Optical Manipulation of Bipolarons in a System with Nonlinear Electron-Phonon Coupling.

We investigate full quantum mechanical evolution of two electrons nonlinearly coupled to quantum phonons and simulate the dynamical response of the system subject to a short spatially uniform optical pulse that couples to dipole-active vibrational modes. Nonlinear electron-phonon coupling can either soften or stiffen the phonon frequency in the presence of electron density. In the former case, an external optical pulse tuned just below the phonon frequency generates attraction between electrons and leads to a long-lived bound state even after the optical pulse is switched off. It originates from a dynamical modification of the self-trapping potential that induces a metastable state. By increasing the pulse frequency, the attractive electron-electron interaction changes to repulsive. Two sequential optical pulses with different frequencies can switch between attractive and repulsive interaction. Finally, we show that the pulse-induced binding of electrons is shown to be efficient also for weakly dispersive optical phonons, in the presence anharmonic phonon spectrum and in two dimensions.

[A bronchial polyp and foreign body in an adolescent]. / Polip i strano tijelo bronha u adolescenta.

A fifteen-year-old adolescent with recurrent pneumonia in the last two years is presented. The polyp in the lobar bronchus for the right inferior lobe and a foreign body in posterobasal segmental bronchus were found on bronchoscopy. The polyp (patHohistologically confirmed granulomatous tissue) and foreign body (thorny fruit of small caltrops, Tribulus terrestris) were extracted through a rigid ventilatory bronchoscope. The polyp presumably developed from the thorn of the fruit stuck in bronchial mucosa.

[BCG dissemination in a child with normal immunity]. / BCG diseminacija u djeteta s normalnom imunosti.

A fourteen month old girl with BCG dissemination and BCG lymphadenitis is presented. Mycobacterium bovis BCG strain was isolated from axillary fistula and from gastric contents. Pathohystological examination of the lymph mode and cytological examination of the bronchial mucus confirmed granulomatous inflammation. All tests for humoral and cellular immunity were with reference ranges. Antituberculous therapy successfully eliminated Mycobacterium bovis in gastric contents, and healed the wound in the left armpit. As the patient had tuberculoid form of BCG dissemination, the therapy was successful.

Plant DNA methyltransferases.

DNA methylation is an important modification of DNA that plays a role in genome management and in regulating gene expression during development. Methylation is carried out by DNA methyltransferases which catalyse the transfer of a methyl group to bases within the DNA helix. Plants have at least three classes of cytosine methyltransferase which differ in protein structure and function. The METI family, homologues of the mouse Dnmtl methyltransferase, most likely function as maintenance methyltransferases, but may also play a role in de novo methylation. The chromomethylases, which are unique to plants, may preferentially methylate DNA in heterochromatin; the remaining class, with similarity to Dnmt3 methyltransferases of mammals, are putative de novo methyltransferases. The various classes of methyltransferase may show differential activity on cytosines in different sequence contexts. Chromomethylases may preferentially methylate cytosines in CpNpG sequences while the Arabidopsis METI methyltransferase shows a preference for cytosines in CpG sequences. Additional proteins, for example DDM1, a member of the SNF2/SWI2 family of chromatin remodelling proteins, are also required for methylation of plant DNA.

Multiple DNA methyltransferase genes in Arabidopsis thaliana.

Methylation of plant DNA occurs at cytosines in any sequence context, and as the Arabidopsis methyltransferase, METI, preferentially methylates cytosines in CG dinucleotides, it is likely that Arabidopsis has other methyltransferases with different target specificities. We have identified five additional genes encoding putative DNA methyltransferases. Three of these genes are very similar to METI throughout the coding region; these genes probably arose by a series of gene duplication events, the most recent giving rise to METIIa and METIIb. METIIa and b are expressed at low levels in vegetative and floral organs and the level of transcripts is not affected by the introduction of a METI antisense transgene, nor do the METII enzymes substitute for the reduced activity of METI in methylating CG dinucleotides. METIII is not essential as it encodes a truncated protein. Two other genes encode a second class of DNA methyltransferase with the conserved motifs characteristic of cytosine methyltransferases, but with little homology to the METI-like methyltransferases through the remainder of the protein. These two methyltransferases are characterized by the presence of a chromodomain inserted within the methyltransferase domain, suggesting that they may be associated with heterochromatin. Both these genes are transcribed at low levels in vegetative and reproductive tissues.

DNA methylation and the promotion of flowering by vernalization.

We have tested the hypothesis that the promotion of flowering by prolonged exposure to low temperatures (vernalization) is mediated by DNA demethylation [Burn, J. E., Bagnall, D. J., Metzger, J. M., Dennis, E. S. & Peacock, W. J. (1993) Proc. Natl. Acad. Sci. USA 90, 287-291]. Arabidopsis plants that have reduced levels of DNA methylation because of the presence of a methyltransferase (METI) antisense gene flowered earlier than untransformed control plants, without the need for a cold treatment. Decreased DNA methylation mutants (ddm1) also flowered earlier than the wild-type progenitor under conditions where they respond to vernalization. We conclude that demethylation of DNA is sufficient to cause early flowering, and we have found that the promotion of flowering is directly proportional to the decrease in methylation in METI antisense lines. The early-flowering phenotype was inherited in sexual progeny, even when the antisense transgene had been lost by segregation. Methyltransferase antisense plants with low DNA methylation levels responded to a low-temperature treatment by flowering even earlier than their untreated siblings indicating that the promotion of flowering by cold and by demethylation was additive when neither treatment saturated the early-flowering response. As in untransformed control plants, the cold-induced early-flowering signal was reset in progeny of METI antisense plants. These observations suggest that the demethylation brought about by a METI antisense can account for some properties of vernalization, but not for the need for revernalization in each generation.

[Pulmonary hypoplasia]. / Hipoplazija pluca.

A thirteen month-old male child was hospitalized with left lung pneumonia. After pneumonia was cured the auscultatory signs persisted. Radiologically, left lung was hyperlucent with weak vascular markings. Perfusion scintigraphy showed lack of perfusion in the left lung. Bronchographically, decreased volume of the left lung and bronchiectasis were shown. Angiography revealed hypoplastic left pulmonary artery which was the cause of the dysgenesis of the left lung. All these findings pointed to pulmonary hypoplasia.

Epidermal growth factor-receptor expression correlates with tumor cell proliferation and prognosis in gastric cancer.

Currently, the most accurate prognostic indicator in gastric cancer is stage. Studies on proliferating cell nuclear antigen (PCNA) in gastric cancer have demonstrated that the PCNA labeling index correlates with depth of invasion, organ metastasis, vascular invasion, and tumor stage, suggesting that this marker may be a valuable prognostic factor. Epidermal growth factor (EGF) promotes the growth of cells of both ectodermal and mesodermal origin, and plays an important role in cellular proliferation and differentiation. Furthermore, there has been increasing evidence that growth factors and their receptors are involved in carcinogenesis. The aim of this study was to investigate the correlation between expression of the EGF-receptor (EGF-r) and proliferative activity (PCNA labeling index) in gastric cancer by immunohistochemical analysis. Our preliminary results on 56 gastric cancers indicate that the PCNA labeling index correlates with EGF-r immunoreactivity. Furthermore, survival was significantly lower in patients with EGF-r positive tumors and a high PCNA labeling index. These in situ observations suggest that EGF-r may play an important role in the growth regulation of human gastric carcinomas.