Observations on rat Sertoli ectoplasmic ('junctional') specializations in their association with germ cells of the rat testis.

The ectoplasmic ('junctional') specialization, a subsurface modification of the Sertoli cell that is often seen facing germ cells, was studied in relation to the development and maturation of these germ cells. This structure is composed of subsurface bundles of filaments and more deeply placed endoplasmic reticulum. The data indicate that these subsurface modifications of Sertoli cells are reutilized in a cyclic fashion, being transferred from their position facing late spermatids to one opposing less mature germ cells. Ectoplasmic specializations appeared to function mechanically in grasping the heads of the spermatids which are undergoing the elongation and maturation phases of spermiogenesis rather than in actually attaching Sertoli cells to these germ cells. It is postulated that the ectoplasmic specialization imparts rigidity to that area of the Sertoli cell that surrounds the head region of the germ cell, forming a recess and a mantle by which the germ cell may be moved toward the base or toward the surface of the seminiferous epithelium. The observed linkage of microtubules to the cisternae of the complex provided a morphological basis for the changes in the cytoarchietecture of the Sertoli cell, which must accompany these movements.