The effects of brefeldin A on acrosome formation and protein transport to the acrosome in organ cultures of rat seminiferous tubules.

To investigate the contribution of vesicular transport to acrosome formation, we examined the effect of brefeldin A (BFA), a potent inhibitor of membrane traffic, on the ultrastructural changes of the organella in early spermatids. The experiments were done in an organ culture system of rat seminiferous tubules. After exposure to BFA, the fuzzy-coated projections of the endo-plasmic reticulum (ER) cisternae directing toward the Golgi stack disappeared. The Golgi stacks were also disrupted, forming numerous small vesicles and tubular networks. The head-cap was fragmented in step 4-7 spermatids. We also investigated the effect of BFA on protein transport to the acrosome by using a monoclonal antibody to the acrosomal protein MN7 (mMN7) as a model. After a 5-h exposure, the mMN7 immunoreactivity was absent from the developing acrosomic system in step 2-3 spermatids. These results indicate that BFA blocks the vesicular transport, causing an insufficient supply of acrosomal materials to the acrosome, which eventually leads to abnormal acrosome formation in early spermiogenesis.