血液、表皮和精液中的成年干細胞,，通過非對稱分裂維持高度分異的短壽命細胞群,，在每次分裂時產(chǎn)生一個可以自我更新的干細胞和一個正在分異的細胞。打破更新與分異之間的平衡,，會導(dǎo)致過度增殖（及形成腫瘤）或干細胞耗盡（及組織退化）,。
Cheng等人利用果蠅雄性精細胞系作為模型，研究了組織衰老對非對稱干細胞分裂的影響,。正常情況下,，生殖細胞中心體的取向精確地位于它們的小環(huán)境內(nèi)，非對稱干細胞分裂肯定可以進行,。實驗表明,，干細胞取向隨年齡的變化會阻止或延遲細胞分裂,，造成精子生成量的減少。（生物谷Bioon.com）
生物谷推薦原始出處：
Centrosome misorientation reduces stem cell division during ageing
Jun Cheng1,5, Nezaket Türkel2,5,6, Nahid Hemati2,5, Margaret T. Fuller4, Alan J. Hunt1 & Yukiko M. Yamashita2,3
1 Department of Biomedical Engineering, Center for Ultrafast Optical Science
2 Life Sciences Institute, Center for Stem Cell Biology,
3 Department of Cell and Developmental Biology, University of Michigan, Ann Arbor, Michigan 48109, USA
4 Departments of Developmental Biology and Genetics, Stanford University, School of Medicine, Stanford, California 94305, USA
5 These authors contributed equally to this work.
6 Present address: Peter MacCallum Cancer Centre, Anatomy and Cell Biology Department, University of Melbourne, Melbourne, Victoria 3002, Australia.
Asymmetric division of adult stem cells generates one self-renewing stem cell and one differentiating cell, thereby maintaining tissue homeostasis. A decline in stem cell function has been proposed to contribute to tissue ageing, although the underlying mechanism is poorly understood. Here we show that changes in the stem cell orientation with respect to the niche during ageing contribute to the decline in spermatogenesis in the male germ line of Drosophila. Throughout the cell cycle, centrosomes in germline stem cells (GSCs) are oriented within their niche and this ensures asymmetric division. We found that GSCs containing misoriented centrosomes accumulate with age and that these GSCs are arrested or delayed in the cell cycle. The cell cycle arrest is transient, and GSCs appear to re-enter the cell cycle on correction of centrosome orientation. On the basis of these findings, we propose that cell cycle arrest associated with centrosome misorientation functions as a mechanism to ensure asymmetric stem cell division, and that the inability of stem cells to maintain correct orientation during ageing contributes to the decline in spermatogenesis. We also show that some of the misoriented GSCs probably originate from dedifferentiation of spermatogonia.
