Pfeiffer D C, Vogl A W
Department of Anatomy, Faculty of Medicine, University of British Columbia, Vancouver, Canada.
Anat Rec. 1993 Jan;235(1):33-50. doi: 10.1002/ar.1092350105.
Ectoplasmic specializations are complex actin-containing structures found at certain sites of intercellular attachment in Sertoli cells. Current evidence indicates that these structures are a form of actin-associated adhesion junction. In the turtle (Pseudemys scripta) and rooster (Gallus domesticus) ectoplasmic specializations are known to occur adjacent to sites of attachment to elongate spermatids and are characterized by a layer of "loosely" cross-linked actin filaments that lies next to the plasma membrane. In the turtle, a cistern of endoplasmic reticulum is associated with the cytoplasmic face of the filament layer. We have found that, in fixed frozen sections of turtle and rooster testes, immunological probes for myosin II react with epithelial regions that also stain with probes for filamentous actin and that are known to be sites at which ectoplasmic specializations occur. Furthermore, when exposed to standard contraction buffers, the diameters of glycerinated ectoplasmic specializations of the turtle are statistically smaller than those of the same structures exposed to control buffers. We interpret these smaller diameters as being produced by the contraction of actin bundles within the ectoplasmic specializations. Our results indicate that ectoplasmic specializations in the rooster and turtle, unlike those in mammals, possess contractile properties. We speculate that ectoplasmic specializations in eutherian mammals may have evolved from actin-associated adhesion junctions in which the actin bundles were initially contractile and from which myosin II was secondarily lost.
胞质特化结构是在支持细胞的细胞间附着特定部位发现的含有肌动蛋白的复杂结构。目前的证据表明，这些结构是一种与肌动蛋白相关的黏附连接形式。在乌龟（伪彩龟）和公鸡（家鸡）中，已知胞质特化结构出现在与延长的精子细胞附着部位相邻处，其特征是紧邻质膜有一层“松散”交联的肌动蛋白丝。在乌龟中，内质网池与丝层的细胞质面相关联。我们发现，在乌龟和公鸡睾丸的固定冰冻切片中，肌球蛋白II的免疫探针与上皮区域发生反应，这些区域也能用丝状肌动蛋白探针染色，并且已知是胞质特化结构出现的部位。此外，当暴露于标准收缩缓冲液时，乌龟甘油化的胞质特化结构的直径在统计学上小于暴露于对照缓冲液的相同结构的直径。我们将这些较小的直径解释为胞质特化结构内肌动蛋白束收缩产生的结果。我们的结果表明，与哺乳动物不同，公鸡和乌龟的胞质特化结构具有收缩特性。我们推测，真兽类哺乳动物的胞质特化结构可能是从与肌动蛋白相关的黏附连接进化而来的，在这种连接中，肌动蛋白束最初具有收缩性，随后肌球蛋白II丢失。
