Recent statistical analysis of the folding of G0/G1 chromosomes using fluorescence in situ hybridization (FISH) allowed development of a random walk/giant loop model of chromosome structure. According to this model there are two levels of organization of G0/G1 chromosome fibres. On the first level, the fibres are arranged in giant loops several Mbp in size, and within each loop the fibres are randomly folded. On the second level, the loop attachment sites form a chromosome backbone that also shows random folding. Newly replicated segments of mammalian chromosomes may be directly visualized at high resolution in S-phase nuclei using immunofluorescent methods and appear as worm-like fibres. In our earlier study, we analysed conformation of the fibres in human cells blocked for 16 h at the G1/S boundary with 5- fluorodeoxyuridine (FdU) and then released into S-phase by the addition of a DNA prec ursor. However, long treatment of cells with FdU induces very short replicons and may promote apoptosis. In this study we analysed conformation of the fibres in normally proliferating human cells that had not been blocked with FdU for a long time. It has been found that replicated chromosome fibres visualized just after 2 h of incubation of the cells with a non-radioactively labelled DNA precursor behave as flexible polymer chains without major constraints, and that their local conformation in the range of several microns of their contour length may be considered as random. Confocal analysis of human X chromosomes visualized in HeLa cells using FISH with a specific painting probe shows that in S-phase the chromosomes occupy distinct nuclear territories and their apparent size does not differ from that in non-S-phase cells. This observation indicates that the second level of chromosome organization also exists in S-phase chromosomes. It appears, theref ore, that the random walk/giant loop model developed earlier for G0/G1 chromosomes is also valid for S-phase chromosomes. 相似文献
The introduction of highly active antiretroviral therapy (HAART) has resulted in marked reductions in mortality and acquired
immunodeficiency syndrome (AIDS) incidence across all risk groups; however, the proportionate decrease among injecting drug
users (IDUs) has been less impressive. Much of the disparity in benefit to IDUs has been a consequence of decreased access
to and receipt of potent antiretroviral combinations. Strategies to increase access to and utilization of HAART have included
entry into drug treatment and abstinence. Unfortunately, as few as 15%–20% of active drug users in the United States, and
in many other countries, are in drug treatment at any one time. We report a pilot project among out-of-drug treatment IDUs
infected with human immunodeficiency virus (HIV); HIV therapy was successfully provided to active heroin injectors using the
Community Health Care Van (CHCV) at sites of needle exchange. Subjects were willing to initiate, but were not receiving, recommended
HIV therapy and were not interested in formal drug treatment. Antiretroviral therapy regimens were selected and linked to
heroin injection timing. Weekly visits were scheduled by CHCV staff to assess adverse side effects and encourage adherence.
Of the 13 participants, the mean baseline HIV-1 RNA level and CD4 lymphocyte count were 162,369 (log 5.21) copies per milliliter
and 265 cells per milliliter, respectively. By 6 months, the proportion whose HIV-1 RNA was below the limits of detection
(<400 copies/mL) was 85% (N=11); 77% (N=10) had nondetectable levels by 9 months. By 12 months, 54% (N=7) had a persistently
nondetectable viral load, and the net increase in CD4 lymphocyte count was 150 cells per milliliter. As an additional and
unintended benefit of this pilot project, 9 (69%) subjects chose to enter drug treatment after achieving a nondetectable viral
load. Entry into drug treatment was associated with durability of viral suppression. This small pilot study suggests that
health services based on needle exchange may enhance access to HAART among out-of-treatment HIV-infected IDUs. In addition,
it demonstrates that this population can benefit from this therapy with the support of a nontraditional, community-based health
intervention. 相似文献
Background: The role of adjuvant postoperative radiotherapy for locally advanced colon cancer is not well documented.
Methods: Seventy-eight patients who underwent a complete resection of B2-C colon cancer received postoperative radiotherapy. Twenty-eight
patients received ⩽45 Gy; 50 patients received 50–55 Gy. Twenty-seven patients received adjuvant fluorouracil-based chemotherapy.
All patients were followed for a minimum of 3 years; no patients were lost to follow-up.
Results: The overall local control rate was 88%. The 5-year actuarial rate of local control was 96% after 50–55 Gy postoperative radiotherapy
compared with 76% after <50 Gy (p=0.0095). Multivariate analysis of local control showed that only radiotherapy dose significantly
influenced this end point. Cause-specific survival rates at 5 years were B2, 67%; B3, 90%; C1, 100%; C2, 61%; C3, 36%; and
overall, 63%. Multivariate analysis of cause-specific survival showed that only stage significantly influenced this end point.
Bowel obstruction caused by adhesions developed in three patients and required a laparotomy; radiation-induced sarcoma developed
in one additional patient.
Conclusions: Postoperative radiotherapy appears to reduce the risk of local recurrence in patients with locally advanced colon cancer.
The optimal dose is probably 50–55 Gy at 1.8 Gy per fraction. Postoperative radiotherapy may improve cause-specific survival
for patients with stages B3 and C2 cancers. 相似文献
Interpretation of first-pass myocardial perfusion studies employing bolus administration of T1 magnetic resonance (MR) contrast agents requires an understanding of the relationship between contrast concentration and image pixel intensity. The potential effects of myocardial water exchange rates among the intravascular, interstitial, and cellular compartments on this relationship are controversial. We directly studied these issues in isolated, nonbeating canine interventricular septa. Myocardial T1 was measured three times/s during bolus transit of intravascular (albumin-Gd-DTPA and poly-lysine-Gd-DTPA) and extracellular (gadoteridol) contrast agents. For polylsine-Gd-DTPA, the peak changes in myocardial 1/T1 (ΔR1) scaled nonlinearly with perfusate contrast concentration whereas a linear relationship would be expected for fast water exchange among the vascular, interstitial, and cellular compartments. For all agents, the peak ΔR1 were much smaller than the values expected on the basis of fast myocardial water exchange. The data demonstrate that in isolated myocardial tissue, myocardial T1 enhancement during bolus administration of contrast can be strongly affected by myocardial water exchange for both intravascular and extracellular MR contrast agents. 相似文献
The acute toxicity of inhaled eugenol was assessed by exposure of three groups of five male and five female rats to a submicron aerosol of eugenol for 4 h followed by a 14-day observation period. A fourth group, also of five male and five female rats and exposed to air only under similar conditions, served as a control group for comparison. The three concentrations of eugenol to which the different groups were exposed were 2.58, 1.37 and 0.77 mg/l. The mass median aerodynamic diameters and geometric standard deviations of the aerosols were, respectively, 0.82 m (g 2.26), 0.88 m (g 2.05) and 0.9 m (g 1.87). Clinical signs observed during exposure consisted principally of moderately increased salivation and restlessness (indicative of irritation) and abnormal breathing patterns. The signs were graded, being less marked in animals exposed to the lower concentrations of eugenol. All three groups, exposed to high, medium and low levels of eugenol, lost weight overnight following exposure. Associated with the weight loss were marked reductions in food and water intake. The responses appeared to be largely independent of the concentration of eugenol inhaled, although there was some evidence of a graded effect on water intake. There was rapid recovery, with food and water consumption data comparable with control values throughout most of the remainder of the 14-day observation period. Also, by the end of the observation period, group mean body weights were comparable. Upon sacrifice and macroscopic examination of the animals, abnormalities were detected in the lungs only of a few animals: 3/10 control, 2/10 eugenol 2.58 mg/l, and 2/10 eugenol 0.77 mg/l. These consisted of dark red/red (raised) areas up to 4×4 mm. Such abnormalities are not uncommon in the lungs of laboratory maintained rats and their presence with equal incidence in control animals suggests that they are unlikely to be related to inhalation of eugenol. Lung weight to body weight ratio values for all groups were similar, providing no evidence of any persistent effect of eugenol on the lungs of the rats. Similarly, histopathological examination of the lung failed to reveal any treatment-related changes. A few incidental lesions present were considered spontaneous in origin and therefore of no toxicological importance. 相似文献
The ultrastructure of the avian Golgi tendon organ (GTO) is described and compared with those of mammals using transverse sections through the myo-tendinous junctions of wing muscles of adult mallard ducks. The capsule, which is continuous with the perineural epithelial sheath of the Ib afferent nerve fiber, consists of four to seven flattened cellular lamellae. Two to four muscle fibers attach to large collagen bundles which enter the GTO through a tight collar at the proximal end of the fusiform capsule. These collagen bundles divide into many smaller bundles, which run longitudinally through the lumen in compartments formed by septal cells. The septal cells contain many prominent lipid accumulations. The Ib axon divides several times, and the unmyelinated branch axons weave between the small collagen bundles. Schwann cell processes or basement membrane usually intervene between the axons and collagen bundles. The small collagen bundles regroup into larger bundles, which pass through tight capsular collars and merge with the main muscle tendon. The size of the duck GTOs was measured and found to be smaller than the GTOs of man, cat or rat. 相似文献
Lung surfactant lowers surface tension and adjusts interfacial rheology to facilitate breathing. A novel instrument, the interfacial stress rheometer (ISR), uses an oscillating magnetic needle to measure the shear viscosity and elasticity of a surfactant monolayer at the air-water interface. The ISR reveals that calf lung surfactant, Infasurf, exhibits remarkable fluidity, even when exposed to air pollution residual oil fly ash (ROFA), hydrogen peroxide (H2O2), or conditioned media from resting A549 alveolar epithelial cells (AEC). However, when Infasurf is exposed to a subphase of the soluble fraction of ROFA- or H2O2-treated AEC conditioned media, there is a prominent increase in surfactant elasticity and viscosity, representing two-dimensional gelation. Surfactant gelation is decreased when ROFA-AEC are pretreated with inhibitors of cellular reactive oxygen species (ROS), or with a mitochondrial anion channel inhibitor, as well as when A549-rho0 cells that lack mitochondrial DNA and functional electron transport are investigated. These results implicate both mitochondrial and nonmitochondrial ROS generation in ROFA-AEC-induced surfactant gelation. A549 cells treated with H2O2 demonstrate a dose-dependent increase in lung surfactant gelation. The ISR is a unique and sensitive instrument to characterize surfactant gelation induced by oxidatively stressed AEC. 相似文献
During development, discrete cell fates often result from variation in the intensity of a particular signal. The mechanisms underlying these seemingly analog-to-digital switches are not understood. In developing T lymphocytes, low-intensity signals through the antigen receptor result in positive selection while more intense signals give rise to negative selection. By deleting the genetic locus encoding the regulatory B1 subunit of calcineurin specifically in thymocytes, we found an absolute requirement for calcineurin in positive selection. In contrast, calcineurin activity was dispensable in several models of negative selection. Unexpectedly, we found that removal of calcineurin activity from thymocytes results in inefficient ERK activation at the double-positive stage of thymocyte development, when selection occurs. These studies clarify the mechanism by which graded signals are converted to discrete outcomes in T cell development and further indicate that the developmental roles of calcineurin likely contribute to immunosuppression by calcineurin inhibitors. 相似文献
1. The increment threshold for a brief, small probing light flash was used as an indicator of the state of adaptation of the human fovea. It shows that illumination of a zone up to 7 min of arc in diameter desensitizes the retina and that the additional illumination of a surrounding zone acts to counteract the desensitization.
2. The red and green colour mechanisms were isolated by selecting light of appropriate wave-lengths for the adaptation and the increment stimuli and it was demonstrated that the desensitizing and sensitizing adaptation zones exist within each mechanism.
3. Using the constancy of the increment threshold for a brief, small probing flash as a null-indicator for equivalence of annuli of various wave-lengths to produce a given amount of sensitization, the action spectrum for the laterally interacting region was obtained for both the red and the green mechanisms.
4. For the red mechanism, the surrounding sensitizing zone has the action spectrum also of the red mechanism. For the green mechanism the surrounding sensitizing zone has a green action spectrum.
Leishmania donovani is an important intracellular protozoal pathogen of humans, which resides solely within mononuclear phagocytes. Phase-contrast microscopy and cinemicroscopy were used to examine the interaction of L. donovani promastigotes with human phagocytes to characterize and quantitate the sequence of events that results in leishmanial infection. 相似文献