This is the world's first synthetic embryo complete with beating heart and brain beginning—no sperm or egg required

Israeli researchers have generated the first synthetic embryo without sperm, egg, or a womb, starting with mouse stem cells in a petri dish. By the eighth day, the heart was beating, blood was circulating, an intestinal track had formed, and there was a progenitor to a brain. The scientists at Israel's Weizmann Institute published their results in the journal Cell. From The Guardian:

Known as synthetic embryos because they are created without fertilised eggs, the living structures are expected, in the near term, to drive deeper understanding of how organs and tissues form during the development of natural embryos.

But researchers believe the work could also reduce animal experimentation and ultimately pave the way for new sources of cells and tissues for human transplantation[…]

While most of the stem cells failed to form embryo-like structures, about 0.5% combined into little balls that grew distinct tissues and organs. When compared with natural mouse embryos, the synthetic embryos were 95% the same in terms of their internal structure and the genetic profiles of the cells. As far as the scientists could tell, the organs that formed were functional.

[Research head Jacob] Hanna said synthetic embryos were not "real" embryos and did not have the potential to develop into live animals, or at least they hadn't when they had been transplanted into the wombs of female mice. He has founded a company called Renewal Bio that aims to grow human synthetic embryos to provide tissues and cells for medical conditions.