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Actin-related intercellular adhesion junctions in vertebrate Sertoli cells Pfeiffer, David Carl


In the eutherian mammal seminiferous epithelium, the cytoplasm of Sertoli cells adjacent to certain regions of intercellular attachment exhibits unusual structural complexes. At these sites, a layer of non-contractile, hexagonally packed actin filaments is positioned between the Sertoli cell plasma membrane and an underlying cistern of endoplasmic reticulum. The filament layer along with the endoplasmic reticulum and the plasma membrane involved with attachment are referred to as an "ectoplasmic specialization". Ectoplasmic specializations are found apically at sites of attachment to spermatids and basally at sites of attachment to neighboring Sertoli cells. Similarly structured complexes are not found in other cell types nor in Sertoli cells of other vertebrate species. Ectoplasmic specializations of eutherian mammals have been hypothesized to be a highly specialized form of actin-related adhesion junction. If this is true, then non-mammalian homologues of this junction should be present and, in general, should more closely resemble typical actin-related adhesion junctions found in other cell types than do mammalian ectoplasmic specializations. I have tested this prediction by conducting a systematic comparative survey of the morphology and composition of actin-related adhesion junctions in Sertoli cells of non-mammalian vertebrates. My results indicate that vertebrate Sertoli cells use actin-related adhesion junctions as a common mechanism for adhesion to elongating spermatids and to neighboring Sertoli cells. In non-mammalian vertebrate classes, the junctions appear to possess contactile properties and, in general, more closely resemble the actin-related adhesion junctions of other cell types then do eutherian ectoplasmic specializations. Structural differences in the junctions between classes indicate that different strategies for intercellular adhesion have evolved at these sites within various vertebrate classes. These data suggest that eutherian mammal ectoplasmic specializations represent a modified form of actin-related adhesion junction. I speculate on what the precursors of the present-day eutherian junctions may have been like as well as on how and why structural adaptations may have occurred at these sites.

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