Institute for Developmental Biology, University of Cologne, Gyrhofstrabetae 17, 50931 Cologne, Germany.
Dev Biol. 2010 Apr 1;340(1):100-15. doi: 10.1016/j.ydbio.2009.12.034. Epub 2010 Jan 4.
As extra-embryonic tissues, the amnion and serosa are not considered to contribute materially to the insect embryo, yet they must execute an array of morphogenetic movements before they are dispensable. In hemimetabolous insects, these movements have been known for over a century, but they have remained virtually unexamined. This study addresses late extraembryonic morphogenesis in the milkweed bug, Oncopeltus fasciatus. Cell shape changes and apoptosis profiles are used to characterize the membranes as they undergo a large repertoire of final reorganizational events that reposition the embryo (katatrepsis), and eliminate the membranes themselves in an ordered fashion (dorsal closure). A number of key features were identified. First, amnion-serosa "fusion" involves localized apoptosis in the amnion and the formation of a supracellular actin purse string at the amnion-serosa border. During katatrepsis, a 'focus' of serosal cells undergoes precocious columnarization and may serve as an anchor for contraction. Lastly, dorsal closure involves novel modifications of the amnion and embryonic flank that are without counterpart during the well-known process of dorsal closure in the fruit fly Drosophila melanogaster. These data also address the long-standing question of the final fate of the amnion: it undergoes apoptosis during dorsal closure and thus is likely to be solely extraembryonic.
作为胚胎外组织，羊膜和浆膜不被认为对昆虫胚胎有实质性贡献，但在它们变得可有可无时，它们必须执行一系列形态发生运动。在不全变态昆虫中，这些运动已经被人们认识了一个多世纪，但它们几乎没有被研究过。本研究探讨了乳草虫，Oncopeltus fasciatus 的晚期胚胎外形态发生。细胞形状变化和细胞凋亡特征被用来描述膜，因为它们经历了一系列最终重组事件，使胚胎重新定位（katatrepsis），并以有序的方式消除膜本身（背侧闭合）。确定了一些关键特征。首先，羊膜-浆膜“融合”涉及羊膜中的局部细胞凋亡和羊膜-浆膜边界处超细胞层的肌动蛋白束的形成。在 katatrepsis 过程中，浆膜细胞的“焦点”经历过早的柱状化，可能作为收缩的锚点。最后，背侧闭合涉及羊膜和胚胎侧翼的新的修饰，在著名的果蝇 Drosophila melanogaster 背侧闭合过程中没有对应的修饰。这些数据还解决了羊膜最终命运的长期存在的问题：它在背侧闭合过程中发生细胞凋亡，因此很可能仅为胚胎外组织。
