Amniotic fluid may act as a transporting pathway for signaling molecules and stem cells during the embryonic development of amniotes.

Amniotic fluid (AF) is formed at the very early stages of pregnancy, and is present throughout embryonic development of amniotes. It is well-known that AF provides a protective sac around the fetus that allows fetal movement and growth, and prevents mechanical and thermal shock. However, a growing body of evidence has shown that AF contains a number of proteins and peptides, including growth factors and cytokines, which potently affect cellular growth and proliferation. In addition, pluripotent stem cells have recently been identified in AF. Herein, this article reviews the biological properties of AF during embryonic development and speculates that AF may act as a transporting pathway for signaling molecules and stem cells during amniote embryonic development. Defining this novel function of AF is potentially significant for further understanding embryonic development and regenerative medicine, preventing genetic diseases, and developing therapeutic options for human malignancies.