Evolution of the Apical Body in Golden Hamster Spermatids With Some Reference to Primates

Abstract

The development of the "apical body" was followed at the electron microscope level in spermatids of the golden hamster. As the cap-shaped acrosome is formed it is separated from the nucleus by a thin layer of fine flocculent material. The layer is commonly termed the subacrosomal space. Small whorls of membrane were found in the apical region of the subacrosomal space of hamster spermatids during the cap and acrosome phases of spermiogenesis. In the final or maturation phase of spermiogenesis the membrane whorls appear larger and are present in the apical subacrosomal space in greater numbers. A dense coarse granular material was found together with the membrane whorls in several instances. This material replaces the whorled membrane structures by the completion of spermiogenesis, becomes more amorphous in appearance and in the mature sperm represents the apical body. In late spermatids of the golden hamster the relatively dense apical body and some of the fine flocculent material of the subacrosomal space become extended to one side beyond the apex of the nucleus, there representing the classical "rod" or "perforatorium." Whorls of membrane were occasionally found in the apical subacrosomal space of late spermatids of monkeys and a minute and more amorphous body of material (apical body?) was discerned in a few rhesus spermatids undergoing spermiation. In view of observations by others of membrane whorls in the subacrosomal space of late spermatids of the rabbit, mouse and Norwegian lemming, and of an apical body in spermatozoa of the rabbit, guinea pig and human, it is suggested that the process of differentiation of an apical body observed in hamster spermatids may occur in other mammalian species.