Histone redistribution and conformational effect on chromatin induced by formaldehyde

Histone redistributions between endogenous DNA in calf thymus chromatin and exogenous DNA from Clostridium perfringens (69% A + T) or from Micrococcus luteus (30% A + T) induced by 0.6 M NaCl or by 2% formaldehyde were studied by thermal denaturation. The observed redistribution occurred on histone Hl when the exogenous DNA was (A + T)-richer than the DNA in chromatin, and when the mixture was exposed to 0.6 M NaCl or formaldehyde. When a (G + C)-richer DNA was added as the acceptor for histones, no substantial transfer of histones from chromatin DNA to exogenous DNA was found. Thus the activation energy of histone dissociation from chromatin DNA seems to be substantially lowered by 0.6 M NaCl or formaldehyde such that histones (mostly histone Hl) can be dissociated and bind the (A + T)-richer DNA and form a more stable complex. It is suggested that the formaldehyde effect on histones may be due to the loss of positive charges on lysine and arginin residues (probably more on lysine than on arginine) in histones after their rapid reaction with formaldehyde. Formaldehyde treatment of chromatin also distorts the DNA conformation, as revealed by circular dichroism (CD) studies. This structural effect occurs mainly on those base pairs bound by histones other than Hl, or within the chromatin subunit. Histone redistribution is treated as a thermodynamic phenomenon of histone binding to DNA. The validity of using formaldehyde to study chromatin structure is discussed.     

Diffuse and compact chromatin in the cell nuclei from tissues derived from different germ layers

Chromatin structure of nuclei of histogenetically distinct cells of humans and animals under normal and pathological courses of gestation was studied by the method of optic-structural computer analysis. A constant ratio of compact and diffuse chromatin is detected in nuclei of cells originating from all the germ layers. This ratio can change to a variable degree in cases of pathological gestation.     

Histone modification governs the cell cycle regulation of a replication-independent chromatin assembly pathway in Saccharomyces cerevisiae

We describe a replication-independent, cell cycle-regulated chromatin assembly pathway in budding yeast. The activity of this pathway is low in S phase extracts but is very high in G2, M, and G1 cell extracts, with peak activity in late M/early G1. The cell cycle regulation of this pathway requires a specific pattern of posttranslational modification of histones H3 and/or H4, which is distinct for H3/H4 present in S phase versus M and G1 phase cell extracts. Histone H3/H4 modification is therefore important for the reciprocal control of replication-dependent and -independent chromatin assembly pathways during the cell cycle.     

Histone deacetylase. A key enzyme for the binding of regulatory proteins to chromatin

Stone and urine composition were analysed in 75 men and 40 women with recurrent calcium oxalate stone disease (group R) and in 48 men and 19 women who had formed only one calcium-oxalate-containing stone (group S). Patients who had developed stones with a large fraction of calcium phosphate were significantly more frequent in group R than in group S. There was furthermore a higher excretion of calcium and higher calcium oxalate supersaturation levels in patients with stones containing more than 25% calcium phosphate. It was concluded from these observations that the calcium phosphate content of renal stones might be a useful factor in predicting the future course of the disease.     

Flow cytometric and microscopic evaluation and effect on fertility of abnormal chromatin condensation in bovine sperm nuclei

The techniques of Feulgen staining, acridine orange staining, and a sperm chromatin structure assay using acridine orange and flow cytometry were compared for selective examination of bovine sperm nuclei. Twenty frozen semen samples were simultaneously analysed by all three methods. The prevalence of abnormally condensed DNA and its relationship to other semen traits were determined in ejaculates from 70 bulbs presented for routine examination for breeding soundness and in frozen semen from 348 bulls evaluated over five years. A breeding trial with 118 beef heifers using semen from six bulls with different degrees of nuclear abnormalities was performed to assess the importance of the defects with respect to fertility. The results indicate that few spermatozoa with abnormal DNA condensation are found in normal semen, but the incidence increases with disturbance of spermatogenesis. However, high numbers of abnormally condensed nuclei were found in the absence of an increase in other defects. This nuclear defect might be at least partially of epididymal origin; it can lower fertility and can be compensated for by increasing the numbers of normal spermatozoa in the insemination dose. The percentage of abnormally condensed sperm nuclei as detected by Feulgen staining was significantly correlated with that detected by microscopy after acridine orange staining and by the sperm chromatin structure assay. We therefore consider the Feulgen technique to be a valuable tool for assessing the nuclear integrity of bovine spermatozoa.     

Nilsson mean-field plus the extended pairing model description of rare earth nuclei

The Nilsson mean-field plus the extended pairing model for well-deformed nuclei is applied to some representative rare earth examples. The binding energies, some low-lying pair-excited states and evenodd mass differences of Er, Yb and Hf isotopes are calc     

The chromatin structure of well-spread demembranated human sperm nuclei revealed by atomic force microscopy

The fundamental structure formed when genomic DNA is packaged by protamine in the human sperm nucleus still remains essentially unresolved. It is known that the binding of protamine, a small arginine-rich protein, to DNA generates a large dense, hydrophobic complex making the sperm chromatin structure difficult to study microscopically. To visualize the internal nuclear structures, isolated human sperm nuclei were swollen extensively in saline buffer using only a reducing agent. The nuclei were swollen during deposition onto coverglass and then imaged in the atomic force microscope (AFM). The two main results obtained from imaging individual well-spread nuclei indicate that native human sperm chromatin is: (1) particulate, consisting primarily of large nodular structures averaging 98 nm in diameter, and (2) also composed of smaller, nucleosome-like particles observed to form linear chains near the nuclear periphery. These two types of chromatin particles imaged by AFM are remarkably similar to other AFM measurements made on native and reconstituted sperm and somatic chromatin.     

Attractor dynamics and semantic neighborhood density: Processing is slowed by near neighbors and speeded by distant neighbors.

The authors investigated semantic neighborhood density effects on visual word processing to examine the dynamics of activation and competition among semantic representations. Experiment 1 validated feature-based semantic representations as a basis for computing semantic neighborhood density and suggested that near and distant neighbors have opposite effects on word processing. Experiment 2 confirmed these results: Word processing was slower for dense near neighborhoods and faster for dense distant neighborhoods. Analysis of a computational model showed that attractor dynamics can produce this pattern of neighborhood effects. The authors argue for reconsideration of traditional models of neighborhood effects in terms of attractor dynamics, which allow both inhibitory and facilitative effects to emerge. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ultrastructure of chromatin in nuclei of hepatocytes of regenerating guinea pig liver after administration of vitamin B12

Experiments have been carried out on 10 male guinea-pigs (0.5 kg, 6 month old). The experimental animals have been submitted to partial hepatectomy of the left lobe of the liver (lobus externus sinister) with and without the administration of vitamin B (0.8 mgr/kg). 10 nuclei of hepatocytes have been expressed in conventional units.     

Histone H1 reduces the frequency of initiation in Xenopus egg extract by limiting the assembly of prereplication complexes on sperm chromatin

Somatic histone H1 reduces both the rate and extent of DNA replication in Xenopus egg extract. We show here that H1 inhibits replication directly by reducing the number of replication forks, but not the rate of fork progression, in Xenopus sperm nuclei. Density substitution experiments demonstrate that those forks that are active in H1 nuclei elongate to form large tracts of fully replicated DNA, indicating that inhibition is due to a reduction in the frequency of initiation and not the rate or extent of elongation. The observation that H1 dramatically reduces the number of replication foci in sperm nuclei supports this view. The establishment of replication competent DNA in egg extract requires the assembly of prereplication complexes (pre-RCs) on sperm chromatin. H1 reduces binding of the pre-RC proteins, XOrc2, XCdc6, and XMcm3, to chromatin. Replication competence can be restored in these nuclei, however, only under conditions that promote the loss of H1 from chromatin and licensing of the DNA. Thus, H1 inhibits replication in egg extract by preventing the assembly of pre-RCs on sperm chromatin, thereby reducing the frequency of initiation. These data raise the interesting possibility that H1 plays a role in regulating replication origin use during Xenopus development.     

Histone deacetylase and retinoblastoma protein

The balance between cellular proliferation and differentiation is strictly controlled in the cell and the deregulation of this balance can lead to tumour formation. The tumour suppressor protein Rb plays a key role in this balance essentially by repressing progression through the cell cycle and thereby it blocks the cell in G1 phase. Rb represses S phase genes through the recruitment of an enzyme which modifies DNA structure, the histone deacetylase HDAC1. The Rb/HDAC1 complex is a key element in the control of cell proliferation and differentiation. Moreover, this complex is likely to be a target for transforming viral proteins.     

Histone synthesis in Trypanosoma cruzi

Trypanosoma cruzi is an ancient, parasitic eukaryote which does not undergo chromatin condensation during cell division. This behavior may be explained if one considers the strong amino acid sequence divergence of Trypanosoma histones compared to higher eukaryotes. In the latter organisms histone synthesis is coupled to DNA replication. Considering the nonconserved amino acid sequence of T. cruzi histones, as well as the absence of chromatin condensation in this organism, we have studied histone synthesis in relation to DNA replication in this parasite. We have found that core histones and a fraction of histone H1 are synthesized concomitantly to DNA replication. However, another fraction of histone H1 is constitutively synthesized.     

Load distribution in osseointegrated implant supporting extended and non extended dentures

There is a controversy among prosthodontists concerning the most favourable superstructure design of a prosthesis supported by implants. Some investigators used the fully extended denture, others used a non extended. This study evaluated the load distribution pattern occurring in implants with the two designs. A real clinical situation which includes 4 osseointegrated implants that are connected to each other with a superstructure bar and support an acrylic dentures was transferred into a 3-D geometric model. With the 3-D FEM it was possible to compare between the two types of acrylic dentures.     

Histone stoichiometry and DNA circularization in archaeal nucleosomes

Recombinant (r)HMfB (archaealhistone B fromMethanothermusfervidus) formed complexes with increasing stability with DNA molecules increasing in length from 52 to 100 bp, but not with a 39 bp molecule. By using125I-labeled rHMfB-YY (an rHMfB variant with I31Y and M35Y replacements) and32P-labeled 100 bp DNA, these complexes, designated archaeal nucleosomes, have been shown to contain an archaeal histone tetramer. Consistent with DNA bending and wrapping, addition of DNA ligase to archaeal nucleosomes assembled with 88 and 128 bp DNAs resulted in covalently-closed monomeric circular DNAs which, following histone removal, were positively supercoiled based on their electrophoretic mobilities in the presence of ethidium bromide before and after relaxation by calf thymus topoisomerase I. Ligase addition to mixtures of rHMfB with 53 or 30 bp DNA molecules also resulted in circular DNAs but these were circular dimers and trimers. These short DNA molecules apparently had to be ligated into longer linear multimers for assembly into archaeal nucleosomes and ligation into circles. rHMfB assembled into archaeal nucleosomes at lower histone to DNA ratios with the supercoiled, circular ligation product than with the original 88 bp linear version of this molecule. Archaeal histones are most similar to the globular histone fold region of eukaryal histone H4, and the results reported are consistent with archaeal nucleosomes resembling the structure formed by eukaryal histone (H3+H4)2tetramers.