The primitive streak is a transient structure whose formation, on day 15 of human development, marks the start of gastrulation, the process in which the inner cell mass in converted into the trilaminar embryonic disc, which is comprised of the three germ layers (ectoderm, mesoderm and endoderm). At the end of the embryo formation, where is the primitive streak site? Is it possible that the primitive streak cells are stem cells?
The primitive streak starts at the posterior end of the embryo in response to signals form the extraembryonic endoderm and then extends toward the anterior about halfaway. It does not go into the prospective head region. The cells that migrate thorugh the streak are stem cells of the epiblast, an epithelial sheet derived from the inner cell mass of the blastocyst. The cells of the epiblast are stem cells in that they are still pluripotent. However, once cells migrate through the streak and become mesendoderm or ectoderm they are no longer stem cells. The anterior end of the streak is called the node and it will regress back to the posterior pole. As the primitive streak regresses it lays down the notochord which signals to mesoderm and ectoderm to establish Dorsal-ventral polarity. This is hard to visualize in 2 dimensions but a modern embryology book should cover this process.
- Badges
- Science topic
- Similar topics
- Biological Science
- Zoology
- Ornithology