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. Author manuscript; available in PMC: 2014 Jul 8.
Published in final edited form as: Int Rev Cell Mol Biol. 2013;301:291–358. doi: 10.1016/B978-0-12-407704-1.00006-3

Figure 6.1. Differences in the morphological layouts of junction types between a typical epithelium/endothelium and the seminiferous epithelium.

Figure 6.1

(A) For the junctional complex in typical epithelia/endothelia, TJs, which are responsible for sealing the intercellular space to create the barrier function by regulating paracellular and transcellular transport, are located at the apical region of the lateral membrane between adjacent epithelial/endothelial cells. Underneath TJs, there are AJs that contribute to most of the adhesive force of the apical junctional complex by connecting to a dense F-actin network, creating the zonula adherens plaque, to be followed by desmosomes. Both TJ and AJ are actin-based cell–cell anchoring junctions, whereas DS is intermediate filament-based cell–cell anchoring junction. Other junctional molecules such as GJs, which are not part of the junctional complex, are localized basal to the junctional complex (constituted by TJ, AJ and DS). (B) Unlike the junctional complex in typical epithelia which are furthest away from the basal lamina, the BTB in seminiferous epithelium is located near the basement membrane (a modified form of extracellular matrix in the testis). Instead of being arranged as discrete structure as in other epithelia/ endothelia, TJs, basal ES (a testis-specific actin-rich AJ) and GJs are coexisting at the BTB, which together with DS are all involved in creating the BTB. The BTB physically separates the seminiferous epithelium into the basal and apical (adluminal) compartments. Spermatogonia and preleptotene spermatocytes reside at the basal compartment, and preleptotene spermatocytes that arise at stage VII-VIII of the epithelial cycle in the rat testis are the only germ cells that can traverse the BTB. After traversing the BTB, spermatocytes undergo meiosis and eventually differentiate into elongating/elongated spermatids, and spermatids (step 8–19 spermatids in the rat testis) anchored to the Sertoli cells by apical ES. Furthermore, hemidesmosomes (intermediate filament-based cell–matrix anchoring junction) and focal adhesion complexes (FAC, or known as focal contacts, an actin-based cell–matrix anchoring junction) are also found in most epithelia, but FAC is absent in the seminiferous epithelium. Abbreviations used: Sg, spermatogonium; Sy, spermatocyte; rSp, round spermatid; eSp, elongating spermatid; ESp, elongated spermatid; Nu, Sertoli cell nucleus; DS, desmosome; AJ, adherens junction; GJ, gap junction; TJ, tight junction; ES, ectoplasmic specialization. For color version of this figure, the reader is referred to the online version of this book.