Actin filaments associated with the basal Sertoli cell surface in the alligator and turtle

We have studied, using electron microscopy, the basal cytoplasm of Sertoli cells in the alligator (Alligator mississippiensis) and the turtle (Pseudemys scripta). Filament bundles occur immediately adjacent to the basal plasma membrane. The diameter of these filaments is smaller than that of perinuclear intermediate filaments, but is similar to that of filaments present in peritubular cells. In the alligator, the filament bundles appear to form a branching network over the base of the cell and are related to cisternae of the endoplasmic reticulum. In the turtle. filaments occur either in distinct bundles within folds of the plasma membrane or as a more uniform layer over the base of the cell. In fixed frozen sections, labelled with rhodamine phalloidin, linear bands of fluorescence occur in regions which correspond to those containing the filament bundles observed by electron microscopy. We conclude that the basal filaments in alligator and turtle Sertoli cells are actin and speculate that these filaments may be involved in cell/substratum adhesion.