Stem Cells — Reaching A Cell’s True Potential -

Philip Iannaccone
4 min readMay 10, 2018

A basketball-like embryo, a blastocyst, is put in a dish and it flattens out to a structure that looks like a fried egg. The big flat pavement stone like cells around the outside are cells from the outside of the blastocyst, called trophectoderm. The bright round clump in the middle are dividing inner cell mass cells, from which embryonic stem cells are derived.

May 5th, 2014:

Continuing from the last time we found that there is a population of cells in the very early embryo, the blastocyst, that gives rise to stem cells. These are cells that can be grown in a dish under the correct conditions, and have the ability (or potential) to both divide and produce more of themselves but also to turn into different kinds of cells. These stem cells have the potential to turn into almost any kind of cell we have in our bodies.

A blastocyst from a rat with large pavement stone-like trophectoderm on the outside and small round clumped inner cell mass cells on the inside.

The total diameter of the blastocyst is approximately 100µm, or about the width of a human hair.

This is because the stem cells grow from a population of cells in the blastocyst, called inner cell mass cells that give rise to all of the cells and tissue of the fetus during development in the uterus. The cells are produced by removing the blastocyst from the oviduct (the tube between the ovary and the uterus) and putting the blastocyst on to a layer of connective tissue type cells in a dish. The blastocyst flattens out with a lump or mound of cells from the inner cell mass on top giving the structure the appearance of a “fried egg” sunny side up! The “yolk” of this fried egg like structure (that consists of the dividing inner cell mass cells) is where the embryonic stem cells come from. They divide and spread in the dish. Special protein factors have to be added at this point in the process to prevent the stem cells from differentiating, that is, turning into different cell types.

Then the mound of cells must be broken up manually. They are so small this must be done under a microscope and requires a great deal of skill. The process has to be repeated many times before easier more commonly used methods for separating individual cells can be used successfully. This process is done to expand the number of stem cells. As one cell can turn into many, large numbers of cells can be obtained in this way. This is often referred to as “passaging the cells” or “expanding the cell culture.”

The bright round clump in the middle consistes of hundreds perhaps thousands of individual embryonic stem cells. They are small round cells that are almost all nucleus and about 10µm in diameter. Beneath the stem cells are support cells that help maintain the undifferentiated, pluripotent state of the stem cells.

Because they can divide indefinitely, one of the promises of stem cells is that large supplies of cells used in therapy could be easily made available. This has been done in mice and rats and a number of other species and eventually was done in humans as well.

Since an embryo had to be placed in a dish before implantation for this to work, scientists at Johns Hopkins University and the University of Wisconsin had to work diligently on the ethics of the methods used. While the inner cell mass cells of the embryo survive this process the embryo itself cannot go on to make a person in its own right. Now there is a strict control and regulation system in place at the National Institutes of Health to ensure that the existing embryonic stem cells used for trials were derived under the highest ethical regimes.

New methods will be discussed in upcoming posts that allow for some of the ethical dilemma to be put behind us. We will discuss the origins of those methods next.

To recap we suggest you watch this video from TEDEd:

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Philip Iannaccone

Phil Iannaccone is a Professor of Pediatrics and Pathology at Northwestern University Feinberg School of Medicine.