A Method for the Quantitative Evaluation of Eu- and Heterochromatin in Interphase Nuclei using Cytophotometry and Pattern Analysis

The method described herein for the quantitative evaluation of the amount of eu- and heterochromatin in a single interphase cell nucleus is based upon the measurement of optical density in Feulgen-stained nuclei with a scanning cytophotometer (UMSP I). The digitalized values for each grid point are entered via punched paper tape into a computer and processed therein. The position and optical density level of the grid points serve as criteria for the recognition of heterochromatin. The computer calculates the total DNA content of all such points, as well as the proportion of this heterochromatin DNA with respect to the entire DNA content of the cell nucleus. The heterochromatin contents so obtained agree with values obtained from a densitometric determination from photographs of cell nuclei. Agreement with cytogenetic experiments is also observed. The applicability of the method is demonstrated for the heterochromatin content of a variety of rodent species.