Rhombomere transplantation repatterns the segmental organization of cranial nerves and reveals cell-autonomous expression of a homeodomain protein.
Rhombomere transplantation repatterns the segmental organization of cranial nerves and reveals cell-autonomous expression of a homeodomain protein.
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菱形移植重新塑造了脑神经的节段组织并揭示了同源域蛋白的细胞自主表达。
作者：
Shigeru Kuratani;Gregor Eichele
发育中的脊椎动物后脑由节段单位组成，称为菱节。后脑神经外胚层表达3' Hox 1和2簇基因的特征模式，其表达的前限与菱形边界一致。一种特殊的Hox基因，称为Ghox 2.9，最初在整个后脑中表达，直到菱形节4（r4）的前缘。后来，Ghox 2.9在r4中强烈上调，并且Ghox 2.9蛋白在r4的所有神经外胚层细胞和来自该菱形节的舌骨嵴细胞群中被发现。使用多克隆抗体，将r4移植到后脑内后，对Ghox 2.9进行免疫定位。无论r4移植到哪里，Ghox 2.9的表达都是细胞自主的，无论是在移植物的神经外胚层还是在移植物来源的舌骨嵴细胞群中。在所有的脊椎动物中，菱形体和颅神经（神经V，VII+VIII，IX，X）表现出刻板的关系：神经V出现在r2的水平，神经VII+VIII在r4和神经IX-X延伸到尾部的r6。为了研究菱形体移植如何影响这种模式，用单克隆抗体E/C8（用于观察PNS和偶数菱形体）和HNK-1（用于检测嵴细胞和奇数菱形体）对手术胚胎进行染色。在移植后，菱形没有改变E/C8或HNK-1的表达或其产生嵴细胞的能力。例如，移植的r4产生了嵴细胞的侧流，而与移植部位无关。此外，在发育后期，异位r4形成了额外的颅神经根。相反，将r3（缺乏嵴细胞）移植到r7区域导致宿主神经根形成的抑制。这些研究结果强调，在脊神经分割，这完全取决于体节的模式，颅神经图案所带来的内在因素菱形和附着的神经嵴细胞群。神经外胚层和PNS的模式在后脑发育的早期被指定，并且不能受到组织移植的影响。所观察到的Ghox 2.9（也可能是其他Hox基因）的细胞自主表达为Hox基因表达至少部分地是后脑神经外胚层内节段性特化的基础这一观点提供了进一步的证据。
The developing vertebrate hindbrain consists of segmental units known as rhombomeres. Hindbrain neuroectoderm expresses 3' Hox 1 and 2 cluster genes in characteristic patterns whose anterior limit of expression coincides with rhombomere boundaries. One particular Hox gene, referred to as Ghox 2.9, is initially expressed throughout the hindbrain up to the anterior border of rhombomere 4 (r4). Later, Ghox 2.9 is strongly upregulated in r4 and Ghox 2.9 protein is found in all neuroectodermal cells of r4 and in the hyoid crest cell population derived from this rhombomere. Using a polyclonal antibody, Ghox 2.9 was immunolocalized after transplanting r4 within the hindbrain. Wherever r4 was transplanted, Ghox 2.9 expression was cell-autonomous, both in the neuroectoderm of the graft and in the hyoid crest cell population originating from the graft. In all vertebrates, rhombomeres and cranial nerves (nerves V, VII+VIII, IX, X) exhibit a stereotypic relationship: nerve V arises at the level of r2, nerve VII+VIII at r4 and nerves IX-X extend caudal to r6. To examine how rhombomere transplantation affects this pattern, operated embryos were stained with monoclonal antibodies E/C8 (for visualization of the PNS and of even-numbered rhombomeres) and HNK-1 (to detect crest cells and odd-numbered rhombomeres). Upon transplantation, rhombomeres did not change E/C8 or HNK-1 expression or their ability to produce crest cells. For example, transplanted r4 generated a lateral stream of crest cells irrespective of the site into which it was grafted. Moreover, later in development, ectopic r4 formed an additional cranial nerve root. In contrast, transplantation of r3 (lacks crest cells) into the region of r7 led to inhibition of nerve root formation in the host. These findings emphasize that in contrast to spinal nerve segmentation, which entirely depends on the pattern of somites, cranial nerve patterning is brought about by factors intrinsic to rhombomeres and to the attached neural crest cell populations. The patterns of the neuroectoderm and of the PNS are specified early in hindbrain development and cannot be influenced by tissue transplantation. The observed cell-autonomous expression of Ghox 2.9 (and possibly also of other Hox genes) provides further evidence for the view that Hox gene expression underlies, at least in part, the segmental specification within the hindbrain neuroectoderm.
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