Serial block-face scanning electron microscopy reveals neuronal-epithelial cell fusion in the mouse cornea
Serial block-face scanning electron microscopy reveals neuronal-epithelial cell fusion in the mouse cornea
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DOI：
10.1371/journal.pone.0224434
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发表时间：
2019-11-13
期刊：
影响因子：
3.7
通讯作者：
Burns, Alan R.
中科院分区：
文献类型：
--
作者：
Courson, Justin A.;Smith, Ian;Burns, Alan R.
角膜是人体内神经支配最强的组织。普遍认为角膜基质神经穿透上皮基底层，产生上皮内神经。在我们对小鼠角膜神经成像的研究过程中，我们观察到一种新的神经元-上皮细胞相互作用，其中接近角膜上皮的神经与基底上皮细胞融合，使得它们的质膜是连续的，神经元轴浆自由地覆盖上皮细胞质。在这项研究中，我们试图确定的频率，分布和形态学的角膜内的神经元上皮细胞融合事件。从8-10周龄C57 BLI 6 J小鼠的角膜缘和中央角膜中的前基质获得连续电子显微镜图像。我们发现了一种新的替代行为的证据，涉及神经元-上皮相互作用，其中42.8%的中央角膜神经束接近上皮含有轴突与基底上皮细胞融合。穿入神经的平均表面积与体积比为3.32，而融合神经的平均表面积与体积比为1.39（p < 0.0001）。尽管如此，这两个神经元上皮细胞的相互作用涉及类似大小的不连续性的基底层。为了验证融合的神经元和上皮细胞之间的质膜连续性，我们使用亲脂性膜示踪剂Dil。大多数的角膜神经与Dil标记后，应用到三叉神经节，并与我们的超微结构观察一致，融合位点被认为是Dil标记的基底上皮细胞位于基质神经终止点。这些研究提供的证据表明，神经元-上皮细胞融合是主要发生在中央角膜中的细胞-细胞相互作用，并且融合的神经束在形态上不同于穿透的神经束。据我们所知，这是文献中首次描述神经元-上皮细胞融合，为目前对角膜神经支配的理解增加了新的复杂性。
The cornea is the most highly innervated tissue in the body. It is generally accepted that corneal stromal nerves penetrate the epithelial basal lamina giving rise to intra-epithelial nerves. During the course of a study wherein we imaged corneal nerves in mice, we observed a novel neuronal-epithelial cell interaction whereby nerves approaching the epithelium in the cornea fused with basal epithelial cells, such that their plasma membranes were continuous and the neuronal axoplasm freely abutted the epithelial cytoplasm. In this study we sought to determine the frequency, distribution, and morphological profile of neuronal-epithelial cell fusion events within the cornea. Serial electron microscopy images were obtained from the anterior stroma in the paralimbus and central cornea of 8-10 week old C57BLI6J mice. We found evidence of a novel alternative behavior involving a neuronal-epithelial interaction whereby 42.8% of central corneal nerve bundles approaching the epithelium contain axons that fuse with basal epithelial cells. The average surface-to-volume ratio of a penetrating nerve was 3.32, while the average fusing nerve was smaller at 1.39 (p < 0.0001). Despite this, both neuronal-epithelial cell interactions involve similarly sized discontinuities in the basal lamina. In order to verify the plasma membrane continuity between fused neurons and epithelial cells we used the lipophilic membrane tracer Dil. The majority of corneal nerves were labeled with Dil after application to the trigeminal ganglion and, consistent with our ultrastructural observations, fusion sites recognized as Dil-labeled basal epithelial cells were located at points of stromal nerve termination. These studies provide evidence that neuronal-epithelial cell fusion is a cell-cell interaction that occurs primarily in the central cornea, and fusing nerve bundles are morphologically distinct from penetrating nerve bundles. This is, to our knowledge, the first description of neuronal-epithelial cell fusion in the literature adding a new level of complexity to the current understanding of corneal innervation.