The new study began with an insight stemming from years of work on a different flatworm, the planarian, in Newmark's lab. Collins thought that schistosomes might make use of the same kinds of stem cells (called neoblasts in planarians) that allow planarians to regenerate new body parts and organs from even tiny fragments of living tissue.
"It just stood to reason that since schistosomes, like planaria, live so long that they must have a comparable type of system," Collins said. "And since these flatworms are related, it made sense that they would have similar types of cells. But it had never been shown."
In a series of experiments, Collins found that the schistosomes were loaded with proliferating cells that looked and behaved like planarian neoblasts, the cells that give them their amazing powers of regeneration. Like neoblasts, the undifferentiated cells in the schistosomes lived in the mesenchyme, a kind of loose connective tissue that surrounds the organs. And like neoblasts, these cells duplicated their DNA and divided to form two "daughter" cells, one of which copied its DNA again, a process that normally precedes cell division.
"Stem cells do two things," Newmark said. "They divide to make more stem cells and they give rise to cells that can differentiate."
Collins had labeled the cells with fluorescent markers. This allowed him to watch how they behaved. He noted that over the course of a few days, some of the labeled cells migrated into the gut or muscle, to become part of those tissues.
"We label the cells when they're born and then we see what they grow up to become," Collins said. "This is not conclusive evidence that these cells are equivalent to the planarian neoblasts, but it is consistent with the hypothesis that they are."
|Contact: Diana Yates|
University of Illinois at Urbana-Champaign