Abstract
The growth factors that drive the division and differentiation of stem cells during early human embryogenesis are unknown. The secretion of endorphins, progesterone (P(4)), human chorionic gonadotropin, 17beta-estradiol, and gonadotropin-releasing hormone by trophoblasts that lie adjacent to the embryoblast in the blastocyst suggests that these pregnancy-associated factors may directly signal the growth and development of the embryoblast. To test this hypothesis, we treated embryoblast-derived human embryonic stem cells (hESCs) with ICI 174,864, a delta-opioid receptor antagonist, and RU-486 (mifepristone), a P(4) receptor competitive antagonist. Both antagonists potently inhibited the differentiation of hESC into embryoid bodies, an in vitro structure akin to the blastocyst containing all three germ layers. Furthermore, these agents prevented the differentiation of hESC aggregates into columnar neuroectodermal cells and their organization into neural tube-like rosettes as determined morphologically. Immunoblot analyses confirmed the obligatory role of these hormones; both antagonists inhibited nestin expression, an early marker of neural precursor cells normally detected during rosette formation. Conversely, addition of P(4) to hESC aggregates induced nestin expression and the formation of neuroectodermal rosettes. These results demonstrate that trophoblast-associated hormones induce blastulation and neurulation during early human embryogenesis.