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The acrosomal region of the spermatozoon of Ciona intestinalis: Its relationship with the binding to the vitelline coat of the egg

1985; Wiley; Volume: 11; Issue: 4 Linguagem: Inglês

10.1002/mrd.1120110405

1554-3919

Floriana Rosati, Maria Rosaria Pinto, Gianna Casazza,

Physiological and biochemical adaptations

Abstract This paper describes a study of the apical region of the spermatozoon of Ciona intestinalis before and during its binding to the vitelline coat of the egg. A combination of the techniques of thin sectioning, negative staining, and freeze fracture has revealed that in the apical‐most region, where a small acrosomal vesicle lies on the flat tip of the nucleus, there is a cap‐like region almost completely free of particles on the P face of the plasma membrane. The particle‐free area is surrounded by two circlets of orderly arranged particles. Upon binding to the vitelline coat the particles of the distal circlet show a partial displacement, while the particles of the apical circlet remain unaltered. The relationship between the apical circlet and the binding process is discussed. The final step of the acrosome reaction, which occurs in only a few of the bound spermatozoa, consists in the fusion of the plasma membrane with the acrosomal membrane, in the dehiscence of the acrosomal contents and finally in the formation of membrane tubules.