Recombination hotspot activity of hypervariable minisatellite DNA requires minisatellite DNA binding proteins

Hypervariable minisatellite DNA repeats are found at tens of thousands of loci in the mammalian genome. These sequences stimulate homologous recombination in mammalian cells [Cell60:95–103]. To test the hypothesis that protein-DNA interaction is required for hotspot functionin vivo, we determined whether a second protein binding nearby could abolish hotspot activity. Intermolecular recombination between pairs of plasmid substrates was measured in the presence or absence of thecis-acting recombination hotspot and in the presence or absence of the secondtrans-acting DNA binding protein. Minisatellite DNA had hotspot activity in two cell lines, but lacked hotspot activity in two closely related cell lines expressing a site-specific helicase that bound to DNA adjacent to the hotspot. Suppression of hotspot function occurred for both replicating and non-replicating recombination substrates. These results indicate that hotspot activityin vivo requires site occupancy by minisatellite DNA binding proteins.     

Reduced mitochondrial coupling in vivo alters cellular energetics in aged mouse skeletal muscle

The mitochondrial theory of ageing proposes that the accumulation of oxidative damage to mitochondria leads to mitochondrial dysfunction and tissue degeneration with age. However, no consensus has emerged regarding the effects of ageing on mitochondrial function, particularly for mitochondrial coupling (P/O). One of the main barriers to a better understanding of the effects of ageing on coupling has been the lack of in vivo approaches to measure P/O. We use optical and magnetic resonance spectroscopy to independently quantify mitochondrial ATP synthesis and O₂ uptake to determine in vivo P/O. Resting ATP demand (equal to ATP synthesis) was lower in the skeletal muscle of 30-month-old C57Bl/6 mice compared to 7-month-old controls (21.9 ± 1.5 versus 13.6 ± 1.7 nmol ATP (g tissue)⁻¹ s⁻¹, P = 0.01). In contrast, there was no difference in the resting rates of O₂ uptake between the groups (5.4 ± 0.6 versus 8.4 ± 1.6 nmol O₂ (g tissue)⁻¹ s⁻¹). These results indicate a nearly 50% reduction in the mitochondrial P/O in the aged animals (2.05 ± 0.07 versus 1.05 ± 0.36, P = 0.02). The higher resting ADP (30.8 ± 6.8 versus 58.0 ± 9.5 μmol g⁻¹, P = 0.05) and decreased energy charge (ATP/ADP) (274 ± 70 versus 84 ± 16, P = 0.03) in the aged mice is consistent with an impairment of oxidative ATP synthesis. Despite the reduced P/O, uncoupling protein 3 protein levels were not different in the muscles of the two groups. These results demonstrate reduced mitochondrial coupling in aged skeletal muscle that alters cellular metabolism and energetics.     

A voltage-dependent K+ current contributes to membrane potential of acutely isolated canine articular chondrocytes

The electrophysiological properties of acutely isolated canine articular chondrocytes have been characterized using patch-clamp methods. The 'steady-state' current–voltage relationship ( I–V ) of single chondrocytes over the range of potentials from −100 to +40 mV was highly non-linear, showing strong outward rectification positive to the zero-current potential. Currents activated at membrane potentials negative to −50 mV were time independent, and the I–V from −100 to −60 mV was linear, corresponding to an apparent input resistance of 9.3 ± 1.4 GΩ ( n = 23). The outwardly rectifying current was sensitive to the K⁺ channel blocking ion tetraethylammonium (TEA), which had a 50% blocking concentration of 0.66 m m (at +50 mV). The 'TEA-sensitive' component of the outwardly rectifying current had time- and membrane potential-dependent properties, activated near −45 mV and was half-activated at −25 mV. The reversal potential of the 'TEA-sensitive' current with external K⁺ concentration of 5 m m and internal concentration of 145 m m , was −84 mV, indicating that the current was primarily carried by K⁺ ions. The resting membrane potential of isolated chondrocytes (−38.1 ± 1.4 mV; n = 19) was depolarized by 14.8 ± 0.9 mV by 25 m m TEA, which completely blocked the K⁺ current of these cells. These data suggest that this voltage-sensitive K⁺ channel has an important role in regulating the membrane potential of canine articular chondrocytes.     

Hypoxic pulmonary vasoconstriction is heterogeneously distributed in the prone dog

Hypoxic pulmonary vasoconstriction (HPV) is thought to protect gas exchange by decreasing perfusion to hypoxic regions. However, with global hypoxia, non-uniformity in HPV may cause over-perfusion to some regions, leading to high-altitude pulmonary edema. To quantify the spatial distribution of HPV and regional PO2 (PRO2) among small lung regions (approximately 2.0 cm3), five prone beagles (approximately 8.3 kg) were anesthetized and ventilated (PEEP approximately 2 cm H2O) with an F1O2 of 0.21, then 0.50, 0.18, 0.15, and 0.12 in random order. Regional blood perfusion (Q), ventilation (VA) and calculated PRO2 were obtained using iv infusion of 15 microm and inhalation of 1 microm fluorescent microspheres. Lung pieces were clustered by their relative blood flow response to each F1O2. Clusters were shown to be spatially grouped within animals and across animals. Lung piece resistance increased as PRO2 decreased to 60-70 mmHg but dropped at PRO2's < 60mmHg. Regional ventilation changed little with hypoxia. HPV varied more in strength of response, rather than PRO2 response threshold. In initially homogeneous VA/Q lungs, we conclude that HPV response is heterogeneous and spatially clustered.     

Neural progenitor cells lack immunogenicity and resist destruction as allografts

Multipotent, self-renewing stem and progenitor cells isolated from the mammalian central nervous system (CNS) have been shown to survive as allografts following transplantation to sites throughout the neuraxis. However, studies of this type shed little light upon the immunologic properties of the cells themselves, primarily because little is learned about the intrinsic immunogenic properties of a cell when it is grafted into an immune-privileged site. We have therefore investigated the immunogenic and antigenic properties of CNS progenitor cells by grafting them into a conventional (i.e., non-immune-privileged) site, namely, beneath the kidney capsule. Our results indicate that allogeneic CNS progenitor cells survive at least 4 weeks in a conventional site, during which time they neither sensitize their hosts nor express detectable levels of major histocompatibility complex (MHC) class I or II. These in vivo data are in accord with flow cytometric results showing that CNS progenitor cells do not express MHC class I or class II, either at baseline or upon differentiation in 10% serum. Exposure to interferon gamma, however, reversibly upregulates expression of these key transplantation antigens. Together, these results reveal CNS progenitor cells to possess inherent immune privilege. Since CNS progenitor cell allografts were rejected beneath the kidney capsule following specific sensitization of the host, CNS progenitor cells were able to display alloantigens, albeit not in an immunogenic form.     

An animal model of SARS produced by infection of Macaca mulatta with SARS coronavirus

A new SARS animal model was established by inoculating SARS coronavirus (SARS-CoV) into rhesus macaques (Macaca mulatta) through the nasal cavity. Pathological pulmonary changes were successively detected on days 5-60 after virus inoculation. All eight animals showed a transient fever 2-3 days after inoculation. Immunological, molecular biological, and pathological studies support the establishment of this SARS animal model. Firstly, SARS-CoV-specific IgGs were detected in the sera of macaques from 11 to 60 days after inoculation. Secondly, SARS-CoV RNA could be detected in pharyngeal swab samples using nested RT-PCR in all infected animals from 5 days after virus inoculation. Finally, histopathological changes of interstitial pneumonia were found in the lungs during the 60 days after viral inoculation: these changes were less marked at later time points, indicating that an active healing process together with resolution of an acute inflammatory response was taking place in these animals. This animal model should provide insight into the mechanisms of SARS-CoV-related pulmonary disease and greatly facilitate the development of vaccines and therapeutics against SARS.     

Immunological consequence of renal transplantation and immunosuppression. I. Alterations in human natural killer-cell activity

The role and activity of natural killer (NK) cells following renal transplantation remain unknown. To monitor NK activity, a⁵¹Cr release of K-562 targets in prednisone-and azathioprine-treated patients receiving renal allografts was utilized. In 18 patients in whom NK activity was measured prior to and after transplantation, a significant diminution in NK activity within 3 weeks following transplantation was demonstrated compared to pretransplant values (34.71 vs 12.20%, respectively;P<0.001). In 11 subjects who had NK activity assayed at various intervals after transplantation but not prior to allografting, mean NK values were markedly lower (mean, 14.2%) than those of normal volunteers or patients maintained on hemodialysis (P<0.001). The latter two control groups demonstrated no difference (P = NS) in mean NK activity (39.46 vs 35.82%, respectively). In 5 of the 29 patients evaluated with good long-term graft function (mean, 2.7 years), restitution of normal NK activity was demonstrated. In two patients with bacterial infections, NK activity increased from 39.29 to 51.7% and from 13.54 to 20.00%. After infection, these values were 35.3% in the former and 3.39% in the latter. Viral infection did not appear to affect NK activity significantly. NK activity was increased in only one of seven patients with documented rejection episodes. In three of such patients, NK activity declined significantly following pulse methylprednisolone therapy. These results indicate that (1) NK-cell activity significantly decreases immediately after transplantation, probably as a result of immunosuppressive therapy; (2) NK activity does not appear to be stimulated by the alloreactive rejection process; (3) NK activity may be augmented in the course of bacterial but not viral infections; and (4) long-term allograft survival may be associated with a restoration of NK-cell levels in certain recipients.     

The aniridia-Wilms tumor association: The critical role of chromosome band 11p13

The role of del (11)(p13) as a cause of aniridia, with and without Wilms tumor, is strengthened by demonstration of this chromosome aberration in 3 patients: monozygous twin girls, both of whom have aniridia and mental retardation and one of whom has a Wilms tumor; and an unrelated boy with aniridia and ambiguous genitalia. The break points defining the interstitial deletion for the twins are 11p13 and 11p15.1, while for the boy they are 11p1302 and 11p14.1. These patients and their karyotypes substantiate the critical importance of chromosome band 11p13 (or its hemizygous representation) in the development of aniridia and an associated Wilms tumor diathesis, as had been suggested previously (Riccardi VM, Sujansky E, Smith AC, Francke U, (1978): Pediatrics 61, 604-610).