Evidence of repetitive patterns of chromatin distribution in cell nuclei of rat liver

Samples of rat livers were fixed in glutaraldehyde, contrasted en bloc with phosphotungstic acid, embedded in an epoxy resin and serially sectioned. The study of three-dimensional models of 20 complete nuclei shows that all of them share some general features: they have more than one nucleolus (2-4), an irregular layer of compact chromatin adjacent to the nuclear membrane and well-delimited clumps of chromatin both in the nuclear sap and surrounding the nucleoli. A space of 8 sections containing the central nucleolus and a lateral one was studied in detail. In this space, 8 clumps of compact chromatin were found in 17 nuclei and 9 clumps in the other 3 nuclei. No other number of clumps was found in those zones. In all the nuclei studied the compact chromatin surrounding the central nucleolus contacts the nuclear envelope. This contact takes place in a region almost diametrically opposed to the lateral nucleolus in 13 nuclei. In 7 nuclei, these structures were at angles between 50 and 125 degrees. These results support the existence of nonrandom repetitive patterns of chromatin distribution in liver cells.