After that period, when the axons would normally have left the floor plate, the axons developed an additional need for neurotrophins to continue to grow. To learn whether the nerve cell axons needed to approach the floor plate cells to survive, Wang and Tessier-Lavigne grew nerve cells and floor plate cells in the same culture dish, but on opposite sides of a collagen gel. This gel physically separated the two types of cells, but allowed growth factors to pass readily from one cell type to the other. The experiments revealed that the nerve cells survived only if their axons grew near the floor plate cells. His team also found evidence that the tip of the growing axon senses this survival protein and sends a signal back to the main nerve cell body to thwart the suicide program.
Experiments are underway to isolate the survival signals.