Ectoplasmic specializations in the Sertoli cell: new vistas based on genetic defects and testicular toxicology

Abstract The ectoplasmic specialization is a unique junctional complex formed in two cortical areas of the Sertoli cell in the mammalian testis: one near the base of the seminiferous epithelium forming the blood-testis barrier, and the other near the lumen of the seminiferous tubule embracing the acrosome region of the developing spermatids. The specialization consists of the Sertoli cell plasma membrane, a subsurface cistern of the endoplasmic reticulum and a layer of closely packed actin filaments that is sandwiched between the plasma membrane and the subsurface cistern. No functions of the specializations other than the blood-testis barrier have been established. However, over the past decade, knowledge about the ectoplasmic specialization has been steadily accumulating and, in particular, there has been a tremendous increase in knowledge based on molecular biological approaches to specialization-associated proteins, including tight junction-associated proteins, based on phenotype analyses of gene-knockout mice and mutant animals, and based on analyses of the effects of exogenous estrogens, so-called endocrine disruptors. Progress in studies on the ectoplasmic specialization will facilitate the elucidation of numerous important questions regarding spermatogenesis, including the pathogenesis of azoospermia and the mechanisms of action of endocrine disruptors.