The study of embryonic development is a complex and tightly regulated field. By influencing a process that regulates gene expression, researchers at the Institut Pasteur have succeeded in recreating in vitro mouse cell clusters that mimic in some respects the structure of real embryos. By avoiding the manipulation of embryos, these approaches pave the way for applications such as the study of cancers, congenital diseases and infertility, and could provide a source of tissue for regenerative medicine.