Smedwi-2 belongs to the Argonaute/PIWI protein family and is most similar to PIWI proteins found in fruit flies. According to Sánchez Alvarado, PIWI proteins have been shown to play a role in regulating stem cells in plants and fruit flies, as well as humans. "This encompasses millions of years of evolution," he said. "Still, we don't know exactly how this particular gene is doing its function in any of these organisms."
To find out, the scientists used a technique known as RNA interference to specifically turn off the piwi gene in planaria. When they did this, they found that worms had the same defects as those whose neoblasts have been destroyed by radiation -- head regression, curling, and the inability to regenerate -- suggesting that the gene was needed for normal neoblast function.
The researchers examined piwi's role more closely, and found that when they amputated part of a worm where the gene had been turned off, the stem cells were still able to detect the wound. Amputation triggered the stem cells to divide, as in normal worms, and the daughter cells traveled proficiently to the part of the body where they were needed. However, once they arrived, they failed to replace the lost tissue.
When neoblasts divide, they produce at least two cell types ?one copy of the original, and one cell that can develop into a specialized cell to replace a lost cell elsewhere in the body. The researchers found that without piwi, the daughter cells from this division failed to differentiate into a specialized cell once they'd reached their destination. Based on their findings, Sánchez Alvarado said, "We think that piwi is actually involved in producing daughter cells that are competent to restore aged differentiated cells during homeostasis as well as missing tissues after amputation. Unlike what's been thou
Source:Howard Hughes Medical Institute