The replacement of tissue lost to injury or shed during the body's normal activities is essential for the survival of most organisms. The new study, published in the November 25, 2005, issue of the journal Science, helps scientists understand how stem cells make this process possible. The research, performed at the University of Utah School of Medicine, was carried out by Helen Hay Whitney postdoctoral fellow Peter W. Reddien (now an Associate Member at the Whitehead Institute for Biomedical Research), and led by Howard Hughes Medical Institute investigator Alejandro Sánchez Alvarado.
Salamanders, zebrafish, and other organisms are capable of regenerating entirely new body parts. Although the human body does not face such demands, it is constantly replacing lost cells. For example, blood replenishes itself, wounds heal, and the lining of the gut sloughs off and is restored. Nowhere, however, is the process of regeneration more dramatic than in the freshwater flatworm planaria. Cut one of these animals in half, and a week later, two fully functional worms will have developed from the pieces. Cut a piece that is 1/279th the size of the animal, and it too will regrow into a complete worm.
The process, scientists know, is dependent on stem cells in the adult planaria known as neoblasts. Like all stem cells, neoblasts have the capability to develop into a variety of different cell types, meaning they can transform themselves into whatever tissue is needed after injury, be it intestine, skin, or brain. Even in the absence of injury, these cells are critical to maintain a healthy worm, as t
Source:Howard Hughes Medical Institute