A sphere of cells that blossoms from only one stem cell can implant in a mouse uterus and form multiple tissues.

A single stem cell has been coaxed into forming a ball of cells that can implant in a mouse’s uterus, where it then generates all three founding tissues needed to build a foetus.

A mammalian embryo develops from a simple complex of cells called a blastocyst. In previous experiments, researchers combined two types of stem cells to create a blastocyst-like structure. But these did not develop well in culture.

Juan Carlos Izpisua Belmonte at The Salk Institute for Biological Studies in La Jolla, California, Jun Wu at the University of Texas Southwestern Medical Center in Dallas, and their colleagues instead searched for growth conditions that would enable a single type of stem cell to generate all three cell types present in a mature blastocyst. The team identified a way to transform stem cells into structures that looked and behaved like blastocysts.

These structures followed the characteristic stages of embryo development, even when grown in culture, and could implant and grow within the mouse uterus — whether the stem cells were generated from embryos or adult cells.