In Sertoli cells. In the testis, Sertoli cells share a morphological feature found in cells of most epithelia: they possess a layer of subsurface or cortical actin that occupies the peripheral cytoplasm and surrounds the perimeter of the cell. In the Sertoli cells, this cortical or peripheral actin is typically sandwiched between cisternae of endoplasmic reticulum (ER) on the intracellular side and the plasma membrane on the extracellular side. Within the Sertoli cell, the monomeric form of actin has been reported in the base, the middle, and the apex, while the filamentous form has been shown in the base and the apex of the cell. Thus, G-actin was localized in the same sites as F-actin, but, in addition, the monomeric actin was found in sites where F-actin was not detectable.
The finding of scinderin in the same sites as cortical G- and F-actin may reflect the role this actin regulatory protein plays on the perijunctional actin filament network that accompanies and possibly influences the function of the Sertoli cell junctions. The use of cytochalasin D and/or of ZO-toxin of cholera, two actin-depolymerizing agents, induces a disruption of perijunctional actin filaments followed by a breakage of the paracellular barrier, suggesting a functional link between actin organization and the tight junction. By analogy with the muscle, the subsurface cisternae of ER that accompany Sertoli cell junctions near the base (joining adjacent Sertoli cells) and the apex (joining Sertoli cells and spermatids) of the epithelium are probably involved in the regulation of local Ca2+ ion concentration in selected regions of the Sertoli cells.