Photometric estimations of deoxyribonucleic acid in individual cell nuclei

Abstract

1. 1. The deoxyribonucleic acid content of individual cell nuclei has been measured by microspectrophotometry of nuclei isolated from rat liver and kidney, and of nuclei in chick heart fibroblast cultures and chick embryo liver smears. Measurements have been made on nuclei stained by the Feulgen and methyl green methods, and on unstained nuclei by ultraviolet-absorption methods, with and without ribonuclease pretreatment. 2. 2. The method does not permit of absolute measurements of the DNA content of single nuclei, but side-by-side measurements on large numbers of nuclei from two tissues allow their nuclear populations to be compared. 3. 3. Ribonuclease digestion removes substantial amounts of ultraviolet absorbing material from rat liver and kidney nuclei. Following ribonuclease treatment, ultraviolet measurements present a general picture corresponding to that found by measurement of Feulgen- and methyl green-stained material. 4. 4. Adult rat kidney nuclei form an approximately homogeneous population as regards DNA content, while liver nuclei from the same animal form two main classes, one with the same DNA content as kidney nuclei, and one with approximately twice that amount of DNA. A few nuclei have still higher values. 5. 5. The majority of the nuclei present in chick heart fibroblast cultures have DNA values of the same order as those found in chick embryo liver. In each case, nuclei are found whose DNA content approaches twice that of the majority of the nuclei present. 1 1 Dr.I. Leslie of this Department has recently shown by chemical analysis that the mean DNA content of nuclei isolated in bulk from chick heart fibroblast cultures is of the same order as that of similarly isolated nuclei from embryonic chick heart and liver.