Development: Human stem cells get organized

The organizer, a long-theorized cluster of cells that helps organize and direct embryonic development, has been demonstrated to be present in human tissue for the first time, reports a paper published online this week in Nature. The study provides a new model for early embryonic development and suggests that the organizer is highly conserved across the animal kingdom.

In 1924, Hans Spemann and Hilde Mangold performed what has become arguably one of the most famous experiments in developmental biology. They grafted a tiny piece of tissue from one salamander embryo into another salamander embryo and showed that it induced the host cells to form a second embryo. They called the grafted region the organizer, because it could organize the host cells around it.

In the new study, Ali Brivanlou and colleagues grew human embryonic stem cells on special microprinted disks and treated them with growth factors, which induced them to form organizer-like tissue. This cluster of cells was then grafted into chicken embryos, where it induced the surrounding host cells to form elongated neural tissue, demonstrating its organizational capacity. By using human stem cells to obtain a tissue displaying organizer properties, the authors have established a system that should enable further understanding of the workings of these cells.