Changes in cytoskeletal actin patterns in the Malpighian tubules of the fleshfly,Sarcophaga bullata (Parker) (Diptera : Calliphoridae), during metamorphosis

Using the rhodamine-labelled phalloidin staining method in combination with detergent extraction, metamorphic changes in actin filament patterns were investigated in the Malpighian tubules of the fleshfly, Sarcophaga bullata (Parker) (Diptera : Calliphoridae). Metamorphosis in this organ implies a process of dedifferentiation, followed by a process of redifferentiation. During dedifferentiation, the large basal actin bundles of the primary cells disappear and the microvillar membrane surface of these cells decreases. Concomitantly, several vesicles are pinched off from infoldings of the brush border. In older pupae, the Malpighian tubules redifferentiate to give rise to adult tubules with actin patterns similar to those of larvae. During redifferentiation of the tubules, the secondary cells display a marked increase in the number of actin filaments in their protrusions. The primary cells in the distal part of the anterior Malpighian tubules of late pupae display a well-developed basal pattern of thick parallel actin bundles. In most cases, major changes in actin filament patterns are found simultaneously with major changes in cell shape, indicating a close relationship between these actin filaments and the process of cellular remodelling.