Williams-Masson E M, Malik A N, Hardin J
Program in Cellular and Molecular Biology, University of Wisconsin, Madison 53706, USA.
Development. 1997 Aug;124(15):2889-901. doi: 10.1242/dev.124.15.2889.
The epiboly of the Caenorhabditis elegans hypodermis involves the bilateral spreading of a thin epithelial sheet from the dorsal side around the embryo to meet at the ventral midline in a process known as ventral enclosure. We present evidence that ventral enclosure occurs in two major steps. The initial migration of the hypodermis is led by a quartet of cells, which exhibit protrusive activity at their medial tips and are required to pull the hypodermis around the equator of the embryo. These cells display actin-rich filopodia and treatment with cytochalasin D immediately halts ventral enclosure, as does laser inactivation of all four cells. Once the quartet of cells has migrated around the equator of the embryo and approaches the ventral midline, the remainder of the leading edge becomes visible on the ventral surface and exhibits a localization of actin microfilaments along the free edges of the cells, forming an actin ring. Cytochalasin D and laser inactivation block ventral enclosure at this later stage as well and, based upon phalloidin staining, we propose that the second half of enclosure is dependent upon a purse string mechanism, in which the actin ring contracts and pulls together the edges of the hypodermal sheet at the ventral midline. The ventral cells then form junctions with their contralateral neighbors to complete ventral enclosure.
秀丽隐杆线虫皮下组织的外包涉及到一层薄上皮细胞从胚胎背侧开始双侧扩展，围绕胚胎并在腹侧中线处会合，这一过程称为腹侧封闭。我们提供的证据表明，腹侧封闭分两个主要步骤进行。皮下组织的初始迁移由一组四个细胞引导，这些细胞在其内侧尖端表现出突出活动，并且是拉动皮下组织围绕胚胎赤道所必需的。这些细胞显示出富含肌动蛋白的丝状伪足，用细胞松弛素D处理会立即停止腹侧封闭，对所有四个细胞进行激光灭活也会如此。一旦这组四个细胞围绕胚胎赤道迁移并接近腹侧中线，前缘的其余部分就会在腹侧表面可见，并在细胞的自由边缘沿肌动蛋白微丝呈现定位，形成一个肌动蛋白环。细胞松弛素D和激光灭活在这个后期阶段也会阻止腹侧封闭，并且基于鬼笔环肽染色，我们提出封闭的后半部分依赖于一种收缩环机制，即肌动蛋白环收缩并在腹侧中线处将皮下组织片的边缘拉拢在一起。然后腹侧细胞与其对侧邻居形成连接以完成腹侧封闭。
