Cell potency
Cell potency refers to a cell's ability to differentiate into various cell types, a critical concept in developmental biology and regenerative medicine. Stem cells, particularly embryonic stem cells, are central to this topic due to their diverse potencies, which include totipotent, pluripotent, and multipotent classifications. Totipotent cells are the most versatile, capable of developing into any cell type in an organism, as well as the extraembryonic tissues that form the placenta. As an embryo develops, totipotent cells give way to pluripotent cells, which can differentiate into nearly every cell type within the body but cannot form extraembryonic tissues. Multipotent cells, often found in adults, have a more limited potential and can specialize into specific cell types, such as those in blood or cartilage.
The ethical considerations surrounding the use of stem cells, particularly those derived from human embryos, have led to alternative approaches, such as the creation of induced pluripotent stem cells (iPSCs). These cells are generated by reprogramming adult cells to exhibit similar properties to pluripotent stem cells, thus offering a promising avenue for research and therapy without the ethical concerns associated with embryo destruction. Ongoing research aims to further understand and manipulate cell potency, potentially leading to innovative medical treatments and a deeper understanding of cellular development.
On this Page
Cell potency
Cell potency is a cell’s ability to transform into different types of cells. Stem cells, and particularly embryonic stem cells, are important to scientific research and medicine because of their unique cell potency. Some stem cell potencies include totipotent, pluripotent, and multipotent. These various types of stem cells are created at different phases of an organism’s life cycle. The most potent cells are created first. Scientists and medical professionals use various cells for different applications, depending on their potencies. Scientists have even discovered ways of manipulating other cells to change their potencies. Scientists hope to use these altered cells in their research and in medical procedures to help avoid ethical concerns people have about using cells from human embryos.
Background
Cells are the building blocks of all living things, and all living things are made up of one or more cells. Furthermore, all cells are generated from other cells. Many of the specialized cells in adult human bodies are made from the same type of cells. For example, the cells of epidermis (skin) in an adult human produce new skin cells. Yet, the first cells that are created in a human embryo must have the ability to create every other type of cell in the body. Cells that can create many other types of cells have a unique potency.
In humans and many other types of mammals, a new organism is created when an egg cell is fertilized by a sperm. This forms a zygote, which is made of one cell. The zygote then undergoes rapid cell division to create a blastula. The blastula will eventually become an embryo. Although embryos are essentially groups of cells, they are specific and organized groups of cells. These groups of cells will eventually turn into an adult human if they experience the right conditions. Adult humans have hundreds of different types of cells, including neural cells, muscle cells, and skin cells. All the different types of cells eventually form inside embryos, but a blastula, the very early form of the embryo, is made up of only unspecialized stem cells. The cells will go on to help form all the rest of the cells in the embryo. These early cells have to be able to create the hundreds of different types of cells that will later form. Therefore, the cells created early in the embryo’s lifecycle have to be able to make different types of cells. When one type of cell can create other types, it is totipotent, pluripotent, or multipotent.
Overview
Cells of different potencies form at different stages of an organism’s lifecycle. These different types of cells have different potencies. The first cell of a human is the zygote, or the fertilized egg. It is a totipotent cell. Totipotent cells form naturally only in embryos and are created just after an egg cell is fertilized by a sperm cell. After the zygote begins to divide to create more cells, a number of other totipotent cells form. These totipotent cells are the most potent types of cells in humans because they can produce any other type of cell. So, a totipotent can produce a human stem cell, a human skin cell, or a human muscle cell, among others. Totipotent cells are the most potent cells because they can create every type of embryonic cell, and they can also create extraembryonic cells. Extraembryonic cells make up the placenta, which is the organ that develops alongside an embryo and supports it by providing oxygen and nutrients and by ridding it of waste.
A human blastula creates cells with total potential, or totipotent cells, for about four days. Then, the blastula changes slightly so that the cells produced are no longer totipotent. Some researchers believe that a type of microRNA plays a role in ending the production of totipotent cells. MicroRNA is a small, noncoding form of RNA that is present in all cells and helps in carrying out instructions from a cell’s DNA. This microRNA stops new cells from being able to produce the extraembryonic tissues. This changes newly formed cells from being totipotent to being pluripotent cells.
Pluripotent cells are also embryonic stem cells. Pluripotent cells are created in early embryos, but they are created after totipotent cells. Pluripotent embryonic cells can turn into any other types of cells that make up the body. So, they can make any embryonic cells. They cannot, however, create extraembryonic cells that will eventually become the placenta. The pluripotent stem cells have the potential to be all other types of cells, though.
As an early embryo develops, it will generate thousands of pluripotent stem cells. Then cell differentiation will begin at about three weeks of development. Cellular differentiation happens when the unspecialized cells of the embryo begin to specialize. At this time, the embryo begins to produce the differentiated cells that will go on to form specific parts of the body, such as skin cells and muscle cells. Even when cells begin to specialize, however, the embryo will continue to make some cells that are unspecialized. They are called multipotent cells.
Multipotent cells are also cells that can change into different types. However, they are more limited than pluripotent cells. One of the most common types of multipotent cells are adult stem cells. The human body continues to produce unspecialized cells throughout the human lifecycle. However, these unspecialized cells are not as free as pluripotent cells to become any other type of cell in the body. Multipotent cells will specialize into a cell in a particular line. For example, adult humans create mesenchymal stem cells. These are multipotent cells generated in the bone marrow. These cells can then generate other types of cells, including cells that will make up the cartilage and cells that will make up parts of the skeletal system. In this case, the mesenchymal stem cells are unspecialized, but they are limited in the types of cells they can generate. Cord blood stem cells are another type of multipotent cells.
The unique potency of totipotent and pluripotent cells has made them popular among scientists for research and medical applications. Scientists can change these cells into other types of cells. They can study the functions and reactions of different cells using the same cell line. They can also, in some cases, use these stem cells to treat injury or disease. Although these cells are very useful, their use in labs and medicine is hotly debated because they must be harvested from embryos. When scientists use human embryos to harvest the cells, this destroys the embryos. Some people believe destroying human embryos is killing a person. The United States and countries around the world have different laws and regulations regarding harvesting and using stem cells because of these ethical concerns.
Although pluripotent cells are popular for research, some people object to their use because of ethical concerns. For this reason, some scientists have tried to generate pluripotent and totipotent cells from other cells. Scientists discovered in 2006 that they could manipulate some adult cells to change into cells that had the same properties as pluripotent stem cells. Scientists called these cells induced pluripotent stem cells (iPSCs). These cells are similar to stem cells because they can be changed into any number of specialized cells. So, scientists can use these to study different types of cells in the lab. Some medical professionals have also used iPSCs to treat medical conditions. The discovery of iPSC has dramatically changed stem cell research and debates about its ethics. Although iPSCs have not totally replaced pluripotent stem cells in science, they have changed the way many cell researchers do their work.
Scientists are also interested in creating cells that act like totipotent cells. Researchers from the University of California–Berkeley also claim to have developed cells that are similar to totipotent cells. These cells could generate all the types of cells inside the embryo, but they could also develop cells that would exchange nutrients between the mother and embryo. This unique characteristic made them similar to the totipotent rather than pluripotent cells. Although research with cells is in its early stages, the scientists who have made these discoveries planned to continue their research to develop cells with unique potency.
Bibliography
Condic, Maureen L. “Totipotency: What It Is and What It Is Not.” Stem Cells and Development, 2014, vol. 23, no. 8, pp. 796–812, doi: 10.1089/scd.2013.0364.
Hasuwa, Hidetoshi, et al. “Mobile Elements Control Stem Cell Potency.” Science, 10 Feb. 2017, vol. 355, no. 6325, pp. 581–582, doi: 10.1126/science.aam6589.
“How Does a Fertilized Egg Develop?” Nature, 14 June 2007, www.nature.com/articles/stemcells.2007.13. Accessed 7 Jan. 2020.
Macfarlan, T.S., et al. “Embryonic Stem Cell Potency Fluctuates with Endogenous Retrovirus Activity.” Nature, 2012, vol. 487, pp. 57–63, doi: 10.1038/nature11244.
Murnaghan, Ian “Totipotent Stem Cells.” Explore Stem Cells, 18 July 2019, www.explorestemcells.co.uk/totipotentstemcells.html. Accessed 7 Jan. 2020.
Salmikangas, Paula, et al. "Potency Testing of Cell and Gene Therapy Products." Frontiers in Medicine, 4 May 2023, doi.org/10.3389/fmed.2023.1190016. Accessed 7 Nov. 2024.
“Stem Cell Basics.” National Institutes of Health, stemcells.nih.gov/info/basics.htm. Accessed 7 Jan. 2020.
“Stem Cells: What They Are and What They Do.” Mayo Clinic, 8 June 2019, www.mayoclinic.org/tests-procedures/bone-marrow-transplant/in-depth/stem-cells/art-20048117. Accessed 7 Jan. 2020.
“What Is the Difference Between Totipotent, Pluripotent, and Multipotent?" NYSTEM New York State Stem Cell Science. stemcell.ny.gov/faqs/what-difference-between-totipotent-pluripotent-and-multipotent. Accessed 7 Jan. 2020.
“What Are Stem Cells?” Library of Congress, www.loc.gov/everyday-mysteries/item/what-are-stem-cells/. Accessed 7 Jan. 2020.