The mechanism responsible for spermatid translocation in the mammalian seminiferous epithelium was proposed to be the microtubule-based transport of specialized junction

As developing sperm cells (spermatids) acquire an elongate shape during spermatogenesis, they become situated in invaginations in the apices of Sertoli cells. Initially, these crypts are shallow and spermatids are positioned in apical regions of the epithelium. As spermatogenesis continues, the crypts deepen. This deepening results in the repositioning of spermatid heads closer to the base of the epithelium. Still later, the crypts again become shallow and the spermatids are moved to the apex of the epithelium where they are eventually released. Although the biological significance of this ‘down and up’ translocation is not known, the mechanism responsible for the movement was proposed to be the microtubulebased transport of unique intercellular adhesion junctions (ectoplasmic specializations) that develop in Sertoli cell regions associated with the crypts (Vogl, 1988; Redenbach and Vogl, 1991). Ectoplasmic specializations, which develop in association with apical crypts, consist of the Sertoli cell plasma membrane in regions attached to spermatid heads, a layer of actin filaments and an attached cistern of endoplasmic reticulum (see Fig. 1A). The three components of the junction plaques are structurally very robust and together remain firmly adherent to spermatids when the latter cells are mechanically dissociated from the epithelium (Romrell and Ross, 1979; Vogl, 1996). A significant consequence of these features is that mechanical dissociation of spermatids from the epithelium can be used as a means of isolating intact junctions for use in experimental systems, and that the spermatid head can be used as a 2167 Journal of Cell Science 113, 2167-2176 (2000) Printed in Great Britain © The Company of Biologists Limited 2000 JCS1365