來自倫敦大學(xué)學(xué)院（UCL）的胚胎學(xué)家最近解決了一個困擾科學(xué)家一個多世紀(jì)的謎題。他們發(fā)現(xiàn)了在胚胎發(fā)育最初階段幫助較高級進(jìn)化生物—包括人類－從低級生物例如魚類中分離出來的關(guān)鍵機(jī)制,。以上結(jié)果發(fā)表在10月10日在線版Nature上。
在發(fā)育早期,，很多未分化細(xì)胞構(gòu)成的胚胎首先需要確定如何排列,，以最終形成完全發(fā)育的身體。這一過程稱為“原腸胚形成”,。
在這一階段，細(xì)胞分化為3層,，第一層是“外胚層”,，它最終會形成中胚層和內(nèi)胚層。在高等脊椎動物（例如哺乳動物和鳥類）中,，中胚和內(nèi)胚層在胚胎中心的軸部產(chǎn)生,。但是在低等動物（例如兩棲類和魚類）中，這兩個胚層沿著胚胎邊緣產(chǎn)生,。
利用雞卵和能反應(yīng)細(xì)胞三維移動的最新成像設(shè)備,，科學(xué)家證明了高等脊椎動物和低等動物之間原腸胚形成的差異。研究小組發(fā)現(xiàn),，高等脊椎動物在胚胎中間形成軸的原因在于進(jìn)化中,，它們需要新的“細(xì)胞插入”機(jī)制。小組同時發(fā)現(xiàn)了胚胎用來控制這些細(xì)胞移動的分子,。
關(guān)于高等脊椎動物和低等脊椎動物胚胎發(fā)育的區(qū)別,，科學(xué)家已經(jīng)思考了一個多世紀(jì)。這能幫助解釋胚胎簡單的細(xì)胞結(jié)構(gòu)如何形成各種高度復(fù)雜的物種身體,。研究負(fù)責(zé)人Claudio Stern教授表示：“這是很重要的發(fā)現(xiàn),，高等和低等物種的胚胎發(fā)育之間存在明顯的區(qū)別。這意味著高等脊椎動物是在動物進(jìn)化的較晚期發(fā)展出的這種機(jī)制,。”在人類中,，以上過程發(fā)生于胚胎發(fā)育的第3周。(教育部科技發(fā)展中心)
原文鏈接：http://www.physorg.com/news111241765.html
原始出處：
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: [email protected]) or C.D.S. (Email: [email protected]).
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.
