Germ layer differentiation during early hindgut and cloaca formation in rabbit and pig embryos
Germ layer differentiation during early hindgut and cloaca formation in rabbit and pig embryos
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DOI：
10.1111/j.1469-7580.2010.01303.x
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发表时间：
2010-09
影响因子：
2.4
通讯作者：
Romia Hassoun;P. Schwartz;D. Rath;C. Viebahn;J. Männer
中科院分区：
文献类型：
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作者：
Romia Hassoun;P. Schwartz;D. Rath;C. Viebahn;J. Männer
相对于最近的进展，了解内胚层分化的分子要求，胚层形态的动态和地形分布的分子因素参与内胚层形成在胚胎盘的尾极仍然定义不清。为了发现哺乳动物胚层发育的共同原则，使用相关的光学和电子显微镜，将处于原肠胚形成晚期和神经胚形成早期阶段的猪和兔胚胎作为具有类似人的胚胎盘形态的物种进行分析。细胞间的紧密接触，但没有发现内胚层形成的直接结构证据，如后原条中胚层和新出现的后内胚层之间的间充质-上皮转化。然而，泄殖腔膜的形成出现了一个与后胚层分化密切相关的两步过程：（i）连续的中胚层和大量电子致密絮状细胞外基质标记泄殖腔膜形成的预期区域;和（ii）中胚层细胞和包括基底膜的所有细胞外基质局部丧失，并在内胚层和外胚层之间建立紧密的细胞间接触。后一个过程首先涉及单个细胞，然后逐渐扩散形成纵向定向的缝状泄殖腔膜。在猪中从原肠胚形成到早期体节阶段发现了这些逐渐变化，而在兔中从早期体节到中期体节阶段发现了这些逐渐变化;在这两个物种中，泄殖腔膜形成在次级神经胚形成之前完成。结果强调了后肠发育过程中内胚层形成的结构要求，并提出了常见泌尿生殖系统和肛门直肠畸形发病机制的新机制。
Relative to recent advances in understanding molecular requirements for endoderm differentiation, the dynamics of germ layer morphology and the topographical distribution of molecular factors involved in endoderm formation at the caudal pole of the embryonic disc are still poorly defined. To discover common principles of mammalian germ layer development, pig and rabbit embryos at late gastrulation and early neurulation stages were analysed as species with a human‐like embryonic disc morphology, using correlative light and electron microscopy. Close intercellular contact but no direct structural evidence of endoderm formation such as mesenchymal–epithelial transition between posterior primitive streak mesoderm and the emerging posterior endoderm were found. However, a two‐step process closely related to posterior germ layer differentiation emerged for the formation of the cloacal membrane: (i) a continuous mesoderm layer and numerous patches of electron‐dense flocculent extracellular matrix mark the prospective region of cloacal membrane formation; and (ii) mesoderm cells and all extracellular matrix including the basement membrane are lost locally and close intercellular contact between the endoderm and ectoderm is established. The latter process involves single cells at first and then gradually spreads to form a longitudinally oriented seam‐like cloacal membrane. These gradual changes were found from gastrulation to early somite stages in the pig, whereas they were found from early somite to mid‐somite stages in the rabbit; in both species cloacal membrane formation is complete prior to secondary neurulation. The results highlight the structural requirements for endoderm formation during development of the hindgut and suggest new mechanisms for the pathogenesis of common urogenital and anorectal malformations.