A cruciform-dumbbell model for inverted dimer formation mediated by inverted repeats

Small inverted repeats (small palindromes) on plasmids have been shown to mediate a recombinational rearrangement event in Escherichia coli leading to the formation of inverted dimers (giant palindromes). This recombinational rearrangement event is efficient and independent of RecA and RecBCD. In this report, we propose a cruciform-dumbbell model to explain the inverted dimer formation mediated by inverted repeats. In this model, the inverted repeats promote the formation of a DNA cruciform which is processed by an endonuclease into a linear DNA with two hairpin loops at its ends. Upon DNA replication, this linear dumbbell-like DNA is then converted to the inverted dimer. In support of this model, linear dumbbell DNA molecules with unidirectional origin of DNA replication (ColE1 ori ) have been constructed and shown to transform E.coli efficiently resulting in the formation of the inverted dimer. The ability of linear dumbbell DNA to transform E.coli suggests that the terminal loops may be important in bypassing the requirement of DNA supercoiling for initiation of replication of the ColE1 ori.     

Expression of fibronectin splicing variants in organ transplantation: a differential pattern between rat cardiac allografts and isografts

Allograft rejection is associated with infiltration of inflammatory cells and deposition of extracellular matrix proteins. The extent to which diversity in the extracellular matrix regulates inflammatory cell function in transplants remains unclear. One group of extracellular matrix proteins, termed fibronectins (FNs), exhibits inherent diversity as a consequence of alternative splicing in three segments: EIIIA, EIIIB, or V. Although the EIIIA segment has documented functions in mesenchymal cell differentiation, neither this segment nor the EIIIB segment have been tested for effects specific to leukocyte functions. By contrast, the V region can include the CS-1 segment to which leukocytes may adhere through alpha 4 beta 1 integrins. In this study, we demonstrate that EIIIA+, EIIIB+, and V+ FN variants are synthesized, primarily by macrophages in distinct temporal and spatial patterns in two rat cardiac transplant models: either with antigenic challenge, allografts, or without challenge, isografts. The ratio of EIIIA inclusion into FN increases by day 1 in allografts and isografts and remains high until allografts are rejected (approximately 7 days) but falls to normal levels in tolerated isografts (day 6). EIIIB+ FN ratios in allografts peak later than do EIIIA+ FNs (day 4). EIIIB+ FN ratios remain relatively low in isografts. Interestingly, EIIIA+ and EIIIB+ FNs are deposited prominently in the myocardium of rejecting allografts in close association with infiltrating leukocytes, and FN expression and deposition are prominent at sites of infarction. By contrast, these FNs are largely restricted to the epicardium and to a lesser degree in the immediately adjacent myocardium in isografts. CS-1+ FNs increase in allografts and isografts at 3 hours after transplantation but are particularly prominent in allografts 1 to 3 days before rejection. Our data suggest that FN splicing variants have a differential role in the effector functions of leukocytes in allografts and isografts and provide a foundation for testing their function on leukocytes and a rationale for FN-based therapeutics to modulate allograft rejection in transplant recipients.     

Psychosocial experiences influence functioning: new risks, new outcomes

A 34-year-old Japanese woman developed spiking fever, splenomegaly, arthritis, neutrophilia, hyperferritinaemia (22517 ng/ml), elevated C-reactive protein (9.1 mg/ml) and severe thrombocytopenia (1.7 x 10(4)/microl). The patient had depressed antithrombin III activity and abnormally high concentrations of both fibrin degradation products and thrombin-antithrombin complexes. This condition was resistant to high-dose prednisolone therapy (120 mg/day) and non-steroidal anti-inflammatory drugs. We initiated oral methotrexate therapy (7.5 mg/week, orally) with a favourable outcome. The patient's spiking fever subsided on the first day of methotrexate administration. Elevated levels of ferritin and C-reactive protein in the sera rapidly normalised. Methotrexate rapidly improved the disease state which suggested that methotrexate act via modulation of cytokine production or secretion.     

Multiple pathways are involved in the extracellular processing of MHC class I-restricted peptides

T cell stimulation by certain class I-restricted antigenic peptides, such as the HIV 1 gp160-derived peptide, P18, requires peptide processing by angiotensin-1 converting enzyme (ACE) in FCS. We observed that longer versions of P18 and the murine cytomegalovirus pp89-derived core peptide, pMCMV, which could stimulate T cell hybridomas in FCS, were not as sensitive to the ACE inhibitor captopril as P18. Using cell-free soluble murine class I MHC molecules and protease inhibitors, we found that there are pathways of differing efficiency that use enzymes other than ACE for the proteolytic processing of peptides in serum. The kinetics of the generation of T cell stimulatory activity among P18 variant peptides in serum differed with peptide length, and with the nature of amino and COOH-terminal extensions. Such processing occurs in human plasma as well as in FCS. The understanding of this processing, its kinetics, and its inhibitors can lead to better design of peptide-based therapies, including vaccines.     

Comparison between morphologic changes seen on high-resolution CT and regional pulmonary perfusion seen on SPECT in patients with cystic fibrosis

OBJECTIVE: To evaluate the relationship between morphologic findings seen on high-resolution computed tomography (HRCT) of the lung and regional lung perfusion depicted on single photon-emission computed tomography (SPECT) pulmonary perfusion imaging in patients with cystic fibrosis. MATERIALS AND METHODS: Ten HRCT and 10 technetium-99 m macroaggregated albumin SPECT pulmonary perfusion imaging studies were performed on eight young adult patients who were considered to be clinically well and have mild to moderate cystic fibrosis. HRCT scans of the chest were evaluated using a CT scoring system which included grading of bronchiectasis, peribronchial thickening, hyperlucency, bullae, collapse/consolidation, and mucus plugging. Each lung was divided into six anatomic zones which were independently scored. A lung perfusion score (between 0 and 100), reflecting the percentage of compromised lung, was estimated for each zone. Axial lung perfusion SPECT images were matched anatomically to HRCT images. Lung function was considered compromised when the counts per pixel were less than 25 % of the count level seen in an area of the same patient's lung which was judged to be normal. RESULTS: There was a statistically significant relationship (P = 0.0001) between HRCT total scores and SPECT lung perfusion scores as well as between hyperlucency scores by HRCT and the SPECT lung perfusion scores. However, the HRCT score was a poor predictor of the lung perfusion score in zones with intermediate HRCT scores, which constituted 106 of 120 zones. CONCLUSION: Morphologic changes depicted by HRCT correlate with decreased lung pefusion on SPECT. However, HRCT changes accurately predict regional lung function only in the most normal and severely diseased lung zones.     

Experimental treatment of brain tumor cells using CD suicide gene

Pro-opiomelanocortin (POMC) is a polyhormone precursor produced predominantly in the pars distalis and pars intermedia of the pituitary gland where it undergoes tissue specific processing to produce a whole array of peptides. We have shown previously that peptides derived from the N-terminal region of POMC are involved in adrenal growth in rats. Using specific two site immunoradiometric assays we have found that the plasma of 17 week old fetal sheep contain a 50 fold excess of pro-gamma-MSH over ACTH. As term approached, the levels of pro-gamma-MSH fell and ACTH rose with evidence of fragmentation of pro-gamma-MSH, suggesting that these peptides act in concert in the development of the fetal adrenal cortex and also provide the necessary drive to bring about parturition. In an attempt to explore the pathophysiology of adrenal function we have cloned human POMC cDNA which led to the discovery of a 9bp addition/deletion mutation in the C-terminus of gamma 3-MSH between positions 67-73. Chinese hamster ovary cells (CHO) cells stably transfected with constructs containing the variant POMC cDNAs have shown a degree of partial processing. Work is currently underway to further investigate the effects of these mutations on the processing by the prohormone converting enzymes PC1 and PC2.