Ectoplasmic (“Junctional”) Specializations in Mammalian Sertoli Cells: Influence on Spermatogenic Cells^a

Parallel actin bundles and their multiple actin-bundling proteins

“…These intercellular junctions, which are believed to anchor and position spermatids throughout much of spermiogenesis [44,45], are perhaps the most neglected of all the parallel actin bundle containing structures. Found where Sertoli cells contact the head of an elongating spermatid, the ectoplasmic specialization is characterized ultrastructurally by its junctional plaque, which contains a thin layer of parallel actin bundles with hexagonally packed filaments sandwiched between the Sertoli cell plasma membrane and an affiliated flattened cistern of endoplasmic reticulum [44,45] (Figure 1e).…”

“…Found where Sertoli cells contact the head of an elongating spermatid, the ectoplasmic specialization is characterized ultrastructurally by its junctional plaque, which contains a thin layer of parallel actin bundles with hexagonally packed filaments sandwiched between the Sertoli cell plasma membrane and an affiliated flattened cistern of endoplasmic reticulum [44,45] (Figure 1e). The parallel actin bundles of the ectoplasmic specialization junctional plaque are believed to function in part as a scaffold that supports and stabilizes an adhesive domain in the Sertoli cell plasma membrane [44,45].…”

“…Found where Sertoli cells contact the head of an elongating spermatid, the ectoplasmic specialization is characterized ultrastructurally by its junctional plaque, which contains a thin layer of parallel actin bundles with hexagonally packed filaments sandwiched between the Sertoli cell plasma membrane and an affiliated flattened cistern of endoplasmic reticulum [44,45] (Figure 1e). The parallel actin bundles of the ectoplasmic specialization junctional plaque are believed to function in part as a scaffold that supports and stabilizes an adhesive domain in the Sertoli cell plasma membrane [44,45]. They are also believed to act indirectly, via their connection to the cistern of endoplasmic reticulum, as a link to an underlying network of microtubules that may be responsible for changes in the depth of the ectoplasmic specialization-spermatid complex within the seminiferous epithelium [45,46].…”

“…The parallel actin bundles of the ectoplasmic specialization junctional plaque are believed to function in part as a scaffold that supports and stabilizes an adhesive domain in the Sertoli cell plasma membrane [44,45]. They are also believed to act indirectly, via their connection to the cistern of endoplasmic reticulum, as a link to an underlying network of microtubules that may be responsible for changes in the depth of the ectoplasmic specialization-spermatid complex within the seminiferous epithelium [45,46]. Espin, the founding member of the espin family of actin-bundling proteins, was identified as a component of the parallel actin bundles in the ectoplasmic specialization junctional plaque …”

Actin bundling in plants

“…Recent data on the mechanisms underlying bundle formation indicate that animal cells use different combinations and sequences of actin-crosslinking proteins to assemble bundles with unique properties specific to their cellular functions [Bartles, 2000]. Indeed, at least two or three distinct actin-crosslinking proteins participate in the generation of highly specialized bundles found in neurosensory bristles of Drosophila [Tilney et al, 1995[Tilney et al, , 1996, as well as in brush border microvilli [Shibayama et al, 1987;Heintzelman and Mooseker, 1992], Drosophila nurse cells [Cant et al, 1994;Guild et al, 1997], hair cell stereocilia [Tilney et al, 1992], and sertoli cell ectoplasmic specializations [Russell and Peterson, 1985;Vogl et al, 1991]. Cooperative action of actin crosslinkers such as a-actinin and fascin has shown to significantly enhance the mechanical strength of cells [Tseng et al, 2005].…”