来自伦敦大学学院(UCL)的胚胎学家最近解决了一个困扰科学家一个多世纪的谜题。他们发现了在胚胎发育最初阶段帮助较高级进化生物—包括人类-从低级生物例如鱼类中分离出来的关键机制。以上结果发表在10月10日在线版Nature上。
在发育早期,很多未分化细胞构成的胚胎首先需要确定如何排列,以最终形成完全发育的身体。这一过程称为“原肠胚形成”。
在这一阶段,细胞分化为3层,第一层是“外胚层”,它最终会形成中胚层和内胚层。在高等脊椎动物(例如哺乳动物和鸟类)中,中胚和内胚层在胚胎中心的轴部产生。但是在低等动物(例如两栖类和鱼类)中,这两个胚层沿着胚胎边缘产生。
利用鸡卵和能反应细胞三维移动的最新成像设备,科学家证明了高等脊椎动物和低等动物之间原肠胚形成的差异。研究小组发现,高等脊椎动物在胚胎中间形成轴的原因在于进化中,它们需要新的“细胞插入”机制。小组同时发现了胚胎用来控制这些细胞移动的分子。
关于高等脊椎动物和低等脊椎动物胚胎发育的区别,科学家已经思考了一个多世纪。这能帮助解释胚胎简单的细胞结构如何形成各种高度复杂的物种身体。研究负责人Claudio Stern教授表示:“这是很重要的发现,高等和低等物种的胚胎发育之间存在明显的区别。这意味着高等脊椎动物是在动物进化的较晚期发展出的这种机制。”在人类中,以上过程发生于胚胎发育的第3周。(教育部科技发展中心)
原文链接:http://www.physorg.com/news111241765.html
原始出处:
Nature advance online publication 10 October 2007 | doi:10.1038/nature06211; Received 4 April 2007; Accepted 31 August 2007; Published online 10 October 2007
The amniote primitive streak is defined by epithelial cell intercalation before gastrulation
Octavian Voiculescu1, Federica Bertocchini1, Lewis Wolpert1, Ray E. Keller2 & Claudio D. Stern1
Department of Anatomy & Developmental Biology, University College London, Gower Street, London WC1E 6BT, UK
Department of Biology, Gilmer Hall, University of Virginia, Charlottesville, Virginia 22903, USA
Correspondence to: Octavian Voiculescu1Claudio D. Stern1 Correspondence and requests for materials should be addressed to O.V. (Email: o.voiculescu@ucl.ac.uk) or C.D.S. (Email: c.stern@ucl.ac.uk).
During gastrulation, a single epithelial cell layer, the ectoderm, generates two others: the mesoderm and the endoderm. In amniotes (birds and mammals), mesendoderm formation occurs through an axial midline structure, the primitive streak1, the formation of which is preceded by massive 'polonaise' movements2, 3 of ectoderm cells. The mechanisms controlling these processes are unknown. Here, using multi-photon time-lapse microscopy of chick (Gallus gallus) embryos, we reveal a medio-lateral cell intercalation confined to the ectodermal subdomain where the streak will later form. This intercalation event differs from the convergent extension movements of the mesoderm described in fish and amphibians (anamniotes)4, 5, 6, 7, 8: it occurs before gastrulation and within a tight columnar epithelium. Fibroblast growth factor from the extraembryonic endoderm (hypoblast, a cell layer unique to amniotes) directs the expression of Wnt planar-cell-polarity pathway components to the intercalation domain. Disruption of this Wnt pathway causes the mesendoderm to form peripherally, as in anamniotes1, 9. We propose that the amniote primitive streak evolved from the ancestral blastopore by acquisition of an additional medio-lateral intercalation event, preceding gastrulation and acting independently of mesendoderm formation to position the primitive streak at the midline.