Constitutive heterochromatin: a surprising variety of expressed sequences

The organization of chromosomes into euchromatin and heterochromatin is amongst the most important and enigmatic aspects of genome evolution. Constitutive heterochromatin is a basic yet still poorly understood component of eukaryotic chromosomes, and its molecular characterization by means of standard genomic approaches is intrinsically difficult. Although recent evidence indicates that the presence of transcribed genes in constitutive heterochromatin is a conserved trait that accompanies the evolution of eukaryotic genomes, the term heterochromatin is still considered by many as synonymous of gene silencing. In this paper, we comprehensively review data that provide a clearer picture of transcribed sequences within constitutive heterochromatin, with a special emphasis on Drosophila and humans.     

Vgamma9/Vdelta2 T lymphocytes in Italian patients with Behçet's disease: evidence for expansion,and tumour necrosis factor receptor II and interleukin-12 receptor beta1 expression in active disease

Beh?et's disease is a multisystem disease in which there is evidence of immunological dysregulation. It has been proposed that gamma/delta T cells are involved in its pathogenesis. The aim of the present study was to assess the capacity of gamma/delta T cells with phenotype Vgamma9/Vdelta2, from a group of Italian patients with Beh?et's disease, to proliferate in the presence of various phosphoantigens and to express tumour necrosis factor (TNF) and IL-12 receptors. Twenty-five patients and 45 healthy individuals were studied. Vgamma9/Vdelta2 T cells were analyzed by fluorescence activated cell sorting, utilizing specific monoclonal antibodies. For the expansion of Vgamma9/Vdelta2 T cells, lymphocytes were cultured in the presence of various phosphoantigens. The expression of TNF receptor II and IL-12 receptor beta1 was evaluated with the simultaneous use of anti-TNF receptor II phycoerythrin-labelled (PE) or anti-IL-12 receptor beta1 PE and anti-Vdelta2 T-cell receptor fluorescein isothiocyanate. There was a certain hierarchy in the response of Vgamma9/Vdelta2 T cells toward the different phosphoantigens, with the highest expansion factor obtained with dimethylallyl pyrophosphate and the lowest with xylose 1P. The expansion factor was fivefold greater in patients with active disease than in those with inactive disease or in control individuals. TNF receptor II and IL-12 receptor beta1 expressions were increased in both patients and control individuals. The proportion of Vgamma9/Vdelta2 T cells bearing these receptors was raised in active disease when Vgamma9/Vdelta2 T cells were cultured in the presence of dimethylallyl pyrophosphate. These results indicate that Vgamma9/Vdelta2 T cell activation is correlated with disease progression and probably involved in the pathogenesis.     

The significance of an increase in soluble interleukin-2 receptor level in colorectal cancer and its biological regulating role in the physiological switching of the immune response cytokine network from TH1 to TH2 and back

 Current research has still not clarified the biological role of soluble interleukin(IL)-2 receptor (sIL-2R) and the significance of its increase in the serum of colon cancer patients compared to healthy subjects. To address these questions at the immunological level in a group of patients and healthy subjects, we determined the sIL-2R level in the serum and its release from peripheral blood mononuclear cells (PBMC) as a function of tumour necrosis factor (TNF) α, IL-1α, IL-1β, IL-2, interferon (IFN) γ, IL-4, IL-6 and IL-10 levels in the serum and PBMC production; and PBMC proliferative responses to IL-2, IL-4 and anti-CD3 monoclonal antibody (CD3), variously combined. The level of sIL-2R in patients’ serum was higher than in healthy subjects and correlated with the stage of advancement. Moreover, while in healthy subjects the serum level of sIL-2R was not significantly correlated with other parameters, in patients it was positively related to IL-4, IL-6 and IL-10 serum levels, PBMC IL-4 production and to the PBMC proliferative response to CD3 and CD3+IL-2; it was negatively correlated to IL-2 serum level and IL-1β PBMC release. A negative connection between IFNγ serum level and the PBMC production of sIL-2R was also found. This suggests that the increase of sIL-2R in the serum of patients, compared to healthy subjects, is involved in the inappropriate expansion of the T helper (TH2) suppressive immune response, which we previously reported. The multivariate statistical method supported the above suggestions and we also found that, in healthy subjects, the up- and down-regulation of sIL-2R in the serum within the physiological ranges seems to have a regulating role in the relationships between TNFα, IFNγ and IL-4, IL-6, contributing to the operation of the cytokine network between TH1 and TH2 cells. However, in patients compared to healthy subjects the increased sIL-2R serum level seems to direct the immune response towards a suppressive type, which may be due to an alteration in the above-mentioned physiological regulating role. Received: 12 April 1997 / Accepted: 4 September 1997     

The small GTPase Rab13 regulates assembly of functional tight junctions in epithelial cells

Junctional complexes such as tight junctions (TJ) and adherens junctions are required for maintaining cell surface asymmetry and polarized transport in epithelial cells. We have shown that Rab13 is recruited to junctional complexes from a cytosolic pool after cell-cell contact formation. In this study, we investigate the role of Rab13 in modulating TJ structure and functions in epithelial MDCK cells. We generate stable MDCK cell lines expressing inactive (T22N mutant) and constitutively active (Q67L mutant) Rab13 as GFP-Rab13 chimeras. Expression of GFP-Rab13Q67L delayed the formation of electrically tight epithelial monolayers as monitored by transepithelial electrical resistance (TER) and induced the leakage of small nonionic tracers from the apical domain. It also disrupted the TJ fence diffusion barrier. Freeze-fracture EM analysis revealed that tight junctional structures did not form a continuous belt but rather a discontinuous series of stranded clusters. Immunofluorescence studies showed that the expression of Rab13Q67L delayed the localization of the TJ transmembrane protein, claudin1, at the cell surface. In contrast, the inactive Rab13T22N mutant did not disrupt TJ functions, TJ strand architecture nor claudin1 localization. Our data revealed that Rab13 plays an important role in regulating both the structure and function of tight junctions.     

Synthesis, structure and luminescence study of two cadmium(II) coordination polymers with hetero donor ligands: Expansion of network dimensionality from 2D to 3D through hydrogen bonding

Two coordination polymers of cadmium with formula [Cd(pyp)₂(H₂O)₂]_n (1) and {[Cd₂(pyzca)₃(atr)(H₂O)]·H₂O}_n (2) [pypH = 3-pyridinepropionic acid, pyzcaH = 2-pyrazinecarboxylic acid and atrH = 5-aminotetrazole] have been synthesized and structurally characterized by X-ray single crystal diffraction analysis. Both complexes display 2D structures that extend into a 3D network by means of hydrogen bonding. The crystal packing of both complexes is reinforced by π-π interactions between adjacent aromatic rings. The fluorescence study indicates intraligand π-π* charge transfer, which is the reason for emission in both the complexes.