Separation of isolated cell nuclei of tissues of the meal moth, Ephestia kuehniella Z. by metrizamide density gradient centrifugation.

The behaviour of isolated cell nuclei of different tissues in the mediterranean meal moth has been studied in metrizamide density gradients to find whether differences exist in the bouyant density between nuclei derived from different specialized tissues. The different nuclei studied have buoyant densities ranging form 1.228-1.295 g/cm3 in metrizamide density gradients and clear differences exist between different populations of nuclei. The different buoyant densities make it possible to separate isolated nuclei from a heterogeneous population of nuclei according to their characteristic densities. This has been tested by the separation of silk gland nuclei from follicle cell nuclei by the density centrifugation method. The degree of polyploidy of the nuclei is not correlated to a decrease or increase of the buoyant density, which suggests that different amounts of nuclear proteins, ribonucleoproteins or RNA are responsible for the differences determined. These tissue-specific differences of the nuclear densities might be correlated to different transcriptional activities. In addition to this, the isopycnic sedimentation technique in metrizamide density gradient provides a method to purify nuclei very carefully without any visible alteration of their morphology and integrity.