Nuclear matrix of the lower eukaryote Physarum polycephalum and the mammalian epithelial LLC-PK1 cell line. A comprehensive investigation of different preparation procedures

DNA flow cytometry of human spermatozoa: consistent stoichiometric staining of sperm DNA using a novel decondensation protocol

Rapid flow cytometric measurement of the frequency of aneuploid human sperms is in increasing demand but development of an exploitable method is hindered by difficulties of stoichiometric staining of sperm DNA. An aggressive decondensation protocol is needed after which cell integrity still remains intact. We used flow cytometry to examine the effect of lithium diiodosalicylate (LIS, chaotropic agent) on fluorescence intensity of propidium iodide-treated human spermatozoa from 10 normozoospermic men. When flow cytometric identification of diploid spermatozoa was achieved, validation was performed after sorting by three-color FISH. In contrast with the extremely variable histograms of nondecondensed sperms, consistent identification of haploid and diploid spermatozoa was possible if samples were decondensed with LIS prior to flow cytometry. A 76-fold enrichment of diploid sperms was observed in the sorted fractions by FISH. A significant correlation was found between the proportion of sorted cells and of diploid sperms by FISH. Application of LIS during the preparation of sperm for flow cytometry appears to ensure the stoichiometric staining of sperm DNA, making quantification of aneuploid sperm percentage possible. To our knowledge this is the first report in terms of separating spermatozoa with confirmedly abnormal chromosomal content. High correlation between the proportion of cells identified as having double DNA content by flow cytometry and diploid sperm by FISH allows rapid calculation of diploidy rate.

Tropomyosin is localized in the nuclear matrix and chromosome scaffold of Physarum polycephalum

The nuclei and chromosomes were isolated from plasmodia of Physarum polycephalum. The nuclear matrix and chromosome scaffold were obtained after the DNA and most of the proteins were extracted with DNase I and 2 M NaCl. SDS-PAGE analyses revealed that the nuclear matrix and chromosome scaffold contained a 37 kD polypeptide which is equivalent to tropomyosin in molecular weight. Immunofluorescence observations upon slide preparations labeled with anti-tropomyosin antibody showed that the nuclear matrix and chromosome scaffold emanated bright fluorescence, suggesting the presence of the antigen in them. Immunodotting results confirmed the presence of tropomyosin in the nuclear matrix and chromosome scaffold. Immunoelectron microscopic observations further demonstrated that tropomyosin was dispersively distributed in the interphase nuclei and metaphase chromosomes.

Cloning and characterization of Physarum polycephalum tectonins. Homologues of Limulus lectin L-6

Previous investigators have reported the presence of two dominant proteins, tectonin I (25 kDa) and tectonin II (39 kDa), in nuclei and nuclear matrix from plasmodia of Physarum polycephalum. We demonstrate, by a modification of the nuclear isolation protocol and by protease sensitivity, that the tectonins are not nuclear proteins but rather are located on the exterior surface of the plasma membrane. We report the sequences of cDNAs of tectonins I and II, which encode 217 and 353 amino acids, respectively. Tectonin I is homologous to the C-terminal two-thirds of tectonin II. Both proteins contain six tandem repeats that are each 33-37 amino acids in length and define a new consensus sequence. Homologous repeats are found in L-6, a bacterial lipopolysaccharide-binding lectin from horseshoe crab hemocytes. The repetitive sequences of the tectonins and L-6 are reminiscent of the WD repeats of the beta-subunit of G proteins, suggesting that they form beta-propeller domains. Tectonin II has an additional N-terminal domain that includes a 47-residue sequence highly similar to the galactoside-binding sequence of the B-chain of ricin. The tectonins may be lectins that function as part of a transmembrane signaling complex during phagocytosis.

Different concentrations of Mg++ ions affect nuclear matrix protein distribution during thermal stabilization of isolated nuclei

The nuclear matrix, a proteinaceous network believed to be a scaffolding structure determining higher-order organization of chromatin, is usually prepared from intact nuclei by a series of extraction steps. In most cell types investigated the nuclear matrix does not spontaneously resist these treatments but must be stabilized before the application of extracting agents. Incubation of isolated nuclei at 37C or 42C in buffers containing Mg++ has been widely employed as stabilizing agent. We have previously demonstrated that heat treatment induces changes in the distribution of three nuclear scaffold proteins in nuclei prepared in the absence of Mg++ ions. We studied whether different concentrations of Mg++ (2.0-5 mM) affect the spatial distribution of nuclear matrix proteins in nuclei isolated from K562 erythroleukemia cells and stabilized by heat at either 37C or 42C. Five proteins were studied, two of which were RNA metabolism-related proteins (a 105-kD component of splicing complexes and an RNP component), one a 126-kD constituent of a class of nuclear bodies, and two were components of the inner matrix network. The localization of proteins was determined by immunofluorescent staining and confocal scanning laser microscope. Mg++ induced significant changes of antigen distribution even at the lowest concentration employed, and these modifications were enhanced in parallel with increase in the concentration of the divalent cation. The different sensitivity to heat stabilization and Mg++ of these nuclear proteins might reflect a different degree of association with the nuclear scaffold and can be closely related to their functional or structural role.

Induction of dedifferentiated clones of LLC-PK1 cells upon long-term exposure to dichlorovinylcysteine

Dichlorovinylcysteine (DCVC), the key metabolite of the nephrotoxic and nephrocarcinogenic chemicals, trichloroethylene and dichloroacetylene, exerts potent acute cellular toxicity in LLC-PK1 cells (Vamvakas S., Bittner, D., Dekant, W. and Anders, M.W. (1992). Events that precede and that follow S-(1,2-dichlorovinyl)-L-cysteine-induced release of mitochondrial Ca2+ and their association with cytotoxicity to renal cells. Biochem. Pharmacol. 44, 1131-1138). In the present study we investigated whether long-term exposure of LLC-PK1 cells to low, non-cytotoxic concentrations of DCVC results in stable morphological and biochemical dedifferentiation. After 7 weeks exposure to 1 and 5 microM DCVC, morphologically changed single cells were picked under the microscope and cultured in absence of DCVC for 4-8 weeks. In contrast to the physiological cuboidal shape of untreated LLC-PK1 cells, the clones derived from long-term exposure to DCVC consisted of elongated, spindle-shaped cells tending to form irregular borders. Moreover, glucose uptake, pH-dependent ammonia production and dome formation, important indicators of the renal tubule origin of the LLC-PK1 cells, were severely impaired in the clones. In addition to the loss of membrane polarity, the clones exhibited altered composition of the nuclear matrix and intermediate filament proteins by two-dimensional gel electrophoresis, increased poly(ADP-ribosyl)ation of nuclear proteins and enhanced expression of c-fos. The induction of dedifferentiated LLC-PK1 clones with stable characteristics upon long-term exposure to the nephrocarcinogen DCVC may represent a useful in vitro model to study biochemical alterations involved in chronic renal toxicity and carcinogenicity.

Nuclear matrix and the cell cycle

The facts that the nuclear matrix represents a structural framework of the cell nucleus and that nuclear events, such as DNA replication, transcription, and DNA repair, are associated with this skeletal structure suggest that its components are subject to cell cycle-regulatory mechanisms. Cell cycle regulation has been shown for nuclear lamina assembly and disassembly during mitosis and chromatin reorganization. Little attention has so far been paid to internal nuclear matrix proteins and matrix-associated proteins with respect to the cell cycle. This survey attempts to summarize available data and presents experimental evidence that important metabolic functions of the nucleus are regulated by the transient, cell cycle-dependent attachment of enzymes and regulatory proteins to the nuclear matrix. Results on thymidine kinase and RNA polymerase during the synchronous cell cycle of Physarum polycephalum demonstrate that reversible binding to the nuclear matrix represents an additional level of regulation for nuclear processes.

Chromatin domains and prediction of MAR sequences

Polynuceosomes are constrained into loops or domains and are insulated from the effects of chromatin structure and torsional strain from flanking domains by the cross-complexation of matrix-attached regions (MARs) and matrix proteins. MARs or SARs have an average size of 500 bp, are spaced about every 30 kb, and are control elements maintaining independent realms of gene activity. A fraction of MARs may cohabit with core origin replication (ORIs) and another fraction might cohabit with transcriptional enhancers. DNA replication, transcription, repair, splicing, and recombination seem to take place on the nuclear matrix. Classical AT-rich MARs have been proposed to anchor the core enhancers and core origins complexed with low abundancy transcription factors to the nuclear matrix via the cooperative binding to MARs of abundant classical matrix proteins (topoisomerase II, histone H1, lamins, SP120, ARBP, SATB1); this creates a unique nuclear microenvironment rich in regulatory proteins able to sustain transcription, replication, repair, and recombination. Theoretical searches and experimental data strongly support a model of activation of MARs and ORIs by transcription factors. A set of 21 characteristics are deduced or proposed for MAR/ORI sequences including their enrichment in inverted repeats, AT tracts, DNA unwinding elements, replication initiator protein sites, homooligonucleotide repeats (i.e., AAA, TTT, CCC), curved DNA, DNase I-hypersensitive sites, nucleosome-free stretches, polypurine stretches, and motifs with a potential for left-handed and triplex structures. We are establishing Banks of ORI and MAR sequences and have undertaken a large project of sequencing a large number of MARs in an effort to determine classes of DNA sequences in these regulatory elements and to understand their role at the origins of replication and transcriptional enhancers.