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Scientists from the Hebrew University have shown for the first time how embryos develop their shape

The researchers repeated Schaffman and Mangold's experiment with the aim of verifying that the cells produced from embryonic stem cells do possess organizational abilities, but this time the human cells, and not those of the amphibian, were implanted into the frog embryo.

Human stem cells take the form of an embryo. Illustration: Nadav Sharon
Human stem cells take the form of an embryo. Illustration: Nadav Sharon

 Is it possible that a cluster of cells the size of a disc turns into a fetus during the first month of pregnancy? Since the dawn of history, humans have been trying to remove the mystery from the mechanism that gives the human embryo its external form.

The first significant step in understanding the subject was made nearly a century ago in experiments conducted by the German researchers Hans Schaffman and Hilda Mangold. The two identified in the embryos of a newt, an amphibian close to the salamander, a group of cells that, following their implantation, created a newt with two heads. In order to try to understand why this happened, the two conducted studies from which they concluded that the transplanted cells organized the environment in which they were found and turned it into a typical embryo shape. Therefore, the researchers named these cells "organizing cells". The newt embryo possessed both its organizing cells and the transplanted cells, and both organized the surrounding cells into a head structure.

Recently, PhD student Nadav Sharon - under the guidance of Prof. Nissim Benvanisti from the Institute of Life Sciences at the Hebrew University and in collaboration with Prof. Avraham Feinsud from the School of Medicine of the Hebrew University and Hadassah - succeeded in creating organizing cells using human embryonic stem cells. Based on the similarities in the early stages of the development process among all vertebrates, the team grew the human cells under conditions similar to those of amphibian embryos. Within two days the human cells began to express genetic characteristics of the organizing cells.

The researchers repeated Schaffman and Mangold's experiment with the aim of verifying that the cells produced from embryonic stem cells do possess organizational abilities, but this time the human cells, and not those of the amphibian, were implanted into the frog embryo.

The midline of the amphibian embryo is marked by a neural tube. This is a tissue designed to develop the central nervous system. To the astonishment of the team, some of the frog embryos in which human cells were transplanted developed two neural tubes instead of one. "The second tube was composed of frog cells, which proves that the injection of human cells caused the cells in the environment to organize into the shape of a tube," Sharon explains the findings of the study published in the latest issue of the journal  Stem Cells. Cells..

According to Sharon, "The process of defining the shape during the development of the fetus is a particularly important process, during which any deviation could lead to a miscarriage or the birth of a damaged baby. The identification of the organizing cells should allow a better understanding of the process." Sharon also says: "The ability of human organelle cells to shape the neural tube of a frog may help in the development of human neural tubes in cultures. From these tubes it will be possible to take nerve cells for transplantation in people with spinal cord damage, although additional research must be conducted in order for us to reach this stage."

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