UNUSUAL NUCLEAR-STRUCTURE OF THE SPERMATOZOON IN A MARSUPIAL, SMINTHOPSIS-CRASSICAUDATA

The organization of sperm chromatin in the dasyurid marsupial, Smintho psis crassicaudata, was investigated using various morphological techn iques. Transmission electron microscopy indicates two quite distinct c hromatin regions became evident tate in spermiogenesis with an outer g lobular region containing blocks of very electron-dense chromatin. Flu orescent light microscopical studies after staining with DNA dyes and 7-amino actinomycin D of testicular, caput, and cauda epididymal sperm atozoa showed that this region fluoresced less brightly than the rest of the nucleus, indicating the presence of fewer DNA binding sites. Fr eeze fracture showed that the chromatin in most of the nucleus had ran domly arranged particles of various sizes, but that of the outer regio n was composed entirely of small particles. This outer region was more resistant to low concentrations of the ionic detergent, SDS, whereas both guanidine hydrochloride and urea together with sodium chloride ge nerally dispersed all the chromatin except that in the outer globular region and in a localized area of the nucleus beneath the acrosome. Th is study has thus revealed that the outer globular chromatin of these spermatozoa responds differently to ionic detergents and protein denat uring agents and has a different chromatin organization than most of t he rest of the nucleus. The significance of these differences remains, however, to be determined. (C) 1994 Wiley-Liss, Inc.