Mass and molecular weight of isolated nuclear rings

Nuclear rings are cell structures found at the nuclear cortex wedged between the nuclear envelope and the chromatin fiber network. In previous publications we have dealt with their morphology, relationships with the nuclear membranes, chromatin fibers and cytoskeletal filaments; and more recently, with their measurements at high electron microscope resolution. In this article we have calculated the mass and molecular weight of 336 isolated nuclear rings from human circulating lymphocytes using a photometric procedure and polystyrene latex spheres as the standard for weight calibration. Our results show a range of mass of 0.4-35.5 x 10(-16) g (equivalent to 0.2-21.2 x 10(8) Da with a positively skewed distribution (median: 3.3 x 10(-16) g or 2.0 x 10(8) Da). Mass and volume of nuclear rings were highly correlated. In addition, it was possible to calculate the area, the whole mass and the mass per unit area of the nuclear envelope present in the center of the nuclear rings. The mass of this area also shows a lognormal distribution (median of mass/unit area: 37.3 x 10(-8) pg/nm2 or 1.9 x 10(5) Da/nm2). We discuss the significance of this results as parameters for the characterization of the nuclear rings and their possible implications for a new interpretation of nuclear cortex architecture, nucleocytoplasmic traffic and macromolecule segregation between the two main cell compartments.