A 3-D image stack, visualized by confocal microscopy, of a five-day-old human embryoid, made up of squamous amnion cells (green) and pluripotent cells (pink). Blue denotes nuclei.UNIVERSITY OF MICHIGANUsing human pluripotent stem cells and 3-D media, scientists have sparked the growth of an amniotic sac-like structure—“a hollow cyst, which contains a cavity (a lumen) that is enveloped by a layer of cells,” describes lead author Yue Shao in an email to The Scientist. They’ve dubbed it a post-implantation amniotic sac embryoid, PASE for short.

See Y. Shao et al., “A pluripotent stem cell-based model for post-implantation human amniotic sac development,” Nature Communications8:208, 2017.