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Actin associated intercellular adhesion junctions in the mammalian testis

University of British Columbia

In the mammalian seminiferous epithelium, the cytoplasm of Sertoli cells adjacent to sites of intercellular attachment exhibits unique structural attributes. In each of these regions, a layer of hexagonally packed actin filaments lies situated between a cistern of endoplasmic reticulum and the plasma membrane. The filament layer together with the reticulum and adjacent plasma membrane are collectively termed an "ectoplasmic specialization". Ectoplasmic specializations occur in apical Sertoli cell regions at sites of attachment to spermatids and basally at sites of attachment to adjacent Sertoli cells. Ectoplasmic specializations have been hypothesized to be actin associated intercellular adhesion junctions. If this is true, molecular components that characterize actin associated adhesion junctions in general should be present in ectoplasmic specializations. In this study, I tested this prediction in two ways. First, I investigated whether or not the protein vinculin is co-distributed with actin filament bundles in ectoplasmic specializations of the ground squirrel. Second, I immunologically probed ectoplasmic specializations for three cell adhesion molecules (CAMs) that are commonly found in regions of intercellular adhesion in other tissues. My results indicate that vinculin is co-distributed with actin in Sertoli cell regions attached to spermatids. These data are consistent with the conclusion that vinculin is a component of ectoplasmic specializations and, therefore, with the hypothesis that the latter structures are a form of actin associated adhesion junction. Experiments using probes for the CAMs indicate that E-cadherin, A-CAM and N-CAM are probably not present in ectoplasmic specializations. The adhesion molecule at these sites may be a different member of the known CAMs or an as yet unidentified CAM. Based on data presented here and elsewhere indicating that ectoplasmic specializations are a form of actin associated adhesion junction, I describe the elaborate changes that occur in constituent filament bundles at sites of attachment to spermatids of the ground squirrel and interprete them in the context of the adhesion hypothesis. During the course of the co-localization studies described above, I observed that vinculin and actin are co-distributed at certain sites of intercellular attachment between interstitial cells of Leydig in the ground squirrel testis. Moreover, at the ultrastructural level I found these sites correspond to microfilament rich junction regions. These observations are consistent with the conclusion that actin associated intercellular adhesion junctions exist between interstitial cells of Leydig in the ground squirrel testis.

Text

2010-11-02

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http://hdl.handle.net/2429/29753

Anatomy, Cell Biology and Physiology

University of British Columbia

Graduate