The formation of Charon's red poles from seasonally cold-trapped volatiles.

A unique feature of Pluto's large satellite Charon is its dark red northern polar cap. Similar colours on Pluto's surface have been attributed to tholin-like organic macromolecules produced by energetic radiation processing of hydrocarbons. The polar location on Charon implicates the temperature extremes that result from Charon's high obliquity and long seasons in the production of this material. The escape of Pluto's atmosphere provides a potential feedstock for a complex chemistry. Gas from Pluto that is transiently cold-trapped and processed at Charon's winter pole was proposed as an explanation for the dark coloration on the basis of an image of Charon's northern hemisphere, but not modelled quantitatively. Here we report images of the southern hemisphere illuminated by Pluto-shine and also images taken during the approach phase that show the northern polar cap over a range of longitudes. We model the surface thermal environment on Charon and the supply and temporary cold-trapping of material escaping from Pluto, as well as the photolytic processing of this material into more complex and less volatile molecules while cold-trapped. The model results are consistent with the proposed mechanism for producing the observed colour pattern on Charon.

The solar nebula origin of (486958) Arrokoth, a primordial contact binary in the Kuiper Belt.

The New Horizons spacecraft's encounter with the cold classical Kuiper Belt object (486958) Arrokoth (provisional designation 2014 MU69) revealed a contact-binary planetesimal. We investigated how Arrokoth formed and found that it is the product of a gentle, low-speed merger in the early Solar System. Its two lenticular lobes suggest low-velocity accumulation of numerous smaller planetesimals within a gravitationally collapsing cloud of solid particles. The geometric alignment of the lobes indicates that they were a co-orbiting binary that experienced angular momentum loss and subsequent merger, possibly because of dynamical friction and collisions within the cloud or later gas drag. Arrokoth's contact-binary shape was preserved by the benign dynamical and collisional environment of the cold classical Kuiper Belt and therefore informs the accretion processes that operated in the early Solar System.

Color, composition, and thermal environment of Kuiper Belt object (486958) Arrokoth.

The outer Solar System object (486958) Arrokoth (provisional designation 2014 MU69) has been largely undisturbed since its formation. We studied its surface composition using data collected by the New Horizons spacecraft. Methanol ice is present along with organic material, which may have formed through irradiation of simple molecules. Water ice was not detected. This composition indicates hydrogenation of carbon monoxide-rich ice and/or energetic processing of methane condensed on water ice grains in the cold, outer edge of the early Solar System. There are only small regional variations in color and spectra across the surface, which suggests that Arrokoth formed from a homogeneous or well-mixed reservoir of solids. Microwave thermal emission from the winter night side is consistent with a mean brightness temperature of 29 ± 5 kelvin.

The geology and geophysics of Kuiper Belt object (486958) Arrokoth.

The Cold Classical Kuiper Belt, a class of small bodies in undisturbed orbits beyond Neptune, is composed of primitive objects preserving information about Solar System formation. In January 2019, the New Horizons spacecraft flew past one of these objects, the 36-kilometer-long contact binary (486958) Arrokoth (provisional designation 2014 MU69). Images from the flyby show that Arrokoth has no detectable rings, and no satellites (larger than 180 meters in diameter) within a radius of 8000 kilometers. Arrokoth has a lightly cratered, smooth surface with complex geological features, unlike those on previously visited Solar System bodies. The density of impact craters indicates the surface dates from the formation of the Solar System. The two lobes of the contact binary have closely aligned poles and equators, constraining their accretion mechanism.

The geology of Pluto and Charon through the eyes of New Horizons.

NASA's New Horizons spacecraft has revealed the complex geology of Pluto and Charon. Pluto's encounter hemisphere shows ongoing surface geological activity centered on a vast basin containing a thick layer of volatile ices that appears to be involved in convection and advection, with a crater retention age no greater than ~10 million years. Surrounding terrains show active glacial flow, apparent transport and rotation of large buoyant water-ice crustal blocks, and pitting, the latter likely caused by sublimation erosion and/or collapse. More enigmatic features include tall mounds with central depressions that are conceivably cryovolcanic and ridges with complex bladed textures. Pluto also has ancient cratered terrains up to ~4 billion years old that are extensionally faulted and extensively mantled and perhaps eroded by glacial or other processes. Charon does not appear to be currently active, but experienced major extensional tectonism and resurfacing (probably cryovolcanic) nearly 4 billion years ago. Impact crater populations on Pluto and Charon are not consistent with the steepest impactor size-frequency distributions proposed for the Kuiper belt.

The small satellites of Pluto as observed by New Horizons.

The New Horizons mission has provided resolved measurements of Pluto's moons Styx, Nix, Kerberos, and Hydra. All four are small, with equivalent spherical diameters of ~40 kilometers for Nix and Hydra and ~10 kilometers for Styx and Kerberos. They are also highly elongated, with maximum to minimum axis ratios of ~2. All four moons have high albedos (~50 to 90%) suggestive of a water-ice surface composition. Crater densities on Nix and Hydra imply surface ages of at least 4 billion years. The small moons rotate much faster than synchronous, with rotational poles clustered nearly orthogonal to the common pole directions of Pluto and Charon. These results reinforce the hypothesis that the small moons formed in the aftermath of a collision that produced the Pluto-Charon binary.

Calcium transport by basal lateral membrane vesicles from rat small intestine decreases with age.

There is a marked decrease in active Ca2+ transport by the rat small intestine with age, particularly between 2 and 12 months. Much evidence suggests that the active component of Ca2+ transport resides in the energy-dependent pumping of Ca2+ across the intestinal basal lateral membrane. Therefore, we have characterized Ca2+ uptake by basal lateral membrane vesicles isolated from young (2-3 month old) and adult (12-14 month old) rats. In vesicles from the proximal duodenum, ATP-dependent Ca2+ uptake was about 4-times greater in the young animal than in the adult. There were no age differences in Ca2+ uptake in the absence of ATP. In vesicles from the ileum, Ca2+ uptake was much less than in the duodenum. The age differences in the ileum were smaller, and ATP-dependent Ca2+ uptake in the young was only twice that seen in the adult. Osmotic lysis of duodenal vesicles reduced Ca2+ uptake to low levels in both age groups, indicating that most of the Ca2+ was being taken up into an osmotically active space. Kinetic studies of Ca2+ uptake showed that there was no change in the apparent affinity but a 5-fold decrease in the Vmax of the adult Ca2+ transport system compared to that of the young animal. This marked decrease in the capacity of basal lateral membrane vesicles to actively transport Ca2+ may contribute to the decline in intestinal Ca2+ absorption with age.

Localization of cellular retinol-binding protein and cellular retinoic acid-binding protein in the rat testis and epididymis.

The distribution of cellular retinol-binding protein (CRBP) and cellular retinoic acid-binding protein (CRABP) in rat testis and epididymis was examined by the peroxidase-antiperoxidase immunolocalization technique. In the testis, cellular retinol-binding protein was localized exclusively in the Sertoli cells. Staining varied with the stages of the seminiferous epithelium cycle and was maximal prior to the maturation divisions. Cellular retinoic acid-binding protein was localized exclusively in the germinal cells in the adluminal compartment. The results suggest that retinoic acid may be the retinoid form used by the germinal cells, and that Sertoli cells may use the cellular retinol-binding protein to transfer retinol from the basal to the adluminal compartment. In the epididymis, cellular retinol-binding protein was localized in the cytoplasm and stereocilia of the principal cells in the proximal caput epididymidis, while cellular retinoic acid-binding protein was localized in the spermatozoa and the stereocilia of the principal cells throughout the epididymis and in the epithelial cells of the distal vas deferens. Sperm staining intensity decreased from the initial segment to the cauda. The presence of high levels of cellular retinol-binding protein in the epithelial cells and high levels of cellular retinoic acid-binding protein in the spermatozoa of the caput epididymidis, known to be involved in the synthesis and secretion of factors necessary for sperm maturation, suggests that vitamin A may have a role in this process.

Effect of inv mutations on Salmonella virulence and colonization in 1-day-old White Leghorn chicks.

Invasion of Salmonella into the cells of the intestinal epithelium is an important step in the infection process. This initial invasion is followed by colonization of other organs throughout the body. In an attempt to better understand this process, we moved defined mutations in several genes of the inv locus into Salmonella typhimurium UK-1 and two strains of Salmonella enteritidis. These mutant strains were evaluated for their oral and intraperitoneal virulence as determined by 50% lethal dose in 1-day-old white leghorn chicks. These inv mutants were also studied for their ability to colonize orally infected chicks. The invA, invB, and invC mutations all caused a reduction in oral virulence and colonization by UK-1 and the S. enteritidis strains. Mutation of the invH gene had little or no effect on oral virulence or colonization. None of the inv genes tested had any effect on virulence of these Salmonella strains when administered intraperitoneally.

Virulence of Salmonella typhimurium mutants for White Leghorn chicks.

A strain of Salmonella typhimurium that is highly virulent for 1-day-old white leghorn chicks was genetically modified by deletion (delta) of the adenylate cyclase (cya) and cyclic AMP receptor protein (crp) genes or by removal (curing) of the 91-kilobase virulence plasmid. These mutants were then compared with the wild-type S. typhimurium strain for virulence in 1-day-old chicks and for their ability to colonize chicks of various ages. The plasmid-cured mutant showed a slight reduction in virulence, whereas the delta cya delta crp mutant was completely avirulent. The wild-type strain and both mutant strains were capable of colonizing various organs within the chicks. At all time points, the delta cya delta crp strain colonized chicks at lower levels than the wild-type strain. Titers of the plasmid-cured strain increased more slowly in visceral organs than did those of the wild type.

Effect of infective dose on humoral immune responses and colonization in chickens experimentally infected with Salmonella typhimurium.

The influence of infective dose on chicken immunogenicity was examined in 1-week-old chickens. Chickens were infected orally with various doses of chi 3761 or chi 3985. Fecal shedding, colonization of the cecum, and induction of Salmonella-specific serum immunoglobulin isotypes were analyzed over a 5-week period. The delta cya delta crp Salmonella typhimurium vaccine strain chi 3985 was used to assess the effect of vaccination dose on protection after oral vaccination of chickens at 1 day and 2 weeks of age. Wild-type S. typhimurium strain chi 3761 was used to challenge vaccinated and unvaccinated chickens at 6 weeks of age, and the recovery of Salmonella from the cecum was used as a measure of protection. Infection of 1-week-old chickens with chi 3985 was more effective in reducing fecal excretion and cecal colonization than was infection with chi 3761. Double vaccination with 10(8) or 10(7) CFU of chi 3985 at 1 day and 2 weeks of age protected vaccinated chickens against cecal colonization by the challenge strain chi 3761. Immunogenicity of Salmonella is dose and genotype-dependent.

Vitamin A status affects chromatin structure.

We have examined RNA synthesis by nuclei isolated from testes of rats of varying vitamin A status. Nuclei from retinol-deficient animals showed substantially decreased RNA synthesis by polymerase II when compared to nuclei from normal animals. Within 4 hours after oral administration of retinyl acetate (as the source of retinol) to deficient animals, RNA synthesis by polymerase II had significantly increased. Administration of retinoic acid had a similar but lesser effect. Nucleoside analysis after alkaline hydrolysis of the RNA synthesized by the endogenous polymerase II suggested that the increased activity was due to a greater number of actively transcribing polymerase II molecules on the DNA. Further, when the template capacity of testicular chromatin isolated from deficient and retinyl acetate refed animals was compared, the number of sites recognized by E. coli RNA polymerase was increased twofold after retinyl acetate administration. We conclude that these retinol-induced changes in transcription are due at least in part to changes in chromatin structure.

Public knowledge and attitudes about AIDS among adults in Calcutta, India.

Despite the relatively recent introduction of human immunodeficiency virus (HIV) into India, the acquired immunodeficiency syndrome (AIDS) is rapidly becoming a significant health problem in that country. Education about AIDS remains the most effective strategy to prevent its spread. To assess the level of knowledge and the associated attitudes about AIDS among Indians in Calcutta, 153 English-speaking adults were surveyed during April and May 1990. Sixty-five of 75 men (87%) and 77 of 78 women (99%) questioned had heard of AIDS, the majority within the past 2-3 years. Newspaper and television were the most frequently cited sources of information. Of respondents who had heard of the disease, 95% knew AIDS was transmitted by sexual intercourse; less than half, however, also knew that AIDS could not be acquired through kissing, insect bites or by using public toilets. In general, respondents had little specific knowledge regarding the symptoms of AIDS, and 29% were unaware that infected persons could be asymptomatic and appear healthy. Level of education was the only variable that independently correlated with knowledge of AIDS. More than one-third of respondents would not have dinner with or continue to work with an AIDS patient and 50% believed all AIDS patients should be quarantined. More effective and widespread public education is necessary to help slow the rapidly developing AIDS epidemic in India.

Toxoplasmosis of the central nervous system in the acquired immunodeficiency syndrome.

BACKGROUND AND METHODS: Toxoplasmosis is the most common opportunistic infection of the central nervous system in patients with the acquired immunodeficiency syndrome (AIDS). To investigate its clinical course, we reviewed the records of 115 patients with AIDS and central nervous system toxoplasmosis treated at San Francisco General Hospital between 1981 and 1990. RESULTS: The most common presenting symptoms were headache (in 55 percent), confusion (52 percent), and fever (47 percent). Focal neurologic deficits were present in 79 patients (69 percent). The median CD4 cell count at presentation was 50 per cubic millimeter (50 x 10(6) per liter). Thirteen of 80 patients with clinical toxoplasmosis (16 percent) and 4 of 18 patients with pathologically proved disease (22 percent) had undetectable antitoxoplasma IgG antibodies by indirect immunofluorescence assay. Of 103 patients, 94 (91 percent) had enhancing lesions on CT. Single lesions were seen in 28 of 103 patients (27 percent) on CT, and such lesions were seen in 3 of 21 patients (14 percent) on magnetic resonance imaging. Over 90 percent of patients who eventually had clinical and radiographic improvement had evidence of improvement by day 14 of therapy. Adverse drug reactions occurred in 71 patients (62 percent) and led to a change in therapy in 50 patients (43 percent). Among the patients who survived a first episode of toxoplasmosis, the median survival was 265 days. CONCLUSIONS: Toxoplasmosis occurs in advanced stages of human immunodeficiency virus infection, and the absence of antitoxoplasma antibodies on immunofluorescence assay does not exclude the diagnosis. The clinical and radiographic response to therapy is usually rapid, but treatment is frequently limited by adverse drug effects.

Pseudotumor of infancy and congenital muscular torticollis.

Pseudotumor of infancy presents as a discrete, firm mass in the distal sternocleidomastoid muscle in infants two to four weeks of age. Congenital muscular torticollis may develop from the resultant fibrosis in 10 to 20 percent of cases. Hip dysplasia is an associated feature of congenital muscular torticollis in approximately 10 percent of cases. Pseudotumor of infancy must be differentiated from other causes of cervical soft tissue masses. Diagnostic choices include fine-needle aspiration biopsy, cervical radiography, ultrasonography, computed tomographic scanning of the head and neck, and magnetic resonance imaging. Left untreated, congenital muscular torticollis may lead to significant craniofacial asymmetry and scoliosis. Heat, massage and passive stretching exercises are the preferred initial treatments for pseudotumor and torticollis. More than 70 percent of patients will respond to this approach. Surgery should be reserved for treatment of cases that persist past the first year of life.

Erythropoiesis and vasculogenesis in embryoid bodies lacking visceral yolk sac endoderm.

During mouse embryogenesis the first hematopoietic and endothelial cells form in blood islands located between layers of visceral endoderm and mesoderm in the yolk sac. The role of visceral endoderm in primitive hematopoiesis and vasculogenesis is not well understood. We have assessed the consequences of a lack of visceral endoderm on blood cell and vessel formation using embryoid bodies derived from mouse embryonic stem (ES) cells deficient in GATA-4, a transcription factor expressed in yolk sac endoderm. When differentiated in vitro, these mutant embryoid bodies do not develop an external visceral endoderm layer. We found that Gata4-/- embryoid bodies, grown either in suspension culture or attached to a substratum, are defective in primitive hematopoiesis and vasculogenesis as evidenced by a lack of recognizable blood islands and vascular channels and a reduction in the expression of the primitive erythrocyte marker epsilon y-globin. Expression of the endothelial cell transcripts FIk-1, FIt-1, and platelet-endothelial cell adhesion molecule (PECAM) was not affected in the mutant embryoid bodies. Gata4-/- ES cells retained the capacity to differentiate into primitive erythroblasts and endothelial cells when cultured in methylcellulose or matrigel. Analysis of chimeric mice, generated by injecting Gata4-/- ES cells into 8-cell stage embryos of ROSA26 transgenic animals, showed that Gata4-/- ES cells can form blood islands and vessels when juxtaposed to visceral endoderm in vivo. We conclude that the visceral endoderm is not essential for the differentiation of primitive erythrocytes or endothelial cells, but this cell layer plays an important role in the formation and organization of yolk sac blood islands and vessels.

Localization of cellular retinol-binding protein in several rat tissues.

The distribution of cellular retinol-binding protein (CRBP) in rat liver, ileum, and epididymis was examined by the peroxidase-antiperoxidase immunolocalization technique. Positive cytoplasmic staining was seen in the liver when antiserum prepared against purified CRBP was used but not when antiserum absorbed with purified CRBP was used. Ileal mucosa, a tissue that contains no detectable CRBP, showed no positive staining. The epididymis showed strong positive staining in the caput but not in the cauda. Staining was present in principal and basal cells but not in peritubular or interstitial cells. Radioimmunoassay revealed that the CRBP within the caput epididymidis was localized in the initial segment and proximal region, areas known to be involved in the synthesis and secretion of factors necessary for sperm maturation. The results demonstrate that the expression of CRBP may vary within the same cell type, as well as between different cell types within the same tissue.