![]() It was possible to have cell types for testing new therapeutics and perhaps even new transplantation methods that were previously not possible. For the first time, scientists could, in theory, generate all the building blocks of our body in unlimited amounts. The desire to use stem cells’ unique properties in medicine was greatly intensified when James Thomson and collaborators first isolated ES cells from human blastocysts. ![]() This means that when the blastocyst develops into an adult mouse, every cell its body will have the modification of interest. This is possible because scientists can modify the genome of a mouse in its ES cells and then inject those modified cells into mouse blastocysts. This discovery opened the doors to the creation of “murine genetic models,” which are mice that have had one or several of their genes deleted or otherwise modified to study their function in disease. Martin Evans (Nobel Prize, 2007) and Matt Kauffman were the first to identify, isolate and successfully culture ES cells using mouse blastocysts in 1981. Reprogramming committed adult cells into stem cells: from frog to man Cell types obtained by differentiation of either ES cell (Left) or iPS cells (Right) can then be studied in the dish or used for transplantation into patients. Right: An alternative route to obtain pluripotent stem cells is the generation of induced pluripotent stem cells (iPS cells) from patients. ES cells are pluripotent and can thus give rise to all cell types in our body, including adult stem cells, which range from multipotent to unipotent. Left: The fertilized egg (totipotent) develops into a 300-cell structure, the blastocyst, which contains embryonic stem cells (ES cells) at the inner cell mass (ICM). Still, what ultimately fueled the enormous impact that the stem cell research field has today is undoubtedly the isolation and generation of pluripotent stem cells, which will be the main focus of the remainder of the text.įigure 1: Varying degrees of stem cell potency. Therefore, the foundations of stem cell research lie not with the famous (or infamous) human embryonic stem cells, but with HSCs, which have been used in human therapy (such as bone marrow transplants) for decades. Called satellite cells, these muscle cells are unipotent, as they can give rise to just one cell type, muscle cells. Muscle, for instance, also possesses a population of adult stem cells. ![]() They are one of many examples of adult stem cells, which are tissue-specific stem cells that are essential for organ maintenance and repair in the adult body. HSCs are said to be multipotent, as they can still give rise to multiple cell types, but only to other types of blood cells (see Figure 1, left column). By definition, a stem cell must be capable of both self-renewal (undergoing cell division to make more stem cells) and differentiation into mature cell types. In their pioneering work in mice in the 1960s, they discovered the blood-forming stem cell, the hematopoietic stem cell (HSC). Įven though it is hard to pinpoint exactly when or by whom what we now call “stem cells” were first discovered, the consensus is that the first scientists to rigorously define the key properties of a stem cell were Ernest McCulloch and James Till. The latter originate from the trophoblast. They are able to give rise to all the cells in an embryo proper, but not to extra-embryonic tissues, such as the placenta. The ICM is made of embryonic stem cells (ES cells), which are referred to as pluripotent. The blastocyst is a structure comprising about 300 cells that contains two main regions: the inner cell mass (ICM) and the trophoblast. ![]() Along the way, the zygote develops into the blastocyst, which implants into the mother’s uterus. Because of this amazing developmental potential, the zygote is said to be totipotent. Stem cells come in different flavors of potencyįertilization of an egg cell by a sperm cell results in the generation of a zygote, the single cell that, upon a myriad of divisions, gives rise to our whole body. Here, I’ll lay out the basic concepts of stem cell biology as a background for understanding the stem cell research field, where it is headed, and the enormous promise it offers for regenerative medicine. Surprisingly, though, not everybody understands the basic properties of stem cells, let alone the fact that there is more than one type of cell that falls within the “stem cell” category. Stem cells have been the object of much excitement and controversy amongst both scientists and the general population. ![]()
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