Locke M, Huie P
Tissue Cell. 1981;13(4):787-803. doi: 10.1016/s0040-8166(81)80014-6.
Epidermal cells in insect integumental epithelia develop branched cytoskeletal extensions or feet at their base that are similar in appearance to the processes put out by cells in tissue culture. We have developed a procedure to show the feet that gives an effect as if thousands of cells randomly arranged in the epithelium had each been injected with lead salt visualized as black lead sulphide. The procedure depends upon the fact that after brief glutaraldehyde fixation, tannic acid only penetrates some cells where it mordants lead ions and binds osmium. Individual cells visualized in this manner show their outlines as if they are separate in a tissue culture although they are part of a closely packed epithelium. The feet are metamorphic structures formed after pupal commitment and are necessary for metamorphic changes in segment shape. In Calpodes larvae the feet are orientated axially in the direction of the segmentally repeating gradient and may extend for several cell diameters. They extend under the influence of low titres of 20-hydroxyecdysone such as those occurring in the intermoult. When stimulated by high titres like those in pre-pupae, the feet contract at the same time as the segments shorten to pupal proportions. We believe that cell processes like the epidermal feet are ubiquitous but that they have often been overlooked because of the difficulty of demonstrating the outlines of single cells that are united in epithelia.
昆虫体表上皮中的表皮细胞在其基部会发育出分支状的细胞骨架延伸结构或足，其外观与组织培养中细胞伸出的突起相似。我们开发了一种方法来显示这些足，其效果就好像上皮中随机排列的数千个细胞每个都被注入了铅盐，并可视化为黑色硫化铅。该方法基于这样一个事实：在经过短暂的戊二醛固定后，单宁酸只会穿透一些细胞，在这些细胞中它会媒染铅离子并结合锇。以这种方式可视化的单个细胞显示出它们的轮廓，就好像它们在组织培养中是分开的，尽管它们是紧密排列的上皮的一部分。这些足是在蛹期确定后形成的变态结构，对于体节形状的变态变化是必需的。在角纹蛾幼虫中，这些足沿轴向排列在节段重复梯度的方向上，可能会延伸几个细胞直径。它们在低滴度的20-羟基蜕皮激素的影响下延伸，例如在蜕皮间期出现的那些。当受到像预蛹期那样的高滴度刺激时，足会在体节缩短到蛹的比例的同时收缩。我们认为像表皮足这样的细胞突起是普遍存在的，但由于难以显示上皮中联合在一起的单个细胞的轮廓，它们常常被忽视。
