Nuclear status of human sperm cells by transmission electron microscopy and image cytometry: changes in nuclear shape...

Computer-assisted transmission electron microscopy (TEM) image cytometry was used to investigate changes in nuclear shape and chromatin texture of human sperm during normal spermiogenesis and epididymal transit. Analysis was performed on a large series of micrographs of longitudinal sections of nuclei from spermatids and epididymal caput and cauda sperm. Thirteen parameters characterizing nuclear shape and chromatin texture were measured. Quantitative data showed that from early spermiogenesis to the end of epididymal transit, a decrease in nuclear area and width occurred concomitantly with not only an increase in chromatin condensation but also an increase in heterogeneity of the degree of condensation. The oriented spatial arrangement of chromatin along the major nuclear axis as measured by gradient parameters indicated that in humans, condensation of chromatin begins in the posterior pole and proceeds apically; this is an important difference between humans and other mammalian species. Most parameters did not differ substantially in sperm from testis and caput epididymis, but did change as the cells moved from the caput to the cauda epididymis, indicating completion of nuclear maturation. Discriminant functions of basic parameters, as followed by canonical transformation and cluster representation, automatically classified the nuclei in a sequence that was found to concur with the biological maturation sequence during normal spermiogenesis and epididymal transit.