Chai Phing Chian, Chia William, Cai Yu
Temasek Life Sciences Laboratory, National University of Singapore, Singapore, Singapore.
Wiley Interdiscip Rev Dev Biol. 2012 Mar-Apr;1(2):307-14. doi: 10.1002/wdev.27. Epub 2011 Dec 27.
Stem cells, which can self-renew and give rise to differentiated daughters, are responsible for the generation of diverse cell types during development and the maintenance of tissue/organ homeostasis in adulthood. Thus, the precise regulation of stem-cell self-renewal and proliferative potential is a key aspect of development. The stem-cell niche confers such control by concentrating localized factors including signaling molecules which favor stem-cell self-renew and regulate stem-cell proliferation in line with developmental programs. In contrast, Drosophila neuroblasts (NBs), often referred to as neural stem cells/progenitors, can undergo asymmetric cell division to self-renew and produce differentiated daughters even in isolation (or in culture). Furthermore, these isolated NBs can also progress through an intrinsically regulated temporal series (of transcription factor expression) to generate diverse cell types in vitro. These data argue that NBs may depend only to a limited extent, if at all, on local environment (a niche) for their maintenance. On the other hand, there is increasing evidence which indicate that the interaction between NBs and their surrounding glia is critical for the control of NB proliferative potential and these glia, in conjunction with systemic regulation, perform the niche function to regulate NB behavior. Thus, these observations emphasize the importance of coordinated local microenvironment (niche activity) and systemic environment (global activity) on the regulation of NB behavior in vivo, and suggest NBs may conform to an alternative stem-cell/progenitor maintenance model.
干细胞能够自我更新并产生分化的子代细胞，在发育过程中负责产生多种细胞类型，并在成年期维持组织/器官的稳态。因此，精确调控干细胞的自我更新和增殖潜能是发育的一个关键方面。干细胞微环境通过聚集局部因子（包括信号分子）来实现这种控制，这些因子有利于干细胞自我更新，并根据发育程序调节干细胞增殖。相比之下，果蝇神经母细胞（NBs），常被称为神经干细胞/祖细胞，即使在孤立状态（或培养中）也能进行不对称细胞分裂以自我更新并产生分化的子代细胞。此外，这些孤立的神经母细胞还可以通过内在调节的时间序列（转录因子表达）在体外产生多种细胞类型。这些数据表明，神经母细胞维持自身状态可能仅在有限程度上依赖于局部环境（微环境），甚至可能完全不依赖。另一方面，越来越多的证据表明，神经母细胞与其周围神经胶质细胞之间的相互作用对于控制神经母细胞的增殖潜能至关重要，并且这些神经胶质细胞与系统调节共同发挥微环境功能来调节神经母细胞的行为。因此，这些观察结果强调了协调局部微环境（微环境活性）和系统环境（整体活性）对体内神经母细胞行为调控的重要性，并表明神经母细胞可能符合另一种干细胞/祖细胞维持模型。
