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B Piña

Publications and source records attributed to B Piña.

30 records · Page 2Linked to original sources
PubMed1990

DNA rotational positioning in a regulatory nucleosome is determined by base sequence. An algorithm to model the preferred superhelix.

MMTV-LTR sequences -190/-45 position a histone octamer both in vivo and in vitro. Experimental evidence suggested that nucleosome rotational positioning is determined by the DNA sequence itself. We developed an algorithm that is able to predict the most favorable path of a given DNA sequence over a histone octamer, based on rotational preferences of different dinucleotides. Our analysis shows that these preferences are sufficient for explaining the observed rotational positioning of the MMTV-LTR nucleosome, at one base pair accuracy level. Computer-generated 3-D models of the experimentally calculated and predicted MMTV-LTR nucleosome show that the predicted orientation is fully compatible with the currently available data in terms of accessibility of relevant sequences to regulatory proteins.

Algorithms↗
PubMed1990

Nucleosome positioning modulates accessibility of regulatory proteins to the mouse mammary tumor virus promoter.

Minichromosomes containing the MMTV hormone responsive element (HRE) exhibit precisely positioned nucleosomes. Chromatin reconstitution of short HRE DNA fragments also results in precise positioning of nucleosomes as revealed by footprinting, which suggests that information for nucleosome phasing is contained within this short sequence. While hormone receptors bind naked DNA and reconstituted nucleosomes with similar affinities (3- to 5-fold difference), NFI, a transcription factor essential for efficient utilization of the MMTV promoter, binds naked DNA very tightly but does not bind the nucleosomally organized promoter. Hormone receptor binding to the MMTV nucleosome does not dissociate the nucleosome but leads to greater accessibility of the promoter-proximal end to exonuclease III. Precise positioning of one nucleosome over the MMTV promoter could repress transcription by preventing NFI binding in the absence of hormone, while still allowing interaction of activated hormone receptor with HRE.

Animals↗
PubMed1990

Hormonal induction of transfected genes depends on DNA topology.

Plasmids containing the hormone regulatory element of mouse mammary tumor virus linked to the thymidine kinase promoter of herpes simplex virus and the reporter gene chloramphenicol acetyltransferase of Escherichia coli respond to glucocorticoids and progestins when transfected into appropriate cells. In the human mammary tumor cell line T47D, the response to progestins, but not to glucocorticoids, is highly dependent on the topology of the transfected DNA. Although negatively supercoiled plasmids respond optimally to the synthetic progestin R5020, their linearized counterparts exhibit markedly reduced progestin inducibility. This is not due to changes in the efficiency of DNA transfection, since the amount of DNA incorporated into the cell nucleus is not significantly dependent on the initial topology of the plasmids. In contrast, cotransfection experiments with glucocorticoid receptor cDNA in the same cell line show no significant influence of DNA topology on induction by dexamethasone. A similar result was obtained with fibroblasts that contain endogenous glucocorticoid receptors. When the distance between receptor-binding sites or between the binding sites and the promoter was increased, the dependence of progestin induction on DNA topology was more pronounced. In contrast to the original plasmid, these constructs also revealed a similar topological dependence for induction by glucocorticoids. The differential influence of DNA topology is not due to differences in the affinity of the two hormone receptors for DNA of various topologies, but probably reflects an influence of DNA topology on the interaction between different DNA-bound receptor molecules and between receptors and other transcription factors.

Animals↗
PubMed1988

Differential acetylation of core histones in rat cerebral cortex neurons during development and aging.

Core histones can be modified by aceylation and this modification has been correlated with the modulation of chromatin condensation and histone deposition. We have now studied the levels of acetylation of the core histones in rat brain cortical neurons from the middle of the period of neuronal proliferation through postnatal development and aging. The results show that the level of acetylation of H4 decreases with age. The kinetics of H4 deacetylation show a perinatal fast phase followed by a much slower phase that spans the rest of the period examined. H4 deacetylation is accounted for by the decrease of the monoacetylated species, the proportions of the more highly acetylated species remaining essentially constant. By contrast to histone H4, the overall levels of acetylation and the proportions of the different acetylated species of H2A, H2B and H3 remain unchanged throughout the period examined. Furthermore, the variants belonging to a given histone class always show the same level of acetylation. The fact that in neurons the level of monoacetylated H4 decreases during development and aging, in sharp contrast with the constancy of the levels of all other acetylated histone species, raises the possibility that in interphase chromatin monoacetylated H4 may have a central role in the modulation of chromatin structure. The results also suggest that the slow decrease of the proportion of monoacetylated H4 may imply a gradual loss of chromatin structural plasticity and thus lead to aging.

Acetylation↗
PubMed1987

Changes in H1 complement in differentiating rat-brain cortical neurons.

Neuronal nuclei have a low H1 content. A stoichiometry of 0.47 molecule/nucleosome, on average, is calculated for rat brain cortical neurons by comparing its H1 content with that of liver nuclei. The H1 fraction of rat cerebral cortex neurons has been resolved into five subtypes, H1a--e, that have the same mobility as the unphosphorylated H1 forms of other rat tissues. The subtypes H1a--d decay exponentially during postnatal development and are substituted to different extents by H1e. The higher replacement rate is shown by H1a with an apparent half-lifetime of about 5 days. The corresponding values for H1b, H1c and H1d are 11, 21 and 15 days. Several conclusions can be drawn from the observation of postnatal changes in H1 subtype proportions. The low H1 content of neuronal nuclei does not imply the presence of notable peculiarities in subtype composition or in subtype substitution pattern. There is turnover of H1 in differentiating neurons once cell proliferation and DNA replication have ceased. The relative rates of synthesis and/or degradation of the subtypes differ in germinal cells and in neurons. Comparison with previous results on H1 degrees accumulation also shows that in cortical neurons the regulation of the subtypes H1a--e differs from that of H1 degrees.

Animals↗
PubMed1987

Changes in the proportions of histone H1 subtypes in brain cortical neurons.

Histone H1(0) is found in tissues with little or no cellular proliferation and has been shown to accumulate during cellular terminal differentiation. Two subtypes of H1(0), H1 a and H1 b, are present in any tissue where the protein has been detected. We report here the first evidence of an age-dependent change in the proportions of H1 subtypes. In rat cerebral cortex neurons the proportion of H1 a rises from 44% of total H1 at birth to about 80% at day 300. These results show that terminally differentiated neurons synthesize and exchange H1 at a significant rate.

Aging↗
PubMed1987

Changes in histones H2A and H3 variant composition in differentiating and mature rat brain cortical neurons.

Rat brain cortical neurons originate from germinal cells during a period of 6 days immediately before birth. Upon leaving the proliferative layer neurons become irreversibly quiescent. We have previously reported the presence of core histone nonallelic variants in terminally differentiated rat brain cortical neurons. Although the functional significance of core histone variants is unknown, several lines of evidence suggest that the processes of variant replacement could be involved in the structural and functional differentiation of chromatin. Here we describe the changes in core histone composition that occur during postnatal development. The changes in chromatin composition are already apparent at birth, suggesting that the change in synthesis patterns is related to the arrest of cell proliferation and neuron commitment. During postnatal development H2A.2, H2A.x, and H3.3 accumulate, whereas H2A.1, H3.1, and H3.2 decrease. H2A.z is the only variant that remains constant. The time courses of replacement and the observed variant proportions when the variant composition approaches the equilibrium suggest that all H2A variants are synthesized either in germinal cells or in neurons, whereas H3.1 and H3.2 seem to be synthesized only in germinal cells. The extent of the replacement of H3.1 and H3.2 by H3.3 shows that the exchange process affects most of the chromatin. The half-life times of H2A.1 and H3.2 were calculated from their respective exponential decays. Values of 65 days or less and 142 days were found for H2A.1 and H3.2, respectively. The preferential replacement of H2A.1 over H3.2 reinforces the view that the histone core does not degrade as a single unit.

Aging↗
PubMed1985

Core histone variants and ubiquitinated histones 2A and 2B of rat cerebral cortex neurons.

The pattern of non-allelic variants of core histones was investigated in terminally differentiated rat cerebral cortex neurons. At 30 days two major H2A variants are present, H2A.1 and .2, together with two minor components, .x and .z. H2B has two variants, H2B.1 and .2, and H3 presents three variants, H3.1, .2 and .3. The ubiquitinated adducts of all H2A and H2B variants can be recognised on two-dimensional electrophoresis as forming a pattern similar to that of the unmodified species. uH2A amounts to 12-14% of total H2A. All H2A variants appear to be equally modified. uH2B amounts to 1-2% of total H2B.

Animals↗
PubMed1985

Fluorescent properties of histone-1-anilinonaphthalene 8-sulfonate complexes in the presence of denaturant agents: application to the rapid staining of histones in urea and Triton-urea-polyacrylamide gels.

In the present report it is shown that histone bands in urea-acetic acid or Triton-urea-acetic acid-polyacrylamide gels can be stained with the fluorescent dye 1-anilinonaphthalene 8-sulfonate and visualized by transillumination of the gel with an uv-light source. The 1-anilinonaphthalene 8-sulfonate staining method described here for urea and Triton-urea gels is rapid (it can be completed in 90 min) and allows the detection of less than 1 micrograms of histone per band.

Anilino Naphthalenesulfonates↗
PubMed1984

Differential kinetics of histone H1(0) accumulation in neuronal and glial cells from rat cerebral cortex during postnatal development.

The accumulation of histone H1(0) as been studied in neuronal and glial nuclei from rat cerebral cortex during postnatal development. In neurons H1 degrees represents approximately 2% of the H1 content at birth and remains unchanged until day 8. Beyond this point H1 accumulates rapidly until day 18, where it levels off at 16% of H1. The midpoint of the transition is at day 14. In glial cells H1 represents approximately 2.5% of the H1 at birth. It starts to accumulate between days 18 and 21; its concentration raises rapidly up to day 30 slowing down from then on. At day 300 (the farthest point examined) it represents 21% of H1. These results are discussed in relation to the events of the postnatal development of the cerebral cortex in the rat. It is concluded that H1 probably does not suppress cell proliferation.

Animals↗
PubMedDate not supplied

[Epidemic human fascioliasis. Cuba 1983. VI. Clinical study of 40 children in the Hospital Provincial of Sagua la Grande].

We studied forty children with "Febrile-eosinophilic-Syndrome". They presented Fasciola Hepatic infection confirmed by: Fever, high eosinophils and abdominal pain. 82% used to eat watercress. All of them had positive biopsies-laparoscopies-intradermo-reaction and also reaction to Fasciola antigen. We present the results of and epidemic in Cuba during 1983.

Adolescent↗