Cloney R A, Cavey M J
Cell Tissue Res. 1982;222(3):547-62. doi: 10.1007/BF00213854.
The larval tunic of Corella inflata is composed of two cuticular layers, extracellular filaments and ground substance. It lies outside the epidermis and most of it is known to be produced by the epidermis. The dorsal, ventral and caudal fins are specialized parts of the tunic that are essential for larval locomotion. The following hypothesis was tested: Morphogenesis of the larval fins is dependent upon the presence of extraembryonic structures (test cells, chorion or follicle cells) before completion of the late tail bud stage of development. We tested this by dechorionating embryos of Corella inflata and Ascidia paratropa. The operation removes all extraembryonic structures. It was performed mainly on neurula, early tail-bud and late tail-bud stages. Fin formation is inhibited when neurulae are dechorionated but not when late tail-bud or older embryonic stages are dechorionated. Dechorionated neurulae produce all of the major components of the tunic (cuticular layers, filaments and ground substance) but they are unable to form functional fins. At the time of dechorionation, in all experiments, the embryos had no fins. Removal of the follicle cells does not inhibit fin formation. The test cells are known to secrete granular "ornaments" that attach to the surface of the tunic. The fibrous, acellular chorion may serve to contain the test cells and their products or products of the embryo that are not firmly attached. The test cells may induce or control the morphogenesis of the larval fins in ascidians before the late tail-bud stage of development. We suggest ways of testing this hypothesis and an alternative hypothesis.
膨胀海鞘的幼虫被囊由两层角质层、细胞外细丝和基质组成。它位于表皮之外，已知其大部分由表皮产生。背鳍、腹鳍和尾鳍是被囊的特殊部分，对幼虫的运动至关重要。我们检验了以下假设：在发育的尾芽晚期完成之前，幼虫鳍的形态发生依赖于胚外结构（测试细胞、绒毛膜或卵泡细胞）的存在。我们通过去除膨胀海鞘和副热带海鞘的胚胎绒毛膜来进行检验。该操作去除了所有胚外结构。主要在神经胚、早期尾芽和晚期尾芽阶段进行。去除神经胚的绒毛膜会抑制鳍的形成，但去除晚期尾芽或更老胚胎阶段的绒毛膜则不会。去除绒毛膜的神经胚能产生被囊的所有主要成分（角质层、细丝和基质），但它们无法形成功能性的鳍。在所有实验中，去除绒毛膜时胚胎都没有鳍。去除卵泡细胞不会抑制鳍的形成。已知测试细胞会分泌附着在被囊表面的颗粒状“装饰”。纤维状的无细胞绒毛膜可能起到容纳测试细胞及其产物或胚胎中未牢固附着的产物的作用。测试细胞可能在发育的尾芽晚期之前诱导或控制海鞘幼虫鳍的形态发生。我们提出了检验这一假设的方法以及另一种假设。
