Gene expression during embryonic and adult stem cell differentiation.
Gene expression during embryonic and adult stem cell differentiation.
复制标题
胚胎和成体干细胞分化过程中的基因表达。
DOI：
10.1089/scd.2005.14.349
复制
发表时间：
2005
影响因子：
4
通讯作者：
D. English
中科院分区：
文献类型：
--
作者：
D. English
IN RECENT ISSUES, we have called for a reassessment of the defining characteristics of the minimal characteristics that a cell must possess to be considered a stem cell, and have found no consensus. Specifically, we asked if a stem cell must possess the ability to self-replicate while it differentiates into a more mature cell. The opinions we solicited were vehement.“Of course they must self-replicate,” shouted many hematologists.“Otherwise how can they be stem cells?” Others were not so sure. For them a stem cell merely had to contribute to an early and essential process in development. Once done, the cell only needs to self-replicate if this process must continue. The results of our survey, collated by associate editor Graham Parker, were received with wide interest, enthusiasm, and animated feedback. Indeed, further discussion and essays are planned to develop this concept, as it is essential that we define what a stem cell is before we define how it does what it does. In the absence of this information, we can never know if the pathways we implicate in stem cell-initiated development hold physiological relevance. And the result cannot be reached by consensus; it must be reached by experimentation, reason, and logical interpretation of the results. But in these dynamic days of stem cell research, another, perhaps more fundamental, point has now surfaced; and it is a point that needs to be directly and immediately addressed. In recent weeks, several highly respected individuals have openly questioned the concept of “transdifferentiation,” a function that we have assumed provides the basis of stem cell differentiation. Strictly defined, transdifferentiation is the genesis of one type of differentiated somatic cell from another cell type which has already been committed to a different fate, following a change in environment or circumstances. In essence, transdifferentiation implies the induced formation of one type of cell from another. Viewed more liberally, we have come to think that transdifferentiation, also known as “plasticity,” provides the essence of the ability of multipotential stem cells to differentiate into cells of any and all germal layers; to provide from a single progenitor cells of diverse function, morphology, and antigen expression; cells which participate in development in diverse ways. We have considered transdifferentiation to be a fundamental aspect of stem cells, particularly adult mesenchymal stem cells, and a property that is essential for stem cell function in development.But the concept of transdifferentiation is now besieged by individuals who find no evidence that this process occurs in vivo at loci where stem cells home to promote wound healing and protect tissues from further damage as they generate new tissue and structures. Transdifferentiation is considered to be a key element in neoplastic transformation and fundamental to embryonic development by primitive stem cells. Certainly, studies in vitro add credence that transdifferentiation of cells identified as stem cells is readily observed when these cells are exposed to various differentiating agents: neural factors induce neural antigen expression, while osteogenic factors induce these cells to express antigens specific for bone. However, recent reports question the in vivo relevance of these findings. These reports have questioned the identity of the cells’ progeny and the ability of putative stem cells to generate new tissues of diverse cellular composition. In this respect, early reports held that the wellstudied endothelial progenitor cells were, in fact, CD-14 positive monocytes that integrated into the damaged and repairing vasculature for a short time, while tissue regeneration was effected by …
