Anterior primitive endoderm may be responsible for patterning the anterior neural plate in the mouse embryo
Anterior primitive endoderm may be responsible for patterning the anterior neural plate in the mouse embryo
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DOI：
10.1016/s0960-9822(96)00753-1
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发表时间：
1996-11-01
期刊：
影响因子：
9.2
通讯作者：
Beddington, R
中科院分区：
文献类型：
--
作者：
Thomas, P;Beddington, R
背景资料：植入后，哺乳动物胚胎的基本身体平面在原肠胚形成期间建立，此时胎儿的上皮创始组织（外胚层）通过原始条纹侵入产生新组织。原条的形成确定了胚胎的尾侧，从而确定了前后轴。该轴的进一步图案化归因于由原始条纹产生的组织产生的信号，并且特别是位于胚胎中线沿着的中内胚层被认为负责神经外胚层的正确前后细分，因为它开始形成中枢神经系统（CNS）。原位杂交研究表明，含同源盒基因Hesx 1的表达开始与原条的形成一致，但发生在胚胎的另一侧，在前内胚层的一个小区域中。使用亲脂性荧光标记的谱系追踪显示，表达Hesx 1的第一个内胚层细胞并不注定对未来的胚胎有贡献，而是属于原始内胚层谱系，并且将被原肠胚形成期间由原条产生的定形内胚层所取代。在内胚层中首次检测到Hesx 1转录物后约24小时，它们开始出现在相邻的外胚层中，从而产生发育中的CNS的最前部成分，前脑，其继续表达Hesx 1。最终，Hesx1转录本只能在垂体开始发育的Rathke囊中检测到。在原肠胚形成的早期阶段去除表达Hesx 1的内胚层细胞可以防止或严重减少Hesx 1在外胚层和神经外胚层中的后期表达，但不影响发育中CNS尾部区域的基因表达。由于在任何轴向中内胚层形成之前，内脏胚胎内胚层中存在明显的前部模式，必须存在一种不依赖于原始条纹后代的赋予前部图案的机制。此外，正确的分子模式的最吻神经外胚层似乎取决于存在的前内脏胚胎内胚层在早期原肠胚形成。我们建议，原始内胚层是负责最初的诱导喙的身份在胚胎中，特别是正确的定义，未来的前脑神经外胚层。随后，在原肠胚形成过程中，当轴向中内胚层取代内脏胚胎内胚层时，这种身份将得到加强和维持。
Background: After implantation, the basic body plan of the mammalian embryo is established during gastrulation when the epithelial founder tissue of the fetus, the epiblast, gives rise to new tissues by ingression through the primitive streak. Formation of the primitive streak defines the caudal aspect of the embryo and thus the anteroposterior axis. Further patterning of this axis has been attributed to signals produced by tissues arising from the primitive streak, and in particular the mesendoderm located along the midline of the embryo is thought to be responsible for the correct anteroposterior subdivision of the neurectoderm as it begins to form the central nervous system (CNS).Results: In situ hybridization studies show that the onset of expression of the homeobox-containing gene Hesx1 coincides with the formation of the primitive streak, but occurs on the opposite side of the embryo, in a small domain of anterior endoderm. Lineage tracing using a lipophilic fluorescent label shows that the first endoderm cells to express Hesx1 are not destined to contribute to the future embryo, but instead belong to the primitive endoderm lineage and will be displaced by definitive endoderm arising from the primitive streak during gastrulation. Approximately 24 hours after Hesx1 transcripts are first detected in the endoderm, they start to appear in adjacent ectoderm that gives rise to the most anterior component of the developing CNS, the prosencephalon, which continues to express Hesx1. Eventually, Hesx1 transcripts are detectable only in Rathke's pouch as the pituitary starts to develop. Removal of endoderm cells expressing Hesx1 during the earlier stages of gastrulation either prevents or severely curtails the later expression of Hesx1 in ectoderm and neurectoderm, but does not affect gene expression in more caudal regions of the developing CNS.Conclusions: As overt anterior pattern is present in the visceral embryonic endoderm prior to formation of any axial mesendoderm, a mechanism for bestowing anterior pattern must exist which is independent of primitive streak descendants. Furthermore, correct molecular patterning of the most rostral neurectoderm appears to depend on the presence of this anterior visceral embryonic endoderm during the early stages of gastrulation. We propose that primitive endoderm is responsible for the initial induction of rostral identity in the embryo, and in particular for the correct definition of the future prosencephalic neurectoderm. Subsequently, this identity will be reinforced and maintained by axial mesendoderm when it displaces the visceral embryonic endoderm during the course of gastrulation.