Highlights and discoveries from the Chandra X-ray Observatory

Within 40 years of the detection of the first extra-solar x-ray source in 1962, NASA's Chandra X-ray Observatory has achieved an increase in sensitivity of 10 orders of magnitude, comparable to the gain in going from naked-eye observations to the most powerful optical telescopes over the past 400 years. Chandra is unique in its capabilities for producing sub-arcsecond x-ray images with 100-200 eV energy resolution for energies in the range 0.08 < E < 10 keV, locating x-ray sources to high precision, detecting extremely faint sources, and obtaining high-resolution spectra of selected cosmic phenomena. The extended Chandra mission provides a long observing baseline with stable and well-calibrated instruments, enabling temporal studies over timescales from milliseconds to years. In this report we present a selection of highlights that illustrate how observations using Chandra, sometimes alone, but often in conjunction with other telescopes, have deepened, and in some instances revolutionized, our understanding of topics as diverse as protoplanetary nebulae; massive stars; supernova explosions; pulsar wind nebulae; the superfluid interior of neutron stars; accretion flows around black holes; the growth of supermassive black holes and their role in the regulation of star formation and growth of galaxies; impacts of collisions, mergers, and feedback on growth and evolution of groups and clusters of galaxies; and properties of dark matter and dark energy.

Stimulation of resorption in cultured mouse calvarial bones by thiazolidinediones

Dosage-dependent release of 45Ca was observed from prelabeled mouse calvarial bones after treatment with two thiazolidinediones, troglitazone and ciglitazone. Release of 45Ca by ciglitazone was decreased by the osteoclast inhibitors acetazolamide, calcitonin, 3-amino-1-hydroxypropylidene-1,1-bisphosphonate, and IL-4, but not affected by the peroxisome proliferator-activated receptor gamma antagonist, GW 9662, the mitotic inhibitor, hydroxyurea, or indomethacin. Enhanced expression of receptor activator of nuclear factor-kappaB ligand (RANKL) mRNA and protein and decreased osteoprotegerin (OPG) mRNA and protein were noted after ciglitazone treatment of calvariae. Ciglitazone and RANKL each caused increased mRNA expression of osteoclast markers: calcitonin receptor, tartrate-resistant acid phosphatase, cathepsin K, matrix metalloproteinase-9, integrin beta3, and nuclear factor of activated T cells 2. OPG inhibited mRNA expression of RANKL stimulated by ciglitazone, mRNA expression of osteoclast markers stimulated by ciglitazone and RANKL, and 45Ca release stimulated by troglitazone and ciglitazone. Increased expression of IL-1alpha mRNA by ciglitazone was not linked to resorption stimulated by the thiazolidinedione. Ciglitazone did not increase adipogenic gene expression but enhanced osteocalcin mRNA in calvariae. In addition to exhibiting sensitivity to OPG, data indicate that stimulation of osteoclast differentiation and activity by thiazolidinediones may occur by a nonperoxisome proliferator-activated receptor gamma-dependent pathway that does not require cell proliferation, prostaglandins, or IL-1alpha but is characterized by an increased RANKL to OPG ratio.

Ritscher-Schinzel cranio-cerebello-cardiac (3C) syndrome: report of four new cases and review

Ritscher-Schinzel syndrome, also known as the 3C syndrome, is a rare, autosomal recessive syndrome characterized by craniofacial, cerebellar, and cardiac anomalies. Cardiac manifestations include ventricular septal defect, atrial septal defect, tetralogy of Fallot, double outlet right ventricle, hypoplastic left heart, aortic stenosis, pulmonic stenosis and other valvular anomalies. Central nervous system anomalies include Dandy-Walker malformation, cerebellar vermis hypoplasia and enlargement of the cisterna magna. Craniofacial abnormalities seen are cleft palate, ocular coloboma, prominent occiput, low-set ears, hypertelorism, down-slanting palpebral fissures, depressed nasal bridge and micrognathia. Dandy-Walker malformation, posterior fossa cyst, hydrocephalus and congenital heart defect are common malformations that may occur in isolation or as a part of many syndromes. Accurate genetic diagnosis and counseling require detailed analysis of the external as well as the internal anatomy and knowledge of the relative frequencies of various malformations in syndromes that may have overlapping clinical signs. We have had the opportunity recently to study four cases of the Ritscher-Schinzel syndrome. A review of all reported cases is presented and an attempt made to define the minimum diagnostic criteria for the Ritscher-Schinzel syndrome. Of the nine craniofacial anomalies commonly reported as a part of the Ritscher-Schinzel syndrome, we consider two i.e., cleft palate and ocular coloboma, to be readily and objectively ascertainable. The other seven craniofacial traits, however, are somewhat subjective, require expert interpretation and are sometimes difficult to ascertain in a newborn or stillborn fetus. These are prominent forehead, prominent occiput, hypertelorism, down-slanting palpebral fissures, low-set ears, depressed nasal bridge and micrognathia. At least four of these were present in all cases that had a secure diagnosis of the Ritscher-Schinzel syndrome. Thus, the criteria we propose to establish the diagnosis of the Ritscher-Schinzel syndrome in a chromosomally normal sporadic case are the presence of cardiac malformation other than isolated patent ductus arteriosus, cerebellar malformation, and cleft palate or ocular coloboma or four of the following seven findings: prominent forehead, prominent occiput, hypertelorism, down-slanting palpebral fissures, low-set ears, depressed nasal bridge, and micrognathia.

Molecular determinants of the granulocyte-macrophage colony-stimulating factor receptor complex assembly

The granulocyte-macrophage colony-stimulating factor (GM-CSF) receptor (GMR) is composed of two chains that belong to the superfamily of cytokine receptors typified by the growth hormone receptor. A common structural element found in cytokine receptors is a module of two fibronectin-like domains, each characterized by seven beta-strands denoted A-G and A'-G', respectively. The alpha-chain (GMRalpha) confers low affinity GM-CSF binding (K(d) = 1-5 nM), whereas the beta-chain (beta(c)) does not bind GM-CSF by itself but confers high affinity binding when associated with alpha (K(d) = 40-100 pM). In the present study, we define the molecular determinants required for ligand recognition and for stabilization of the complex through a convergence of several approaches, including the construction of chimeric receptors, the molecular dynamics of our three-dimensional model of the GM.GMR complex, and site-directed mutagenesis. The functional importance of individual residues was then investigated through ligand binding studies at equilibrium and through determination of the kinetic constants of the GM.GMR complex. Critical to this tripartite complex is the establishment of four noncovalent bonds, three that determine the nature of the ligand recognition process involving residues Arg(280) and Tyr(226) of the alpha-chain and residue Tyr(365) of the beta-chain, since mutations of either one of these residues resulted in a significant decrease in the association rate. Finally, residue Tyr(365) of beta(c) serves a dual function in that it cooperates with another residue of beta(c), Tyr(421) to stabilize the complex since mutation of Tyr(365) and Tyr(421) result in a drastic increase in the dissociation rate (Koff). Interestingly, these four residues are located at the B'-C' and F'-G' loops of GMRalpha and of beta(c), thus establishing a functional symmetry within an apparently asymmetrical heterodimeric structure.

Serum erythropoietin levels and hematocrit in end-stage renal disease: influence of the mode of dialysis

Serum erythropoietin (Ep) levels were measured by radioimmunoassay in 70 patients with end-stage renal disease (ESRD) to evaluate the influence of the mode of dialysis on the relationship between serum Ep levels and the severity of anemia. Thirty-five patients were on hemodialysis (HD), seven were on intermittent peritoneal dialysis (IPD), and 28 were on continuous ambulatory peritoneal dialysis (CAPD). Compared to HD, CAPD patients had higher serum Ep (CAPD), 46.1 +/- 13.4 v HD, 16.9 +/- 2.2 mU/mL) and hematocrit (CAPD, 33.9 +/- 2.5 v HD, 24.8 +/- 1.4%; P less than 0.05). The Ep and Hct values for IPD patients were intermediate between the other two groups. Serum Ep levels were higher in CAPD patients in the first 4 weeks of initiation of CAPD (144 +/- 35 mU/mL, n = 6) than later (39 +/- 6.4 mU/mL, n = 24). A significant fluctuation in serum Ep and Hct values was noted in patients on all three modes of dialysis, when multiple samples were obtained at different time intervals. There was a weak correlation between serum Ep and Hct in the three groups of dialysis patients; r = 0.36, P less than 0.005. The data suggest that CAPD provides a better biochemical milieu for Ep production and responsiveness than HD treatment of ESRD.

The predominant lymphocyte in most thymomas and in nonneoplastic thymus from patients with myasthenia gravis is the cortical thymocyte

Cell suspensions prepared from 12 specimens of nonneoplastic thymus (6 normal and 6 from patients with myasthenia gravis) and from 17 thymomas were investigated with a panel of monoclonal antibodies. The great preponderance of thymocytes from the 12 nonneoplastic specimens and from 13 of the 17 thymomas (2 of 3 predominantly lymphocytic tumors and 11 of 12 mixed tumors) displayed the surface phenotype of cortical or common thymocytes. These cells formed rosettes with unsensitized sheep erythrocytes (E-rosettes) at both 4 and 37 degrees C, and reacted with the following monoclonal antibodies: OKT1 (thymic and peripheral T cells), OKT6 (common thymocytes), OKT10 (replicating lymphoid cells), OKT11 (sheep cell receptor), and both OKT4 (inducer-helper T cells) and OKT8 (cytotoxic-suppressor T cells). Few B cells (lymphocytes with either immunoglobulin or Ia-like antigen on the cell surface), and few cells with receptors for transferrin and interleukin 2 were detected. Thymocytes from 3 of the 4 remaining thymomas (2 predominantly epithelial tumors and 1 mixed tumor) displayed surface marker characteristics of medullary thymocytes or peripheral T cells; i.e., they were reactive with OKT1, OKT3 (peripheral T cells), OKT11, and either OKT4 or OKT8, and were also E-rosette positive only at 4 degrees C and TdT negative. Thymocytes from the final tumor, a lymphocytic thymoma, exhibited an intermediate phenotype. Thus, almost all mixed (11 of 12) and lymphocytic (2 of 3) thymomas were composed predominantly of cortical thymocytes, while the medullary cell was the rule in the two tumors that were predominantly epithelial.

Lymphocyte receptors for concanavalin A in Hodgkin disease

The number of lymphocytes with mobile receptors for concanavalin A (Con A) on their surface membrane (forming visible caps after the addition of fluorescein-conjugated Con A) was determined in the peripheral blood of 53 patients with Hodgkin disease. Of 29 individuals studied prior to treatment, the level of capped cells was found to be below the normal range in 9 of 13 in stages I and IIA, 6 of 8 in stage IIIA, and all 8 in stages IIIB and IV. Even among patients in remission 2 yr after successful treatment the level was below the lower normal limit in 9 of 16. The number was also reduced in 7 of 8 individuals with recurrent lymphoma. The level of lymphocytes that cap with Con A may prove to be a more sensitive measure of active Hodgkin disease than the total peripheral lymphocyte count or the level of T cells. This lymphocyte parameter merits further study as a correlate in vitro of cellular immunity.

Lymphosarcoma cell leukemia: the contribution of cell surface study to diagnosis

Cell surface immunoglobulin, complement receptor, and spontaneous rosette formation with sheep erythrocytes were investigated in 43 patients with malignant lymphoma, including 13 with lymphosarcoma cell leukemia, and in 59 patients with chronic lymphocytic leukemia. The quantity of immunoglobulin on the lymphocyte surface was estimated from the intensity of fluorescent staining with fluorescein-conjugated anti-immunoglobulin antisera. At least two, and probably three, B cell species could be recognized by cell surface study. Cells from chronic lymphocytic leukemia and diffuse well-differentiated lymphocytic lymphoma had sparse amounts of surface immunoglobulin, while the cells of diffuse poorly differentiated lymphocytic lymphoma had large quantities of this material. Nodular lymphoma probably represented a third B-cell subtype with intermediate amounts of surface immunoglobulin. The lymphocytes of chronic lymphosarcoma cell leukemia exhibited the intense surface staining, which was characteristic of the underlying poorly differentiated lymphocytic lymphoma (diffuse or nodular), and could be readily distinguished from the faint-staining chronic lymphocytic leukemia cells.