Structural transitions of chromatin in isolated Xenopus erythrocyte nuclei. II. Computer-based image analysis

The morphology of isolated Xenopus erythrocyte nuclei is largely determined by the ionic constitution of the isolation medium. Electron microscopy of thin sections of nuclei isolated under varying ionic conditions has revealed four different morphological types with characteristic chromatin configurations. These nuclei have been used to study the condensation of chromatin within the confines of the nucleus. Electron micrographs of thin nuclear sections have been analysed by computer on the basis of their intensity of staining with lead citrate/uranyl acetate. The staining pattern (image analysis scan) is characteristic for each nuclear morphology and can be explained by a model which assumes that there are only four higher-order conformations that chromatin can adopt within the nucleus. These are present in varying amounts in the different nuclear types and an attempt has been made to equate the peaks identified by image analysis with previously-described chromatin structures. The results of this study serve to emphasize the potential of computer-based image analysis in the study of chromatin structure.