A method for preparing highly pure cell nuclei from adult rat brain, using both differential and isopycnic centrifugation in sucrosc media, is described. The morphology of these preparations was examined by both phase contrast and electron microscopy. The isolated nuclei retained many aspects of their in situ morphology; in particular, the nuclear envelope was double layered and interrupted by pore-like discontinuities, and the nuclcoli consisted of irregular masses of densely packed granules. Analyses of these nuclear preparations for cytochromc oxidase and cholincsterasc activity, as well as RNA/DNA ratio, indicated minimal contamination with mitochondria and microsomcs. Problems involving the homogenization technique, choice of ionic conditions in thc homogenization medium, and choice of optimal density of the sucrose solution used for the final purification of nuclei are discussed. Resuhs of application of the technique to isolation of adult rat liver nuclei are also reported.
PLATES 58 TO 62(Received for publication, January 16, 1959) ABSTRACT Comparative electron microscope investigations on sections of the lens cortex of the normal, mature rat, rabbit, monkey, and the normal calf reveal similar patterns of intracellular organization.The superficial lens fiber contains a nucleus, mitochondria, endoplasmic reticulum, dense granules, Golgi complex, and a quantity of small structures of low opacity which appear as filamentous and spherical configurations.Variations in number, distribution, and spatial arrangement of cytoplasmic elements in lens fibers are described. These changes in the pattern of cytoplasmic organization are concomitant with development of fibers and their displacement towards the center of the lens. Structural details of the various zones of the lens epithelium and the lens fibers are compared.
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