Ultrastructual studies on maturing spermatids and on sertoli cells in the bandicoot Perameles nasuts Geoffroy (Marsupialia)

Abstract

This paper describes maturation changes in bandicoot spermatids after the latter have become embedded in Sertoli cells and are orientated within the seminiferous tubule. The changes are recorded as taking place in four stages, namely the stage of nuclear flattening and condensation, the stage of nuclear rotation, and the early and late post-rotational stages. The changes in shape and reduction in volume of the nucleus taking place during these stages are described, together with the division of the nuclear contents into condensed chromatin and the less electron-dense parachromatin. The disposition of nuclear pores in relation to the distribution of these two substances is discussed. A possible means of the disposal of redundant nuclear envelope substance is outlined. An account of the modifications taking place in the structures of the neck region is given and it is shown that both transverse and longitudinal centrioles persist until the terminal stages of spermiogenesis, when the latter centriole disappears. As a result of the migration of the annulus and the attached proximal extremity of the cytoplasmic canal, the axial filament complex of the future middle piece is left in contact with the general spermatid cytoplasm, and thus is created a pathway whereby spermatid mitochondria can migrate to this part of the complex to form the mitochondria1 sheath of the middle piece. Details are presented of the changes in form, throughout spermiogenesis, of spermatid mitochondria as well as of the acrosome, manchette, and nuclear ring. A description is given of specialized changes in that part of Sertoli cell cytoplasm immediately adjacent to the spermatid acrosome. It is thought that these changes are indicative, and mark out the extent, of a Sertoli cell-spermatid attachment. Cyclic changes in the overall form as well as in the endoplasmic reticulum and mitochondria of Sertoli cells are recorded. Pinocytotic activity in Sertoli cells and spermatids, as well as secretory activity in Sertoli cells, is examined.