Bergquist P R, Glasgow K
Exp Biol. 1986;45(2):111-22.
The fate of the ciliated epithelium of sponge larvae at metamorphosis has been the subject of debate for many years. In order to resolve the phylogenetic position of the Porifera it must be determined whether these cells migrate inwards to become adult choanocytes or are lost at metamorphosis. We report an approach to this problem by observing metamorphosing larvae using electron microscopy and by assaying the aggregation potential of ciliated and central larval cells fractionated on Percoll gradients. Our results indicate that larval epithelial cells are phagocytosed during metamorphosis and that they do not have aggregation capability. The latter is essential to permit choanocyte chamber formation. Larval archaeocytes do possess aggregation capability. We argue that larval ciliated cells are dispersal effectors only and are terminally differentiated. Thus 'inversion of layers' as claimed by earlier authors does not occur. These results are discussed in relation to the role of aggregation facilitating systems and to the structure of sponge larvae.
多年来，海绵幼虫变态时纤毛上皮细胞的命运一直是争论的焦点。为了确定多孔动物门的系统发育位置，必须确定这些细胞是向内迁移成为成体领细胞，还是在变态过程中消失。我们报告了一种解决该问题的方法，即使用电子显微镜观察变态幼虫，并检测在Percoll梯度上分离的纤毛幼虫细胞和中央幼虫细胞的聚集潜能。我们的结果表明，幼虫上皮细胞在变态过程中被吞噬，并且它们没有聚集能力。而后者对于形成领细胞腔至关重要。幼虫原始细胞确实具有聚集能力。我们认为幼虫纤毛细胞仅仅是扩散效应器，并且已经终末分化。因此，早期作者所声称的“层反转”并未发生。本文结合聚集促进系统的作用和海绵幼虫的结构对这些结果进行了讨论。
