Three-dimensional structure of the Golgi apparatus in mouse spermatids: a scanning electron microscopic study

In this study, the three-dimensional organization of the Golgi apparatus in mouse spermatids was elucidated by preparing testicular tissue with the osmium-DMSO-osmium method and examining it by stereo-scanning electron microscopy. The cis-most saccule was found to be a regular network of anastomotic membranous tubules covered by a single cisterna of ER. The trans-Golgi network was seen to be composed of irregular saccules perforated by pores at the edge. It appears that the anastomosing trans-Golgi network breaks down into strings of connected vesicles which arise from the edge of the saccules during the cap phase of spermiogenesis. Many apparently individual vesicles seen in thin sections through the trans-Golgi network are actually joined in continuous strings. This was the first time that these structures could be visualized directly without three-dimensional image reconstruction. By correlating the morphology of the Golgi apparatus with the stage of acrosome formation, the Golgi cisternae were found to change dynamically in a cis-trans direction from fenestrated saccules to continuous strings of vesicles, which finally dissipated as transport vesicles at the trans aspect. This suggests that the hypothetical model of cisternal maturation, which dictates that cargo moves through the Golgi apparatus without leaving the cisternal lumen and the secretion occurs by progressive maturation of the Golgi cisternae as they move in the cis-trans direction, may be applicable to acrosome formation.