A morphological study of nonrandom senescence in a colonial urochordate
A morphological study of nonrandom senescence in a colonial urochordate
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DOI：
10.2307/1542692
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发表时间：
2000-06-01
影响因子：
1.6
通讯作者：
Weissman, IL
中科院分区：
文献类型：
--
作者：
Lauzon, RJ;Rinkevich, B;Weissman, IL
Schlosseri是一种克隆模块海鞘，其中个体（zoids）具有有限的寿命，这与每周的芽生过程密切相关，称为囊胚发生。每一个胚发生周期都以一个被称为接管的同步退化阶段结束，在此期间，菌落中的所有动物都死亡，主要是通过细胞凋亡，并被新一代无性衍生的动物所取代。我们以前已经证明，除了这个周期性的死亡阶段，整个殖民地经历衰老，在此期间，所有无性繁殖的个体在一个殖民地，芽和zoids，一致死亡。此外，当一个特定的亲本群体（基因组）实验分离成许多克隆复制（分株），分株经常同时进行衰老，表明死亡率可以体现在非随机的方式。在这里，我们记录了一个形态学的肖像，从蒙特雷湾，加州，表现出非随机死亡率在实验室维持的殖民地衰老。在大约一周的时间内，根据殖民地内一系列特征性变化进行非随机衰老。这些变化包括全身性收缩和血管充血，伴随色素细胞在动物体壁（外套膜）、血管和壶腹中的大量积累;个体动物逐渐萎缩;群体结构丧失，最终死亡。在超微结构水平，个别细胞表现出典型的缺血性细胞死亡的变化，最终在坏死细胞溶解，而不是凋亡。总的来说，这些观察结果表明，衰老是伴随着独特的形态学变化，发生系统性的，这是不同于那些发生在接管。我们讨论了我们的研究结果与目前的实验模型老化和体液因素的可能作用，使衰老的发病。
Botryllus schlosseri is a clonally modular ascidian, in which individuals (zooids) have a finite lifespan that is intimately associated with a weekly budding process called blastogenesis. Every blastogenic cycle concludes with a synchronized phase of regression called takeover, during which all zooids in a colony die, primarily by apoptosis, and are replaced by a new generation of asexually derived zooids. We have previously documented that, in addition to this cyclical death phase, entire colonies undergo senescence during which all asexually derived individuals in a colony, buds and zooids, die in concert. In addition, when a specific parent colony (genet) is experimentally separated into a number of clonal replicates (ramets), ramets frequently undergo senescence simultaneously, indicating that mortality can manifest itself in nonrandom fashion. Here, we document a morphological portrait of senescence in laboratory-maintained colonies from Monterey Bay, California, that exhibit nonrandom mortality. Nonrandom senescence proceeded according to a series of characteristic changes within the colony over a period of about one week. These changes included systemic constriction and congestion of the vasculature accompanied by massive accumulation of pigment cells in the zooid body wall (mantle), blood vessels, and ampullae; gradual shrinkage of individual zooids; loss of colonial architecture, and ultimately death. At the ultrastructural level, individual cells exhibited changes typical of ischemic cell death, culminating in necrotic cell lysis rather than apoptosis. Collectively, these observations indicate that senescence is accompanied by unique morphological changes that occur systemically, and which are distinct from those occurring during takeover. We discuss our findings in relation to current experimental models of aging and the possible role of a humoral factor in bringing about the onset of senescence.