A cytochemical study of the nucleolus and nucleolus-related structures during human spermatogenesis.

Besides the components of typical nucleoli, three other nuclear structures were identified in spermatogonia by positive silver staining: dense centers, fibrillar regions, and dense granules. There was a close relationship between the dense centers and fibrillar regions in spermatogonia and spermatocytes, whereas the dense granules, which appeared dispersed throughout the nucleoplasm of spermatogonia, became localized at the periphery of chromosomes in spermatocytes. From the beginning of spermiogenesis, these three structures then appeared in direct relationship with the dense fibrillar component of the nucleolus. At the Golgi phase, a new nuclear structure also appeared in close relationship with the dense fibrillar component. As it was morphologically similar to the fibrillar region, but not silver stained, it was designated fibrillar structure. With further spermatid development, as the dense fibrillar component gradually disappeared, a sharp increase in the number of the associated dense granules was observed; these granules then disappeared as well. In spermatids at cap phase, each fibrillar region appeared intimately associated with several fibrillar structures. In maturing spermatids, silver staining became confined to the fibrils that appeared located inside the nuclear vacuole. The nuclear vacuole also contained a dense fibrillar structure in intimate relationship with these fibrils and the peripheral condensed chromatin. Ethidium bromide-PTA, Na-tungstate and EDTA regressive staining suggest the presence of RNP in the fibrillar regions, dense granules and intravacuolar fibrils, and the presence of DNP in the fibrillar structures.