Distribution of actin in spermatids and adjacent Sertoli cell regions of the rat.

In this study, we describe the distribution of actin filaments in and around spermatids that are mechanically dissociated, in the presence and absence of exogenous trypsin, from the seminiferous epithelium of the rat. NBD-phallacidin and subfragment 1 of the myosin molecule (S-1) are used as probes for filamentous actin at the light and electron microscopic levels, respectively. The fluorescence associated with spermatids mechanically dissociated in the absence of trypsin is due to actin both in the spermatogenic cells themselves and in attached Sertoli cell ectoplasmic specializations. Fluorescence generated by labelled actin in ectoplasmic specializations occurs in linear tracts that follow the outer contour of spermatid heads. The residual fluorescence seen when trypsin is used to detach Sertoli cell fragments is diffuse and due to f-actin in the subacrosomal space. Electron microscopic data agree with the fluorescence results. This study conclusively demonstrates that Sertoli cell ectoplasmic specializations remain attached to spermatids mechanically dissociated from the seminiferous epithelium. This observation may be useful when attempting to isolate ectoplasmic specializations for biochemical analyses.