Magic embryology: how the placenta appears (Introduction)

by David Turell , Thursday, October 01, 2020, 21:19 (1514 days ago) @ Balance_Maintained

Certain cells from the original fertilized egg form the placenta:

https://science.sciencemag.org/content/370/6512/19

"The placenta—a Frisbee-size hunk of tissue that chaperones a fetus in the uterus only to be tossed aside in the delivery room—has mysterious beginnings. The organ emerges from cells that develop alongside the embryo, and that have been difficult to grow in the lab. Now, researchers have devised a way to derive and observe early precursors of placental cells in a dish. They have found a method of “reprogramming” adult cells, reverting them to a primitive state, that can prompt them to become trophoblast stem cells (TSCs), which give rise to placental cells.

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"Those steps begin just days after a sperm and egg join. “The first decision in human life is to set aside the placental, supportive cells,” says Kathy Niakan, a developmental biologist at the Francis Crick Institute, whose team reported key molecular signals for that initial step in Nature last week. These cells go on to form the trophoblast, a multilayered ring that surrounds the embryo and helps it implant into the wall of the uterus. Some of these cells, TSCs, then give rise to cell types that will make up the bulk of the placenta, which enables mother and fetus to exchange nutrients and gases and helps protect the fetus from the mother's immune system.

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"Polo's team reported that these induced TSCs could develop into two major types of trophoblast cells and, like the cells surrounding an embryo, secrete human chorionic gonadotropin, a hormone whose signals are key to maintaining a pregnancy. David, a co-author on that paper, separately used gene expression data from human embryos to estimate that his own group's lab-derived TSCs are equivalent to those seen 8 to 10 days after fertilization, the team reported on 15 September in a preprint on bioRxiv."

Comment: Still not completely understood, but a highly complex process. Live birth requires this arrangement as there is no feeding yolk for food supply. The m other has to be the supplier. The placenta itself is very complex in its parts and actions. This had to be designed.