Extent of sperm chromatin hydration determined by atomic force microscopy.

Volume measurements were performed on intact bull and mouse sperm heads and amembranous sperm nuclei, both in the fully hydrated (fluid cell) and dehydrated (air-dried on glass coverslips) states by atomic force microscopy (AFM). Data were obtained by analyzing a small population of cells/nuclei, as well as by performing repeated measurements on single cells imaged following the addition of increasing concentrations of propanol. Results show that the volume of fully hydrated, intact sperm heads and amembranous sperm chromatin particles are at least twice the volume of their air-dried counterparts. Dehydration occurs rapidly in air, and the reduction in volume of chromatin induced by water loss appears to be completely reversible. These studies demonstrate that both mouse and bull sperm chromatin are extensively hydrated in the native state, and are not as compact as previous studies have suggested.