The Consequences of Actin Disruption at Sertoli Ectoplasmic Specialization Sites Facing Spermatids after in Vivo Exposure of Rat Testis to Cytochalasin D1

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Abstract
Cytochalasin D (CD) was used to perturb actin filaments of the Sertoli ectoplasmic specialization (ES)—a cytoskeletal complex of the Sertoli cell related to spermatids. CD (500 μM for 6 h) produced a loss of 88% of the ES facing the head region of early (Step 8) elongating spermatids as compared to vehicle (dimethyl-sulfoxide:saline) controls. Nitrobenzoxadiazole-phallacidin staining of F-actin revealed a CD-related loss of uniform fluorescence over the head of elongated spermatids. To examine for a possible relationship between the presence of actin and cell attachment at ES sites, hypertonic fixatives were introduced to provoke cell shrinkage and stress ES-associated junctions. After osmotic stress, cell-to-cell adhesion at ES sites remained intact in vehicle-treated animals. CD treatment caused Sertoli cells to separate from elon¬gating spermatids at sites where ES had been lost from the Sertoli cell surface. It is suggested that actin of the ES plays a role in cell-to-cell interaction analogous to its possible role at the Sertoli cell barrier. In CD-treated animals, structures resembling tubulobulbar complexes frequently developed at sites where ES was lost, suggesting that the loss of ES has a facilitatory role in tubulobulbar complex formation. It is hypothesized that tubulobulbar complexes are devices that rid the cells of ES-associated junctional links to effect dissociation of the spermatid from the Sertoli cell during spermiation. Spermatids at Step 8 of development are known to become oriented with their acrosomes facing the base of the Sertoli cell. After CD treatment, a 5.8-fold increase in malorientation of Step 8 spermatids was noted. A role for the ES cytoskeletal complex in orienting the spermatid acrosome toward the basal aspectof the Sertoli cell is also suggested.