Nine-day-old human embryo cultured in vitro: A clue to the origins of embryonic stem cells

Abstract

The aims of this study were to investigate whether the human embryo could sustain development beyond the blastocyst stage in vitro and to identify the precise origins of embryonic stem cells (ES cells) from the embryoblast. A frozen-thawed 4-cell embryo was cultured to the post-blastocyst stage. This 9-day-old embryo presented a solid mass of inner cells (resembling a tumour) surrounded by surface trophoblast cells. Clumps of multinucleated syncytiotrophoblast cells were evident at one pole. Most cells resembled those of blastocysts. However, there were groups of comparatively undifferentiated cells within the inner cell mass somewhat resembling ES cells documented previously, that might give a clue as to their origins. The embryo attempted to form an amnion with a cavity, but did not present a bilaminar, discoidal structure as expected in week 2 of development, and hence was abnormal.