Microfluorometric investigations of chromatin structure

Summary

Substitution of various metal compounds for aluminum ammonium sulfate in the aluminum-morin procedure developed by Malinin (1978) revealed that only one compound (indium trichloride) yielded fluorescent patterns in mastocytoma cells and isolated nuclei resembling those of the standard procedure. All other compounds tested, including zinc acetate, zinc iodide, zinc sulfate, calcium chloride, beryllium nitrate, and zirconium nitrate, produced either only slight enhancement of fluorescence over that obtained in control material treated with morin alone; or the fluorescence was no greater than that of control material. A microfluorometric comparison of thymocyte and 2c hepatocyte nuclei stained by either the indiumor aluminum-morin procedures revealed that the fluorescence of the more loosely organized chromatin of 2c hepatocyte nuclei was 30–40% greater than that of the more condensed chromatin of thymocyte nuclei. In addition, the fluorescence of indium-pretreated nuclei was either the same or slightly greater than that of aluminum-pretreated nuclei. Extraction with RNase always resulted in a loss of fluorescence in aluminum-pretreated nuclei; however, somewhat different results were obtained in indium-pretreated nuclei: the fluorescence of thymocyte nuclei declined (but not so much as that of nuclei pretreated with aluminum), and hepatocyte nuclei either displayed no change in fluorescence or their fluorescence increased slightly. Since both aluminum- and indium-morin procedures, used with or without RNase extraction, yield consistently disparate values in nuclei displaying differing degrees of chromatin condensation, it seems likely that these procedures might be useful in studies requiring the demonstration of structural differences in chromatin.