VARIATIONS IN THE STRUCTURAL CHARACTER AND STABILITY OF THE NUCLEAR CHROMATIN IN MORPHOLOGICALLY NORMAL HUMAN SPERMATOZOA

Abstract

Summary. Decondensation of the nuclear chromatin of mammalian spermatozoa can be induced by treatment with sodium dodecyl sulphate (SDS) containing dithiothreitol (DTT)—a reagent which specifically cleaves -S-S- crosslinks. The nuclei of mature rabbit and monkey spermatozoa respond to SDS/DTT treatment in a uniform manner, each expanding to a similar degree, whereas those of the treated human ejaculate display a consistent heterogeneity between individual spermatozoa in their degree of decondensation which is unrelated to head shape. A variable proportion of the sperm nuclei from human ejaculates will swell in SDS alone and correlated ultrastructural studies indicate that these probably possess incompletely condensed chromatin of granular appearance. The heterogeneity of sperm nuclei in the human ejaculate revealed by combined treatment with SDS/DTT, on the other hand, is probably not visible at the ultrastructural level before such treatment. The decondensation induced by SDS/DTT allows detection of nuclear vacuoles which are not evident with the light microscope in intact spermatozoa. Such vacuoles were present in >90% of the spermatozoa of one individual whose ejaculate was otherwise normal. The finding that human sperm nuclei of normal shape may vary considerably with respect to the character of their chromatin raises several questions; these include the aetiology and molecular basis of such heterogeneity and the possible bearing these differences might have on the early development of the human embryo. The present technique of controlled nuclear decondensation provides a simple method by which the structural quality of sperm nuclei can be assessed.