Scientists have been making spectacular strides with stem cell research and are getting ever closer to creating replacement organs for patients who need them due to disease or injury. A group of researchers led by Christine and Bernard Thisse from the University of Virginia School of Medicine have made a colossal step forward by actually stimulating embryonicstem cells to form a fish embryo. The results of the research were published in Science.

So how many signals were needed to spark the cellular processes needed for stem cells to begin forming a zebrafish embryo? Ten? Twenty? Surprisingly, just two. The team subjected the cells to opposing gradients of the growth factor family members Nodal and bone morphogenetic protein (BMP). After receiving the signal, the cells were induced into embryonic development and were then able to organize into an embryo.

This gives scientists and unprecedented amount of control over the fish’s embryonic development. By regulating the concentration and location of developmental signals, the team has made embryos that reach full size in 24 hours. This also allows them to target the growth of specific organs and tissues.

Understanding how to better control the stem cells will give researchers an easier time in future studies, because this is effectively starting down the road to unleashing the stem cell’s true potential. “If we know how to instruct embryonic cells,” Christine said in a press release, “we can pretty much do what we want.”

Next, the team will attempt to create the same results in mice. Though the animals are more complex than zebrafish, the Thisse lab expects that the signaling procedures will be fairly similar. Eventually, they hope to use human cells to create specific tissues and organs.

Creating a tailor-made replacement organ eliminates the possibility of rejection. Each year in the United States, over 28,000 people will have an organ transplanted. It isn’t remotely enough, as another name gets added to the wait list every 11 minutes, and 18 people die each day waiting for the live-saving call that never comes.