Tran J, Brenner T J, DiNardo S
Department of Cell & Developmental Biology, University of Pennsylvania Medical Center, Philadelphia 19104-6058, USA.
Nature. 2000 Oct 12;407(6805):754-7. doi: 10.1038/35037613.
Stem cells divide both to produce new stem cells and to generate daughter cells that can differentiate. The underlying mechanisms are not well understood, but conceptually are of two kinds. Intrinsic mechanisms may control the unequal partitioning of determinants leading to asymmetric cell divisions that yield one stem cell and one differentiated daughter cell. Alternatively, extrinsic mechanisms, involving stromal cell signals, could cause daughter cells that remain in their proper niche to stay stem cells, whereas daughter cells that leave this niche differentiate. Here we use Drosophila spermatogenesis as a model stem cell system to show that there are excess stem cells and gonialblasts in testes that are deficient for Raf activity. In addition, the germline stem cell population remains active for a longer fraction of lifespan than in wild type. Finally, raf is required in somatic cells that surround germ cells. We conclude that a cell-extrinsic mechanism regulates germline stem cell behaviour.
干细胞既能分裂产生新的干细胞，也能生成可分化的子细胞。其潜在机制尚未完全明确，但从概念上讲有两种类型。内在机制可能控制决定因素的不均等分配，导致不对称细胞分裂，产生一个干细胞和一个分化的子细胞。或者，涉及基质细胞信号的外在机制可能导致留在其合适微环境中的子细胞保持为干细胞，而离开该微环境的子细胞则发生分化。在这里，我们以果蝇精子发生作为模型干细胞系统，来表明在缺乏Raf活性的睾丸中存在过量的干细胞和精原细胞。此外，生殖系干细胞群体在寿命中保持活跃的时间比例比野生型更长。最后，在包围生殖细胞的体细胞中需要raf。我们得出结论，一种细胞外机制调节生殖系干细胞的行为。
