Cytochemical and ultrastructural studies on the synaptonemal complex of rat spermatocytes

The effects of several dehydration treatments on the synaptonemal complex (SC), histone solubility in 2.0 M NaCl, and histone-DNA interaction in unfixed rat spermatocytes were evaluated. Freeze substitution with ethanol or dehydration with polyethylene glygol resulted in loss of the SC, preservation of histone solubility and DNA-histone salt linkages. Dehydration with ethylene gylcol or hexylene glycol resulted in preservation of SC with a clear delineation of attachment of the chromatin fibrils to the lateral elements, but a loss of histone solubility and histone-DNA linkages. Dehydration to a fifty percent concentration with glycerol with completion of dehydration with ethylene glycol had the same effect but also resulted in an even distribution of chromatin fibrils. Dehydration with glycerol alone resulted in clumping of chromatin and loss of SC structure, histone solubility and histone-DNA linkages. Partial dehydration to a fifty percent concentration with these three solvents followed by freeze substitution with ethanol resulted in the loss of SC structure and histone solubility but the preservation of histone-DNA linkages. It is likely that these nonaqueous solvents affected the histone hydrophobic groups and thereby altered histone conformation and interactions. These alterations, depending on the treatment used, resulted in the loss or preservation of SC, histone solubility and histone-DNA interactions thereby indicating that the hydrophobic interactions of the histones are crucial for the preservation of these feature of meiotic chromosomes. These results also demonstrate that neither does the preservation of the histone-DNA salt linkages suffice for the preservation of the SC nor does their disruption necessarily result in its loss. The lysine-rich histones, particularly that one unique to meiotic cells, may through their interactions play a crucial role in SC structure.