The historical roots of the stem cell concept are traced with respect to its usage in embryology and in hematology. The modern consensus definition of stem cells, comprising both pluripotent stem cells in culture and tissue‐specific stem cells in vivo, is explained and explored. Methods for identifying stem cells are discussed with respect to cell surface markers, telomerase, label retention and transplantability, and properties of the stem cell niche are explored. The CreER method for identifying stem cells in vivo is explained, as is evidence in favor of a stochastic rather than an obligate asymmetric form of cell division. In conclusion, it is found that stem cells do not possess any unique and specific molecular markers; and stem cell behavior depends on the environment of the cell as well as the stem cell's intrinsic qualities. Furthermore, the stochastic mode of division implies that stem cell behavior is a property of a cell population not of an individual cell. In this sense, stem cells do not exist in isolation but only as a part of multicellular system.

中文翻译：

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什么是干细胞？

干细胞概念的历史根源可追溯到其在胚胎学和血液学中的用途。对干细胞的现代共识定义进行了解释和探索，包括培养中的多能干细胞和体内组织特异性干细胞。关于细胞表面标志物，端粒酶，标签保留和可移植性的鉴定干细胞的方法进行了讨论，并探讨了干细胞小生境的特性。解释了在体内识别干细胞的CreER方法，以及支持随机而不是专心不对称形式的细胞分裂的证据。总之，发现干细胞不具有任何独特和特异性的分子标记。干细胞的行为取决于细胞的环境以及干细胞的内在品质。此外，随机的分裂方式意味着干细胞行为是细胞群体的属性，而不是单个细胞的属性。从这个意义上说，干细胞不是孤立存在的，而只是多细胞系统的一部分。