An anonymous reader quotes a report from the BBC: Scientists have grown an entity that closely resembles an early human embryo, without using sperm, eggs or a womb. The Weizmann Institute team say their “embryo model”, made using stem cells, looks like a textbook example of a real 14-day-old embryo. It even released hormones that turned a pregnancy test positive in the lab. The ambition for embryo models is to provide an ethical way of understanding the earliest moments of our lives. This research, published in the journal Nature, is described by the Israeli team as the first “complete” embryo model for mimicking all the key structures that emerge in the early embryo.
Instead of a sperm and egg, the starting material was naive stem cells which were reprogrammed to gain the potential to become any type of tissue in the body. Chemicals were then used to coax these stem cells into becoming four types of cell found in the earliest stages of the human embryo: epiblast cells, which become the embryo proper (or foetus); trophoblast cells, which become the placenta; hypoblast cells, which become the supportive yolk sac; and extraembryonic mesoderm cells. A total of 120 of these cells were mixed in a precise ratio — and then, the scientists step back and watch.
About 1% of the mixture began the journey of spontaneously assembling themselves into a structure that resembles, but is not identical to, a human embryo. The embryo models were allowed to grow and develop until they were comparable to an embryo 14 days after fertilization. In many countries, this is the legal cut-off for normal embryo research. The hope is embryo models can help scientists explain how different types of cell emerge, witness the earliest steps in building the body’s organs or understand inherited or genetic diseases. Already, this study shows other parts of the embryo will not form unless the early placenta cells can surround it. There is even talk of improving in vitro fertilization (IVF) success rates by helping to understand why some embryos fail or using the models to test whether medicines are safe during pregnancy.