Cyclic modulation of sertoli cell junctional complexes in a seasonal breeder: The mink (Mustela vison)

Abstract

The development and modulation of Sertoli cell junctions was studied in newborn and adult mink during the active and inactive spermatogenic phases. The techniques used were electron microscopy of freeze‐fractured replicas and thin sections of tissues infused with horseradish peroxidase as a junction permeability tracer. In the newborn, freeze‐fractured developing junctions had either spherical or fibrillar particles. In addition, Junctional domains where particles were associated preferentially with the E‐face, and others where particles were associated preferentially with the P‐face, were found developing either singly or conjointly within a given membrane segment, thus yielding a heterogeneous Junctional segment. Coincidently with the development of a tubular lumen and the establishment of a competent blood‐testis barrier, Junctional strands were composed primarily of particulate elements associated preferentially with the E‐face. In adult mink during active spermatogenesis, cell junctions were found on the entire lateral Sertoli cell plasma membrane from the basal to the luminal pole of the cell. In the basal third of the Sertoli cell, membranous segments that faced a spermatogonium or a migrating spermatocyte displayed forming tight, gap, and adherens junctions. In the middle third, abutting membrane segments localized above germ cells were involved in continuous zonules and in adherens junctions. In the apical or luminal third, the zonules were discontinuous, and the association of Junctional particles with the E‐face furrow was lost. Gap junctions increased in both size and numbers. Junctional vesicles that appeared as annular gap and tight‐junction profiles in thin sections or as hemispheres in freeze‐fracture replicas were present. Reflexive tight and gap junctions were formed through the interaction of plasma membrane segments of the same Sertoli cell. Internalized Junctional vesicles were also present in mature spermatids. During the inactive spermatogenic phase, cell junctions were localized principally in the basal third of the Sertoli cell; Junctional strands resembled those of the newborn mink. During the active spermatogenic phase, continuous zonules were competent in blocking passage of the protein tracer. During the inactive phase the blood‐testis barrier was incompetent in blocking entry of the tracer into the seminiferous epithelium. It is proposed that modulation of the Sertoli cell zonules being formed at the base and dismantled at the apex of the seminiferous epithelium follows the direction of germ cell migration and opposes the apicobasal direction of junction formation reported for most epithelia. The arrest of spermatogenesis coincides with dramatic changes in the dynamic modifications of Sertoli cell zonules.