MORPHOLOGY AND BEHAVIOR OF SILVER-STAINED CHROMATID CORES IN MITOTIC CHROMOSOMES ANALYZED BY WHOLE-MOUNT ELECTRON-MICROSCOPY

Using silver staining and the whole mount electron microscopy techniqu e of squashed chromosomes, we studied the substructural organization a nd behaviour of chromatid cores in mitotic chromosomes of spermatogoni a of the grasshopper Oedaleus infernalis during mitosis. It was found that the formation of mitotic chromatid cores takes place during the t ransition from prophase to prometaphase. Each chromosome contains two compact chromatid cores which are surrounded by a halo of dispersed ar gyrophilic material emanating radially from the cores. In early metaph ase the chromatid core usually appears as an extended, slender network running longitudinally through the entire length of the chromatid, wh ile in late metaphase the core frequently has a spiral appearance. In addition, our results revealed the existence of interconnections betwe en sister chromatid cores along their entire length, as a result of wh ich sister chromatid cores appear as a single interconnected core netw ork in mitotic metaphase chromosomes. At this stage the core occupies a lateral position in each chromatid. However, during the transition f rom metaphase to anaphase, the interconnections are gradually released to allow the individualization of sister chromatid cores and the segr egation of chromosomes. The core comes to occupy a central position in each segregated chromatid. These findings demonstrate the presence of an intrinsic interconnected core network within metaphase chromosomes which could be involved in the maintenance and segregation of chromos omes during mitosis.