蠕虫肌肉与椎间盘突出
文章来源:未知 文章作者:enread 发布时间:2014-09-16 07:08 字体: [ ]  进入论坛
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Thoughts of the family tree may not be uppermost in the mind of a person suffering from a slipped disc, but those spinal1 discs provide a window into our evolutionary2 past. They are remnants of the first vertebrate skeleton, whose origins now appear to be older than had been assumed. Scientists at the European Molecular3 Biology Laboratory (EMBL) in Heidelberg, Germany, have found that, unexpectedly, this skeleton most likely evolved from a muscle. The study, carried out in collaboration4 with researchers at the Howard Hughes Medical Institute in Janelia Farm, USA, is published today in Science.
 
Humans are part of a group of animals called chordates, whose defining feature is a rod of cartilage that runs lengthwise along the middle of their body, under their spinal chord. This structure, called the notochord, was the first vertebrate skeleton. It is present in human embryos5, and is replaced with the backbone6 as we develop, with the cartilage reduced to those tell-tale discs. Since starfish, sea urchins7 and related animals have no such structure, scientists assumed the notochord had emerged in a relatively8 recent ancestor, after our branch of the evolutionary tree split away from the 'starfish branch'.
 
"People simply haven't been looking beyond our direct relatives, but that means you could be fooled, if the structure appeared earlier and that single group lost it," says Detlev Arendt from EMBL, who led the study. "And in fact, when we looked at a broader range of animals, this is what we found."
 
Antonella Lauri and Thibaut Brunet, both in Arendt's lab, identified the genetic9 signature of the notochord -- the combination of genes10 that have to be turned on for a healthy notochord to form. When they found that the larva of the marine11 worm Platynereis has a group of cells with that same genetic signature, the scientists teamed up with Philipp Keller's group at Janelia Farm to use state-of-the-art microscopy to follow those cells as the larva developed. They found that the cells form a muscle that runs along the animal's midline, precisely12 where the notochord would be if the worm were a chordate. The researchers named this muscle the axochord, as it runs along the animal's axis13. A combination of experimental work and combing through the scientific literature revealed that most of the animal groups that sit between Platynereis and chordates on the evolutionary tree also have a similar, muscle-based structure in the same position.
 
The scientists reason that such a structure probably first emerged in an ancient ancestor, before all these different animal groups branched out on their separate evolutionary paths. Such a scenario14 would also explain why the lancelet amphioxus, a 'primitive15' chordate, has a notochord with both cartilage and muscle. Rather than having acquired the muscle independently, amphioxus could be a living record of the transition from muscle-based midline to cartilaginous notochord.
 
The shift from muscle to cartilage could have come about because a stiffened16 central rod would make swimming more efficient, the scientists postulate17.


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1 spinal KFczS     
adj.针的,尖刺的,尖刺状突起的;adj.脊骨的,脊髓的
参考例句:
  • After three days in Japan,the spinal column becomes extraordinarily flexible.在日本三天,就已经使脊椎骨变得富有弹性了。
  • Your spinal column is made up of 24 movable vertebrae.你的脊柱由24个活动的脊椎骨构成。
2 evolutionary Ctqz7m     
adj.进化的;演化的,演变的;[生]进化论的
参考例句:
  • Life has its own evolutionary process.生命有其自身的进化过程。
  • These are fascinating questions to be resolved by the evolutionary studies of plants.这些十分吸引人的问题将在研究植物进化过程中得以解决。
3 molecular mE9xh     
adj.分子的;克分子的
参考例句:
  • The research will provide direct insight into molecular mechanisms.这项研究将使人能够直接地了解分子的机理。
  • For the pressure to become zero, molecular bombardment must cease.当压强趋近于零时,分子的碰撞就停止了。
4 collaboration bW7yD     
n.合作,协作;勾结
参考例句:
  • The two companies are working in close collaboration each other.这两家公司密切合作。
  • He was shot for collaboration with the enemy.他因通敌而被枪毙了。
5 embryos 0e62a67414ef42288b74539e591aa30a     
n.晶胚;胚,胚胎( embryo的名词复数 )
参考例句:
  • Somatic cells of angiosperms enter a regenerative phase and behave like embryos. 被子植物体细胞进入一个生殖阶段,而且其行为象胚。 来自辞典例句
  • Evolution can explain why human embryos look like gilled fishes. 进化论能够解释为什么人类的胚胎看起来象除去了内脏的鱼一样。 来自辞典例句
6 backbone ty0z9B     
n.脊骨,脊柱,骨干;刚毅,骨气
参考例句:
  • The Chinese people have backbone.中国人民有骨气。
  • The backbone is an articulate structure.脊椎骨是一种关节相连的结构。
7 urchins d5a7ff1b13569cf85a979bfc58c50045     
n.顽童( urchin的名词复数 );淘气鬼;猬;海胆
参考例句:
  • Some dozen barefooted urchins ganged in from the riverside. 几十个赤足的顽童从河边成群结队而来。 来自《简明英汉词典》
  • People said that he had jaundice and urchins nicknamed him "Yellow Fellow." 别人说他是黄胆病,孩子们也就叫他“黄胖”了。 来自汉英文学 - 中国现代小说
8 relatively bkqzS3     
adv.比较...地,相对地
参考例句:
  • The rabbit is a relatively recent introduction in Australia.兔子是相对较新引入澳大利亚的物种。
  • The operation was relatively painless.手术相对来说不痛。
9 genetic PgIxp     
adj.遗传的,遗传学的
参考例句:
  • It's very difficult to treat genetic diseases.遗传性疾病治疗起来很困难。
  • Each daughter cell can receive a full complement of the genetic information.每个子细胞可以收到遗传信息的一个完全补偿物。
10 genes 01914f8eac35d7e14afa065217edd8c0     
n.基因( gene的名词复数 )
参考例句:
  • You have good genes from your parents, so you should live a long time. 你从父母那儿获得优良的基因,所以能够活得很长。 来自《简明英汉词典》
  • Differences will help to reveal the functions of the genes. 它们间的差异将会帮助我们揭开基因多种功能。 来自英汉非文学 - 生命科学 - 生物技术的世纪
11 marine 77Izo     
adj.海的;海生的;航海的;海事的;n.水兵
参考例句:
  • Marine creatures are those which live in the sea. 海洋生物是生存在海里的生物。
  • When the war broke out,he volunteered for the Marine Corps.战争爆发时,他自愿参加了海军陆战队。
12 precisely zlWzUb     
adv.恰好,正好,精确地,细致地
参考例句:
  • It's precisely that sort of slick sales-talk that I mistrust.我不相信的正是那种油腔滑调的推销宣传。
  • The man adjusted very precisely.那个人调得很准。
13 axis sdXyz     
n.轴,轴线,中心线;坐标轴,基准线
参考例句:
  • The earth's axis is the line between the North and South Poles.地轴是南北极之间的线。
  • The axis of a circle is its diameter.圆的轴线是其直径。
14 scenario lZoxm     
n.剧本,脚本;概要
参考例句:
  • But the birth scenario is not completely accurate.然而分娩脚本并非完全准确的。
  • This is a totally different scenario.这是完全不同的剧本。
15 primitive vSwz0     
adj.原始的;简单的;n.原(始)人,原始事物
参考例句:
  • It is a primitive instinct to flee a place of danger.逃离危险的地方是一种原始本能。
  • His book describes the march of the civilization of a primitive society.他的著作描述了一个原始社会的开化过程。
16 stiffened de9de455736b69d3f33bb134bba74f63     
加强的
参考例句:
  • He leaned towards her and she stiffened at this invasion of her personal space. 他向她俯过身去,这种侵犯她个人空间的举动让她绷紧了身子。
  • She stiffened with fear. 她吓呆了。
17 postulate oiwy2     
n.假定,基本条件;vt.要求,假定
参考例句:
  • Let's postulate that she is a cook.我们假定她是一位厨师。
  • Freud postulated that we all have a death instinct as well as a life instinct.弗洛伊德曾假定我们所有人都有生存本能和死亡本能。
TAG标签: muscle disc spinal
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