Arrangement of nuclear structures is not transmitted through mitosis but is identical in sister cells.

Although it is well known that chromosomes are non-randomly organized during interphase, it is not completely clear whether higher-order chromatin structure is transmitted from mother to daughter cells. Therefore, we addressed the question of how chromatin is rearranged during interphase and whether heterochromatin pattern is transmitted after mitosis. We additionally tested the similarity of chromatin arrangement in sister interphase nuclei. We noticed a very active cell rotation during interphase, especially when histone hyperacetylation was induced or transcription was inhibited. This natural phenomenon can influence the analysis of nuclear arrangement. Using photoconversion of Dendra2-tagged core histone H4 we showed that the distribution of chromatin in daughter interphase nuclei differed from that in mother cells. Similarly, the nuclear distribution of heterochromatin protein 1ß (HP1ß) was not completely identical in mother and daughter cells. However, identity between mother and daughter cells was in many cases evidenced by nucleolar composition. Moreover, morphology of nucleoli, HP1ß protein, Cajal bodies, chromosome territories, and gene transcripts were identical in sister cell nuclei. We conclude that the arrangement of interphase chromatin is not transmitted through mitosis, but the nuclear pattern is identical in naturally synchronized sister cells. It is also necessary to take into account the possibility that cell rotation and the degree of chromatin condensation during functionally specific cell cycle phases might influence our view of nuclear architecture.

Distribution function approach to the study of the kinetics of IgM antibody binding to FcγRIIIb (CD16b) receptors on neutrophils by flow cytometry.

Though flow cytometry provides the entire distribution of cellular fluorescence (i.e., "fluorescence profile"), only mean fluorescence data are usually considered in studies of ligand-receptor binding. In this study, we presented a method of the treatment of the temporal evolution of the whole fluorescence profile with a comprehensive statistical approach extended to the reversible binding case. The method was demonstrated in the study of the 1D3 IgM monoclonal antibodies binding to FcγRIIIb receptors (CD16b) on neutrophils. Kinetic experiments were carried out using a FACSCalibur (Becton Dickinson, USA) flow cytometer. For each of four donors, we obtained the distribution of the number of FcγRIIIb surface receptors for neutrophils and the rate constants per receptor: the association rate constant of (2.7±0.4)×10(7) M(-1) min(-1), and the dissociation rate constant of (1.3±0.4)×10(-1) min(-1). Based on the obtained values, the size of the receptor reaction site was estimated at approximately 1 nm. It was found, that cell receptors distributions differed sufficiently between donors in mean and the skewness values, whereas the coefficient of variation (i.e., the ratio of the standard deviation to the mean) did not vary significantly.

Light scattering by neutrophils: model, simulation, and experiment.

We studied the elastic light-scattering properties of human blood neutrophils, both experimentally and theoretically. The experimental study was performed with a scanning flow cytometer measuring the light-scattering patterns (LSPs) of individual cells over an angular range of 5-60 deg. We determined the absolute differential light-scattering cross sections of neutrophils. We also proposed an optical model for a neutrophil as a sphere filled by small spheres and prolate spheroids that correspond to granules and segmented nucleus, respectively. This model was used in simulations of LSPs using the discrete dipole approximation and different compositions of internal organelles. A comparison of experimentally measured and simulated LSPs gives a good qualitative agreement in LSP shape and quantitative agreement in overall magnitude of the differential light-scattering cross section.