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Nature 5月12日内容摘要
巨型水母（Cubozoans）每个有24只四种类型的眼睛，但却没有用于信息处理的中央大脑。对这些眼睛所做的一项研究显示，它们的光学系统同脊椎动物的光学系统一样复杂。尽管如此，其视网膜却在焦点之外，清楚的图像不是用来看清东西的，而是作为处理视觉信息的一种方式。“模糊的”视图也许对避开静止的大目标、同时又不必关注小的漂浮目标和浮游生物非常有利。在动物视觉系统的早期演化中有一个缺少的环节，在这个环节中眼睛很可能只执行单一的任务，即看东西。关于巨型水母眼睛研究的新发现也为了解这个缺少的环节提供了一个线索。本期封面所示为本研究中所用的Chiropsalmus sp.的两只透镜眼睛和两对色素坑眼睛，它们比Tripedalia cystophora的眼睛大，但却与其相似。摄影：Dan-E. Nilsson。
Nature 435, 201-205 (12 May 2005) | doi: 10.1038/nature03484
Advanced optics in a jellyfish eye
Cubozoans, or box jellyfish, differ from all other cnidarians by an active fish-like behaviour and an elaborate sensory apparatus1, 2. Each of the four sides of the animal carries a conspicuous sensory club (the rhopalium), which has evolved into a bizarre cluster of different eyes3. Two of the eyes on each rhopalium have long been known to resemble eyes of higher animals, but the function and performance of these eyes have remained unknown4. Here we show that box-jellyfish lenses contain a finely tuned refractive index gradient producing nearly aberration-free imaging. This demonstrates that even simple animals have been able to evolve the sophisticated visual optics previously known only from a few advanced bilaterian phyla. However, the position of the retina does not coincide with the sharp image, leading to very wide and complex receptive fields in individual photoreceptors. We argue that this may be useful in eyes serving a single visual task. The findings indicate that tailoring of complex receptive fields might have been one of the original driving forces in the evolution of animal lenses.
能自我复制的机器人
自我复制是活生物的一个特性，但却在很大程度上被工程师和材料学家所忽略，他们对一次性的自组装更感兴趣。但自我复制也有非常有用的时候，在本期Nature上，研究人员通过能够进行物理自我复制的简单机器的研制，向我们展示了非生命世界在这个方向上能走多远。这些简单的机器是模块化的机器人，每个10厘米长的模块都有电磁铁，能够选择性地削弱和增强连接，从而决定体系结构在什么地方断开和接合。一个由三个模块构成的机器人能在仅仅一分钟多的时间内完成复制（关于这种本领的影片，请看补充信息）。与生物体系相比虽然简单，但这些机器人说明，自我复制并不是生物特有的。这种设计概念对于危险环境中的自持系统的设计可能是有用的，如在空间探索中所遇到的环境条件，在这些环境条件下采用传统维护方法是不现实的。
Nature 435, 163-164 (12 May 2005) | doi: 10.1038/435163a
Robotics: Self-reproducing machines
Self-reproduction is central to biological life for long-term sustainability and evolutionary adaptation. Although these traits would also be desirable in many engineered systems, the principles of self-reproduction have not been exploited in machine design1. Here we create simple machines that act as autonomous modular robots and are capable of physical self-reproduction using a set of cubes.
决定身体组织对称性的因素
虽然从外面看是对称的，但脊椎动物和其他动物的身体结构从里面看却远不是对称的。当人类心脏和肺在胚胎中形成的时候，它们是朝向体腔左侧和右侧的。为了确定形成这种不对称性的遗传规律和信号机制，科学家进行了很多研究，但却存在这样一个困难：一些组织，主要是肌肉和骨骼组织，必须忽略或抵制让其对称的指令才能成为不对称的结构。本期Nature上有三篇论文和由Eran Hornstein 和Clifford J. Taboin撰写的一篇News and Views文章，探讨了形成对称组织的胚胎元素“体节”（somites）是怎样实现不对称性的这一有趣的问题。
Nature 435, 165-171 (12 May 2005) | doi: 10.1038/nature03512
Retinoic acid signalling links left−right asymmetric patterning and bilaterally symmetric somitogenesis in the zebrafish embryo
During embryogenesis, cells are spatially patterned as a result of highly coordinated and stereotyped morphogenetic events. In the vertebrate embryo, information on laterality is conveyed to the node, and subsequently to the lateral plate mesoderm, by a complex cascade of epigenetic and genetic events, eventually leading to a left−right asymmetric body plan. At the same time, the paraxial mesoderm is patterned along the anterior−posterior axis in metameric units, or somites, in a bilaterally symmetric fashion. Here we characterize a cascade of laterality information in the zebrafish embryo and show that blocking the early steps of this cascade (before it reaches the lateral plate mesoderm) results in random left−right asymmetric somitogenesis. We also uncover a mechanism mediated by retinoic acid signalling that is crucial in buffering the influence of the flow of laterality information on the left−right progression of somite formation, and thus in ensuring bilaterally symmetric somitogenesis.
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作者:admin@医学,生命科学 2011-04-18 17:14
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