Stem cells were often thought of as the holy grail of biological discovery after they were uncovered by Ernest McCulloch and James Till in 1963. A method to produce cells that can form into any part of the body, potentially providing new organs and prevent horrible disorders like leukemia.
Of course, things didn’t really turn out like that. At least not at the time. It has been a slow, though steady, slog to progress the scientific literature toward workable uses of stem cells. With hiccups here and there, like the US stem cell research ban in 2001 that set back the field for about a decade.
But, over time, steps have been made. The ability to produce new copies of organs has improved tremendously and work on treating leukemia and other conditions, with the combined help of genetic engineering techniques, is finally beginning to work. There’s still quite a lot left to do though.
Time For Learning
Before discussing today’s new study, let’s first go over stem cells and the different types of them, along with what is desired by those in the scientific field. What is it that they want to achieve with future research?
Stem cells are often divided into different groups depending on their “potency”. Cell potency is a question of how many different cell types that that one cell can turn into. What is its potential to change?
The most basic and limited stem cells are referred to as oligopotent. They have only a small handful of possibilities. Lymphoid stem cells, for example, can turn into B, T, or natural killer cells, but not other blood cells. Myeloid stem cells can form other blood cell types such as some white blood cells, but not the three already listed. And both can’t turn into any other cell type outside of blood cells. They are limited.
The next step up from this are multipotent stem cells. They would include stem cells that can turn into any type of cell within a category. Haematopoietic stem cells, for instance, can form into basically any type of blood cell at all. Indeed, the term haematopoiesis refers to the formation of blood cell components.
Multipotent stem cells often lead to progenitor cells, those that have more options, but are still set up into discrete types. They are limited in how many times they can copy themselves and have a tendency to form into a particular cell in general. They are sometimes considered the same as stem cells, but there are a few differences, like those noted.
The Many Cells Potency
The next level is one that you are likely more familiar with: pluripotent stem cells or PSCs. These are the most commonly used type of stem cells in science, due to their capacity to form into any of the three primary germ cell layers after the zygote phase.
The endoderm layer of cells turns into the parts that make up the digestive tract and the lungs. The mesoderm forms the bones, muscles, and blood tissues. Finally, the ectoderm cells form the skin and the nervous system.
Even this category has different forms within it. Completely pluripotent stem cells are like embryonic stem cells (ESCs) and induced stem cells (iPSCs). They have the full ability to turn into basically any cell in the body. Then there are other types used in science like epiblast-derived stem cells (EpiSCs) that are limited by their morphology and cannot be used in things like chimera cell formations.
The All Potentcy
You might be wondering why, if pluripotent stem cells can form into any cell in the body, then how are they still limited? That’s because there are still other cells not necessarily a part of the body to consider. Also, pluripotent stem cells make up those embryonic stem cells inside of the zygote, but not the original cells prior to this in the form of the cellular mass called the morula.
There is still another part to consider, the extra-embryonic tissue. These are the materials that surround the embryo during its formation and growth. To use the example of an egg, this tissue would make up the egg white portion. This is the amniotic sac filled with amniotic fluid and the chorion membrane that forms the placenta. These tissues are still outside the range of pluripotent stem cells.
Which then brings us to our final level. The heights of potential cell differentiation is held by totipotent stem cells, those that make up the original egg and split cells that turn into the zygote. It is to reach this stage that so much work has gone into reverting adult cells back into embryonic form and unlocking true totipotency in them.
Creating New Potency
Now, finally, on to today’s study. Researchers at the Salk Institute in California and in collaboration with the Peking University in China have succeeded in developing a specialized chemical cocktail that is able to convert mouse and human stem cells that are being tested into forms that could make extra-embryonic tissue in addition to all the normal embryonic cells types.
It has been incredibly difficult in the past to get a hold of such totipotent cells for study, as obtaining embryonic stem cells directly often happens after zygote formation, meaning they no longer have their full capabilities. After fertilization, the division of the egg cell happens rather quickly and the cells turn into only those that will eventually form the extra-embryonic tissue and those that fill form the embryo, losing the cells that can form into either.
Fertilization And Organ Development
The scientists at the Salk Institute have decided to call these new cells Extended Pluripotent Stem cells or EPS cells for short. The hope is to be able to use these cells for early embryonic development research and to better improve in-vitro fertilization techniques.
They may also be useful in chimeric cell research for making organ replacements that aren’t rejected by the body and in transgenic gene editing cell transfers.
For now, they are going to work on creating a stable cell line of these totipotent cells so that enough will be available for research and development around the world.
Photo CCs: 1 msc DAPI+ThR001 a from Wikimedia Commons