Particle production from symmetry breaking after inflation and leptogenesis

Recent studies suggest that the process of symmetry breaking after inflation typically occurs very fast, within a single oscillation of the symmetry-breaking field, due to the spinodal growth of its long-wave modes, otherwise known as `tachyonic preheating'. We show how this sudden transition from the false to the true vacuum can induce a significant production of particles, bosons and fermions, coupled to the symmetry-breaking field. We find that this new mechanism of particle production in the early Universe may have interesting consequences for the origin of supermassive dark matter and the generation of the observed baryon asymmetry through leptogenesis.Comment: 17 pages, 2 figures. Significantly enlarged version, including a more detailed discussion of leptogenesis. To appear in Physics Letters

Ceramide generated by acidic sphingomyelinase contributes to tumor necrosis factor-α-mediated apoptosis in human colon HT-29 cells through glycosphingolipids formation Possible role of ganglioside GD3

AbstractIn the present study we assessed the contribution of acidic sphingomyelinase (ASMase), a ceramide generating enzyme, in tumor necrosis factor (TNF)-mediated apoptosis in human colon HT-29 cells. TNF induced apoptosis in HT-29 cells in a time- and dose-dependent fashion. Downregulation of the active endogenous ASMase form prevented TNF-stimulated ASMase activity and apoptosis. Furthermore, inhibition of glucosylceramide synthase, which blunted TNF-stimulated GD3 levels, abolished TNF-mediated cell death. Immunocytochemical staining revealed the co-localization of GD3 with mitochondria induced by TNF. The knockdown of targeted GD3 synthase by antisense expression vector protected HT-29 cells against TNF-induced cell death. Thus, ASMase plays a key role in TNF-induced cell death in human colon epithelial cells possibly through GD3 generation

The anatomy of the fruit in relation to the propensity of citrus species to split

The anatomy of the fruit has been compared in three prone-to-split mandarin hybrids (Nova, Ellendale and Murcott), several cultivars of clementine mandarin (Fino, Clementina de Nules and Orogrande), and in Owari satsuma mandarin. The fruit of the hybrids is oblate to subglobose and usually presents an open stylar end disrupted by a navel formed by the floral meristem, which is conserved near the apex of the fruit. In the non-prone-to-split clementines as well as in Owari satsuma, the floral axis protrudes inside the style, and the flower meristem is lost through abscission shortly after petal fall. The abaxial side of the carpels fuses with the flower axis forming at the stylar end of the fruit a solid tissue which externally has a small scar at the place of style abscission. Most of the fruits in these cultivars have no navel. In addition, the fruit of clementine is slightly oblate or globose. The relevance of these anatomical characteristics as regards to splitting is supported by the differences between the split and non-split fruits in Nova, the split fruit being more oblate in shape and having a bigger navel than non-split fruit. However, the effect of applied growth regulators on fruit splitting could not be correlated with their effect on the anatomy of the fruit. Additional factors not contemplated in the study also influence fruit splitting

Changes in cannabinoid receptor binding and mRNA levels in several brain regions of aged rats

AbstractWe have recently found that cannabinoid receptor binding and gene expression markedly decreased in extrapyramidal structures of aged rats. The present study was designed to analyze the possible existence of similar aging-induced changes in cannabinoid receptor binding and gene expression in brain regions other than extrapyramidal areas, but that also contain a significant population of cannabinoid receptors, such as the cerebellum, hippocampal structures, limbic and hypothalamic nuclei, the cerebral cortex and others. To this end, we analyzed cannabinoid receptor binding, using autoradiography, and cannabinoid receptor mRNA levels, using in situ hybridization, in slide-mounted brain sections obtained from young (3 month old) and aged (>2 year old) rats. Results were as follows. In the cerebellum, aged rats exhibited a marked decrease in cannabinoid receptor binding in the molecular layer (−33.3%), although accompanied by no changes in mRNA levels in the granular layer. In the cerebral cortex, a small, although statistically significant, decrease in binding was found in the deep layer (VI) (−18.3%) of aged rats, whereas no changes were found in the superficial layer (I). As in the case of the cerebellum, mRNA levels did not change in the cerebral cortex layers (II–III and V–VI). The different regions of the Ammon’s horn of the hippocampus exhibited similar cannabinoid receptor binding levels in aged and young rats. Interestingly, mRNA levels decreased in aged rats to a small, but statistically significant, extent (CA1: −26.1%; CA2: −21.6%; CA3: −14.4%). This was also seen in another hippocampal structure, the dentate gyrus (−14.6%), although in this region binding levels increased in aged rats (+28.4%). Two hypothalamic structures, the arcuate nucleus and the ventromedial hypothalamic nucleus, exhibited decreased cannabinoid receptor binding in aged rats (−31.1% and −30.3%, respectively), but this was not seen in the medial preoptic area. This was accompanied by no changes in mRNA levels in the ventromedial hypothalamic nucleus. In the limbic structures, aged rats exhibited similar binding levels to young rats. This was seen in the nucleus accumbens, septum nuclei and basolateral amygdaloid nucleus. However, mRNA levels slightly decreased in the basolateral amygdaloid nucleus (−13.4%), whereas they were not altered in the septum nuclei. Finally, other brain structures, such as the central gray substance and the brainstem, exhibited similar binding levels in aged and young rats. However, it is important to note that mRNA levels increased significantly (+211.2%) in the brainstem of aged rats, an area where the levels of binding and mRNA were very low in young rats. This marked increase may be related to an increase in the presence of glial elements in this region, as revealed by the increase in the immunoreactivity for glial fibrillary acidic protein observed in the brainstem of aged rats as compared to young animals. In summary, senescence was associated with changes in cannabinoid receptors in the cerebellum, the cerebral cortex, limbic and hypothalamic structures, the hippocampus and other brain regions. However, the changes observed (i) were not as marked and relevant as those early reported in extrapyramidal areas, and (ii) exhibited regional differences that might be attributed to the different roles played by these receptors in each region. Of particular relevance by their magnitude were the aging-induced decrease in binding found in the cerebellum and the hypothalamus, and the increase in mRNA levels observed in the brainstem. The latter might be related to an increase in the presence of glial cells which might contain cannabinoid receptor mRNA

The Polyakov loop and the heat kernel expansion at finite temperature

The lower order terms of the heat kernel expansion at coincident points are computed in the context of finite temperature quantum field theory for flat space-time and in the presence of general gauge and scalar fields which may be non Abelian and non stationary. The computation is carried out in the imaginary time formalism and the result is fully consistent with invariance under topologically large and small gauge transformations. The Polyakov loop is shown to play a fundamental role.Comment: 4 pages, REVTEX, no figure

DNA polymerase λ, a novel DNA repair enzyme in human cells

DNA polymerase lambda (pol λ) is a novel family X DNA polymerase that has been suggested to play a role in meiotic recombination and DNA repair. The recent demonstration of an intrinsic 5′-deoxyribose-5-phosphate lyase activity in pol λ supports a function of this enzyme in base excision repair. However, the biochemical properties of the polymerization activity of this enzyme are still largely unknown. We have cloned and purified human pol λ to homogeneity in a soluble and active form, and we present here a biochemical description of its polymerization features. In support of a role in DNA repair, pol λ inserts nucleotides in a DNA template-dependent manner and is processive in small gaps containing a 5′-phosphate group. These properties, together with its nucleotide insertion fidelity parameters and lack of proofreading activity, indicate that pol λ is a novel β-like DNA polymerase. However, the high affinity of pol λ for dNTPs (37-fold over pol β) is consistent with its possible involvement in DNA transactions occurring under low cellular levels of dNTPs. This suggests that, despite their similarities, pol β and pol λ have nonredundant in vivo functions.This work was supported by Ministerio de Ciencia y Tecnologı´a Grant BMC2000-1138, Comunidad Auto´noma de Madrid Grant 08.5/0063/2000 (to L. B.) and by an institutional grant from Fundacio´n Ramo´n Areces

Study on Nucleation Kinetics of Lysozyme Crystallization

The nucleation kinetics of hen egg-white lysozyme crystallization was investigated using a hot stage cooling crystallizer and a microscope to monitor the solution crystallization process in real time. Images of crystals were continuously recorded under varied precipitant and protein concentrations. The nucleation rate was found to be higher at higher precipitant concentration, and increase monotonically with protein concentration if the precipitant concentration was held constant. Attempt was made to interpret the experimental data using classical nucleation theory. It was found that the model predictions are lower than the experimental values at low supersaturations but agree well with experimental data at high supersaturations. The trends in the experimental data suggest that two nucleation mechanisms might co-exist: heterogeneous nucleation seeming to be the dominant at low supersaturation while at higher supersaturation homogeneous nucleation seeming to play the major role

DNA polymerase lambda (Pol λ), a novel eukaryotic DNA polymerase with a potential role in meiosis

A new gene (POLL) encoding a novel DNA polymerase (Pol λ) has been identified at mouse chromosome 19. Murine Pol λ, consisting of 573 amino acid residues, has a 32 % identity to Pol β, involved in nuclear DNA repair in eukaryotic cells. It is interesting that Pol λ contains all the critical residues involved in DNA binding, nucleotide binding and selection, and catalysis of DNA polymerization, that are conserved in Pol β and other DNA polymerases belonging to family X. Murine Pol λ, overproduced in Escherichia coli, displayed intrinsic DNA polymerase activity when assessed by in situ gel analysis. Pol λ also conserves the critical residues of Pol β required for its intrinsic deoxyribose phosphate lyase (dRPase) activity. The first 230 amino acid residues of Pol λ, that have no counterpart in Pol β, contain a BRCT domain, present in a variety of cell-cycle check-point control proteins responsive to DNA damage and proteins involved in DNA repair. Northern blotting, in situ hybridization analysis and immunostaining showed high levels of Pol λ specifically expressed in testis, being developmentally regulated and mainly associated to pachytene spermatocytes. These first evidences, although indirect, suggest a potential role of Pol λ in DNA repair synthesis associated with meiosis.This work has been granted by DGES (PB97-1192) and CAM (08.1/0044/98) to LB; CAM(08.1/0044.2/98) to AB; DGICYT (PB 95-0119), EC PL96-0183 and CAM (07/0022) to JM, and by an institutional grant from Fundación Ramón Areces