On the origin of nuclear vacuoles in spermatozoa a fine structural and cytochemical study in mice

Morphological and cytochemical changes in nucleoli of spermatids of the mouse during spermiogenesis were examined. Thus, it could be shown that the nucleolar derivatives of the elongation-phase, clusters of coiled fibers that are bordered with spheroidal bodies, show comparable chemical properties as the precursor structure, the fibrillar component, which is known for its transcriptional activity. With progressing development, these nucleolar derivatives continually decrease in size and density, preserving their chemical properties. They persist far beyond into the maturation-phase and will decrease at the time chromatin condensation appears finished. There only remain the spaces in which they formerly existed, now called nuclear vacuoles. A possible function of nuclear vacuoles with respect to chromatin decondensation during the process of fertilization is mentioned.