is at the heart of understanding regeneration in these animals,” says Whitehead Member Peter Reddien, who is also an associate professor of biology at MIT and a Howard Hughes Medical Institute (HHMI) Early Career Scientist. Until now, however, scientists could not determine whether neoblasts represent a mixture of specialized stem cells that each regenerates specific tissues or are themselves pluripotent and able to regenerate all tissues. In the planarian flatworm Schmidtea mediterranea, certain dividing cells, called neoblasts, have long been identified as essential for the regeneration that repairs the worm’s tissues. In humans, only embryonic stem cells and germ cells are pluripotent-with the ability to create all cell types in the body. In humans, we have blood stem cells in our bone marrow that make blood and immune cells, skin stem cells that produce new layers of skin, and intestinal stem cells that continually renew our gut linings, to name just a few. Most advanced animals, including mammals, have a system of specialized stem cells. In the case of the planarian flatworm, Whitehead Institute researchers have determined that the source of this animal’s extraordinary regenerative powers is a single, pluripotent cell type. CAMBRIDGE, Mass.– Ever since animals, such as lizards and starfish, were observed regenerating missing body parts, people have wondered where the new tissues come from. ![]()
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