美国和澳大利亚科学家近日研究发现，果蝇成体干细胞内的一种分子信使就像城堡的岗哨一样，当感觉到癌症入侵风险的时候，会发出警报。随后，细胞分裂被中止，防止了细胞分裂失控及肿瘤的形成。相关论文10月15日在线发表于《自然》（Nature）杂志上。
美国密歇根大学生命科学研究所的Yukiko Yamashita和同事以果蝇作为实验对象，研究发现，细胞分裂部分由中心体（centrosome）控制，它提供了有助引导染色体分散到子细胞中的框架。正常情况下，中心体与临近的信使细胞相垂直，而当中心体出现不正确定位，就会破坏有丝分裂机器，使其朝向干细胞过度增殖和癌症方向进行。
检查站机制能感觉到中心体的偏离，随后拉响警报，终止细胞分裂，阻止癌症入侵。Yamashita说：“我们的研究显示，为了阻止会导致癌症的异常细胞增殖，干细胞发展出了这种自我检查系统，我们称作‘检查站’。如果一个细胞看起来要以错误的方式分裂，检查站就会感觉到并发出信号：‘别分裂！别分裂！’。”
但是存在一个平衡问题：如果检查站机制将细胞分裂降低到极低程度，那么就会缺乏新细胞，从而加速组织的衰老。她说：“衰老是过少的分裂，而癌症是过多的分裂，人们长期以来推测一定有程序控制着二者的平衡。我们可能发现了维持会导致癌症的过度增殖和衰老之间精致平衡的机制。”
如果人类具有相似的检查站机制并且将来能被研究人员利用的话，我们就能调整细胞分裂的速度，来控制肿瘤形成以及组织衰老。不过Yamashita强调，现在尚无类似的哺乳动物研究，谈人类应用还为时过早。
Yamashita说：“这是一把双刃剑，两面均可伤人。一条路径导致癌症，另一条则会导致衰老，而我们尚未找到能避免衰老且不会罹患癌症的方法。”（生物谷Bioon.com）
生物谷推荐原始出处：
Nature，doi:10.1038/nature07386，Jun Cheng，Yukiko M. Yamashita
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
Department of Biomedical Engineering, Center for Ultrafast Optical Science
Life Sciences Institute, Center for Stem Cell Biology,
Department of Cell and Developmental Biology, University of Michigan, Ann Arbor, Michigan 48109, USA
Departments of Developmental Biology and Genetics, Stanford University, School of Medicine, Stanford, California 94305, USA
These authors contributed equally to this work.
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.
