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Sertoli cell microtubules: their polarity and binding to spermatid associated ectoplasmic specializations Redenbach, Darlene Marie


During spermatogenesis, spermatogenic cells are moved through the blood testis barrier from the basal to the apical compartment, where they become oriented parallel to the long axis of the Sertoli cell, and situated within Sertoli cell crypts. They are moved again toward the base of the epithelium, before being translocated across the epithelium for release into the tubule lumen. Crypts are lined with unique actin containing submembrane structures called ectoplasmic specializations (ESs) that form part of the Sertoli cell-spermatid junction. ESs consist of the Sertoli cell membrane, a fenestrated cistern of smooth endoplasmic reticulum, and a highly ordered intervening array of actin filaments. ESs are thought to participate in establishing junctional domains at Sertoli cell-spermatid adhesion junctions, which serve to anchor the developing spermatids within the Sertoli cell crypts. Sertoli cell microtubules occur adjacent to the endoplasmic reticulum of the ES (ESER), oriented parallel to the long axis of the cell, and to the direction of spermatid translocation. Other investigators have described linkages between the ESER and adjacent microtubules. Sertoli cell microtubules have been suggested to aid in orientation and positioning of spermatogenic cells, within the seminiferous epithelium. It is proposed that this may be achieved by a microtubule-based transport mechanism known to be involved in establishing and maintaining organelle positioning in other cells. As part of a study to test the hypothesis that spermatid translocation is a microtubule-based event, the polarity of Sertoli cell microtubules was determined. The potential for binding between spermatid-ESs and microtubules was assayed, and the binding characterized, using a selection of conditions known to alter organelle-microtubule interaction in other systems. The results of this study indicate that Sertoli cell microtubules are orientated with their minus-end directed toward the apical surface of the cell and that microtubules bind to spermatid-ES complexes, are releasable in the presence of nucleotides, and share binding properties with known mechanoenzymes. These results are consistent with the hypothesis that spermatids are moved through the seminiferous epithelium by a microtubule-based transport mechanism.

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