Intestinal stem cells (ISCs) in the gut of the fruit fly, Drosophila melanogaster, directly determine the fate of their daughter cells. The signaling protein called Delta, seen here in red, determines what type of cell the ISCs will produce. Large amounts of Delta signal the daughter cells to become gut-lining enterocytes (left panel), while small amounts of Delta signal them to become hormone-generating enteroendocrine cells (right panel).		Mutations that disrupt the Delta protein can cause ISCs to produce many tumor cells (thin arrow, bottom) as well as a few normal enterocytes (thick arrow, top).
(Images used with permission of the American Association for the Advancement of Science, Science, February 16, 2007; click images for higher resolution versions.) News Release