A cytochemical study of pycnotic nuclear degeneration

Abstract

Pycnotic degeneration of neoplastic and normal nuclei of mice has been studied cytologically and cytochemically, in pieces of tissues removed some time after subcutaneous transplantation. The cytological changes in pycnosis were found to be about as they have often been described earlier: the nuclei become spherical, shrink progressively, the nucleoli become lost, the chromatin becomes homogeneous. The relative changes in total desoxyribose nucleic acid were followed by the Feulgen reaction; the methylgreen stain was used as an index of nuclei acid polymerization; the Millon reaction was used for the detection of the protein changes. In order to measure the amounts of the Feulgen and methylgreen dye, respectively the color developed by the Millon reaction within individual nuclei, the photometric microscopic method after Pollister and Ris was used, which allows the estimation of relative amounts of colored precipitates within individual nuclei of fixed and stained sections.

Using these methods the nucleoprotein composition of resting nuclei of a viable tumortissue was compared with that of three pycnotic stages (Stage I, II, III) in nuclei of necrotic areas of the same tumor tissue (Sarcoma 180). In Sarcoma 180 the change from a fresh tumor cell to Pycnosis I involves loss of nearly half the protein, no significant decrease in desoxyribose nucleic acid, and depolymerisation of over half of the desoxyribose nucleic acid. Later these processes continue, and there is added progressive loss of DNA. It is pointed out that at any pycnotic stage there is a total protein equivalent to about 20 times the highly polymerised (methylgreen positive) DNA, which is the ratio found in non-pycnotic nuclei of the type from which these were derived. It is suggested that this part of the pycnotic chromatin represents the unaltered nucleoprotein.

In transplanted liver nuclei pycnosis is much more rapid than in neoplastic tissue, but otherwise the two processes are similar both cytologically and chemically.

The discussion points out that: a) there is no real increase in chromatin stainability in pycnotic nuclei; b) the change of shape in pycnosis may be due to lower nuclear viscosity accompanying the DNA depolymerisation; c) the highly polymerised state of the DNA may depend upon the presence of some particular protein, possibly histone; and d) that pyenosis can be interpreted as showing high proteolytic activity in the nucleus and a delayed nuclease activity.