ULTRASTRUCTURE OF NUCLEAR CONDENSATION AND LOCALIZATION OF DNA AND PROTEINS IN SPERMATOZOA OF A DASYURID MARSUPIAL, SMINTHOPSIS-CRASSICAUDATA

In the dasyurid marsupial, Sminthopsis crassicaudata, the mature sperm atozoon has an inner homogeneous (C1) and a peripheral indented (C2) r egion. Using DNase-gold conjugates, and biotinylated genomic DNA probe s, DNA was found to occur in both C1 and C2 regions. The morphogenesis of the spermatozoon nucleus was investigated using ultrastructural an d cytochemical studies. Spermiogenesis was divided into 15 steps. By s tep 10, condensation of the C1 region was complete, and at the caudal extremity of the spermatid nucleus, the nuclear envelope enclosed an e lectron-lucent space. This space and the surrounding nuclear envelope became very enlarged at step 11. At this stage, a plate of approximate ly 70 nm in thickness was present along the caudal segment of the C1 r egion; this ''nuclear mantle'' did not bind DNase-gold conjugates but stained for lysine-rich proteins using alcoholic phosphotungstic acid. Chromatin condensation resumed at step 12 with the appearance of sphe rical chromatin structures peripheral to the C1 chromatin. These struc tures then partially coalesced and the indentations of the C2 region w ere observed. The expanded nuclear envelope at the caudal extremity pe rsisted in caput epididymal spermatozoa. Spherical inclusions within i t did not bind to DNase-gold conjugates but stained for lysine-rich pr oteins. As the sperm traveled down the epididymis, these inclusions am assed near the nuclear pores and were then removed from the nucleus. I n addition, the nuclear mantle was found to have disappeared by the ti me the spermatozoa reached the corpus epididymidis. (C) 1996 Wiley-Lis s, Inc.