Comparative Electron and Light Microscopy of Early Spermatids during Mammalian Spermiogenesis

The aim of the study was to investigate the electron microscopic and microscopic features of spermatids at the late stages of spermiogenesis (acrosome phase and maturation phase) in mammals.

Material and methods. Material from seven mammalian species (domestic bull, ram, northern fur seal, sea otter, Eurasian beaver, mink, black-brown fox) was used. For electron microscopy, testis samples were fixed in 2.5% glutaraldehyde and 1% osmium fixative. Sections were prepared using BS-490 and LKB-4800 ultramicrotomes. The sections were stained with uranyl acetate and lead citrate and examined with a Tesla BS-500 electron microscope.

Results. During the acrosome phase, the nucleus elongates and assumes an elongated shape, while the cells change their orientation within the seminiferous tubule: they are positioned so that the acrosomic structure faces the basal membrane of the tubule. The acrosomal cap further develops into the acrosome. In the final maturation phase, mitochondria are arranged in a spiral pattern around the axoneme of the flagellar apparatus. In the caudal part of the elongated spermatid, the flagellar apparatus of the spermatozoon, which is the main component of the future sperm tail, is formed from the distal centriole.

Conclusion. At the late stages of spermiogenesis, chromatin condensation in the nucleus and acrosome formation are completed. By the end of spermiogenesis, the contact between late spermatids and Sertoli cells diminishes, and spermatozoa move into the lumen of the seminiferous tubule and subsequently into the epididymal duct.

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