Shanghai Hengyuan tells you the classification of stem cells. Stem cells can be divided into two types, which are embryonic stem cells and tissue stem cells. They have both the common characteristics of stem cells and their different biological characteristics. 1. Embryonic stem cells Embryonic stem cells refer to undifferentiated cells derived from early embryonic tissues and having high self-renewal and multi-directional differentiation potential. Embryonic stem cells can differentiate into almost all types of cells in the three germ layers, so they are also totipotent stem cells. Embryonic stem cells include three types: embryonic stem cells (ES cells), embryonic germ cells (EG cells), and embryonic carcinoma cells (EC cells). Inner cell masses (ICMs) from preimplantation blastocysts can be isolated and cultured in vitro to establish a totipotent stem cell line-the ES cell line; primordial germ cells (PGC) from the embryonic reproductive crest after proper isolation and culture It can also produce pluripotent stem cells-EG cells; fetal cancer cells from malignant teratoma have also been found to contain stem cells. ES cells and EG cells have normal karyotypes and chromosome numbers, and their culture conditions in vitro have been basically mature, and various induction and genetic operations can be performed. In addition to the basic characteristics of stem cells, embryonic stem cells have their own unique features. First of all, embryonic stem cells have a strong self-renewal ability, which is permanent. As embryonic stem cells are cultured in vitro, most of them can maintain symmetrical division and produce the same offspring stem cells as the parent. Therefore, embryonic stem cells based on this renewal method can theoretically maintain the ability of unlimited proliferation. Second, embryonic stem cells have the broadest differentiation potential and can differentiate into all cells derived from three germ layers. In the presence of feeder cells or the addition of differentiation inhibitory factors, embryonic stem cells can maintain stem cell characteristics for a long time. Embryonic stem cells can grow in suspension when inoculated on a plate without feeder layers, forming embryoid bodies similar to early embryos before implantation. With continued cultivation, the embryoid body will continue to grow, differentiate into an endoderm-like structure, and spontaneously differentiate into a mixture of neurons, hematopoietic systems, and mesodermal-derived cells such as bone, cartilage, and fat. Inoculation of embryonic stem cells under the skin of nude mice can produce teratoma tumors including stem cells, interstitial cells and hair, epithelium, neural tube and Other structures due to the disordered differentiation of cells. Because embryonic stem cells have unlimited proliferation and comprehensive differentiation capabilities, they have extremely broad prospects in the application of modern biotechnology such as cell and tissue engineering. However, embryonic stem cell research is also facing a very confusing medical ethics problem, and has caused fierce ethical and political disputes, so its real application still has a long way to go. 2. Adult stem cells Many adult tissues and organs, such as the epidermis and hematopoietic system, have the ability to repair and regenerate, and undifferentiated cells play a key role in them. Such undifferentiated cells present in differentiated tissues are adult stem cells. Because they exist in various tissues and organs, adult stem cells are also called tissue stem cells. Under certain conditions, tissue stem cells can produce asymmetric division, resulting in a progeny stem cell and a progeny cell. The latter has only limited self-renewal capacity and can differentiate according to a certain procedure to form new functional cells, thereby keeping tissues and organs in a dynamic balance of growth and decline. Hematopoietic stem cells are the longest-studied tissue stem cells. As early as 1968, people conducted more in-depth research on them, and they have been widely used in clinical practice. Recent studies have shown that there are still stem cells in neural tissues that were previously thought to be non-renewable, indicating that tissue stem cells are widespread. At present, there have been a large number of reports confirming that there are corresponding tissue stem cells in almost all mature tissues, such as hematopoietic stem cells, bone marrow stromal stem cells, adipose stem cells, neural stem cells, epidermal stem cells, corneal stem cells, visceral stem cells, intestinal stem cells, etc. . Because tissue stem cells have no ethical issues and have a good multi-directional differentiation potential, they have become a research hotspot in recent years. In later chapters, we will explain in detail the characteristics of adult stem cells. 3. Pluripotent adult stem cells Only stem cells from early embryos have a totipotent differentiation ability, which is the conclusion made by most stem cell researchers. However, the concept of "universal" adult stem cells has recently been proposed. Verfaillie et al. Discovered a special class of cells when studying stem cells in adult bone marrow, and named them multipotent adult progenitor cells (MAPC). Verfaillie and others passed a series of experiments to confirm the presence of MAPC cells in human and rat bone marrow tissues. MAPC cells have similar characteristics to ES cells, such as in vitro expansion of more than 100 cell doublings (population doublings); a single MAPC cell can differentiate into osteoblasts, cartilage, muscle, fat, fibroblasts and endothelial cells, Neuroectodermal cells, liver cells, etc. Injecting MAPC cells into blastocysts still produces all somatic cell types. MPAC cells have many characteristics of ES cells, but they are not the same. For example, injection of MPAC into human adult will not form teratoma. Although the basic characteristics of MPAC cells have not been fully studied, and there is even controversy about their existence, but they have some advantages of embryonic stem cells, but there are no complicated ethical issues, so it may be a new direction of stem cell development. This is Shanghai Hengyuan Biological Technology Co., Ltd. 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January 14, 2021