The Worm Has Turned

New research uncovers processes driving planarian stem cell differentiation in living tissues.

Planaria are tiny (about the size of a toenail clipping) aquatic flatworms, most often found in standing water. Though humble in size and appearance, they are one of nature's wonders. Planaria have the ability to regenerate from a small scrap of tissue, and have an abundance of adult stem cells, called neoblasts, that can specialize, or differentiate, into other cell types. Two studies from the Sánchez Alvarado Lab shed light on some of the intricate processes at work when planarian neoblasts differentiate into skin cells.

In one study, the researchers identified how the enzyme MLL1/2 affects the development of planarian cilia, the microscopic, hairlike structures on the organism's skin that help it swim. Without the enzyme, planaria lose their cilia and stop swimming. The discovery suggests that defects in the process of building cilia may begin earlier than thought, a finding that has potential implications for the detection of a broad range of human health conditions.

The other study found that a gene called egr-5 is important and plays a key role in helping neoblasts differentiate into skin cells. When the activity of egr-5 was reduced, it blocked neoblast daughter cells from differentiating properly, and they did not make mature skin cells. The findings uncover the critical role of egr-5 in the development of skin cells, and illustrate the complexity of this seemingly simple organism.

These studies were published respectively in the December 2015 online issue of Cell Reports and the October 2015 issue of the online journal eLife.