Desmosome‐like junctions between sertoli‐sertoli and sertoli‐germ cells in the ovotestis of Arion hortensis (Mollusca: Pulmonata)

AbstractThe ovotestis of Arion hortensis was investigated by electron microscopy, using serial ultrathin sections and freeze‐fracture. Desmosome‐like junctions between Sertoli‐Sertoli and Sertoli‐germ cells (spermatogonia, spermatocytes, spermatids, and spermatids just prior to spermiation) were studied. Desmosome‐like junctions were circular when viewed en face and 90‐‐180 nm in diameter. The intercellular space at the junctional site was 15–25 nm in width. An intermediate dense line was absent.Freeze‐fracture replicas showed that these junctions formed groups, with one to ten junctions within each group. Groups of junctions were scattered over the Sertoli cell surface. The most prominent feature of this junction was an electron‐dense plaque on the cytoplasmic face of the plasmalemma. We describe variation in the development of the electron‐dense plaque on the germ cell side at different stages in the development of the germ cell. In the spermatogonium and spermatocyte stages, desmosome‐like junctions had equally developed electron‐dense plaques. The plaques are pronounced in junctions between Sertoli cells and spermatocytes/spermatids and less developed in relation to late spermatids where nuclear condensation is complete, and appear to be lost at spermiation. Finger‐like processes arise from the Sertoli cell as desmosome‐like junctions are lost at spermiation.Hypertonic fixative solutions containing dextrose were applied to the ovotestis resulting in cell shrinkage. The intercellular space between Sertoli cells and germ cells was increased except where the desmosome‐like junctions were present. We suggest that desmosome‐like junctions provide strong adhesive sites between Sertoli and germ cells.