SPATIALLY DYNAMIC INTERCELLULAR-ADHESION JUNCTION IS COUPLED TO A MICROTUBULE-BASED MOTILITY SYSTEM - EVIDENCE FROM AN IN-VITRO BINDING ASSAY

During spermatogenesis, spermatids change position in the seminiferous epithelium along an axis that is perpendicular to the seminiferous tu bule wall. During this period, spermatids are attached to apical invag inations of Sertoli cells. In areas of this attachment, unique junctio n plaques occur in Sertoli cells. These plaques consist of regions of the plasma membrane involved with intercellular adhesion, a layer of a ctin filaments that are hexagonally packed, and an underlying cistern of endoplasmic reticulum (ER). It previously has been proposed that th ese junction plaques, and therefore the attached spermatids, are trans located, by motor proteins, along microtubule tracts in the Sertoli ce ll. If this is true, microtubules should bind to the junction plaque i n a nucleotide dependent fashion. To verify this prediction, seminifer ous epithelia of the rat were separated from tubule walls and then mec hanically fragmented. These epithelial preparations were incubated, in both the presence and abence of 10 mM Mg(++)ATP, with exogenous micro tubules stabilized with taxol. Then unbound microtubules were separate d from microtubules bound to larger epithelial components by centrifug ing the samples through a step sucrose gradient. The fraction enriched for elongate spermatids was collected and processed for electron micr oscopy. The results indicate that the junction plaques remain attached to spermatids, the plaques are intact, and the cytoplasmic face of th e ER binds microtubules in a nucleotide dependent fashion. The results are consistent with the presence of motor proteins on the ER componen t of the junction plaques and with the general hypothesis of microtubu le-dependent spermatid translocation. (C) 1996 Wiley-Liss, Inc.