Ecological comparison of sympatric populations of sand lizards ( Cophosaurus texanus and Callisaurus draconoides )

Sympatric populations of Cophosaurus texanus and Callisaurus draconoides were periodically sampled from March 1973 through April 1974 at Burro Creek, Mohave County, Arizona. Callisaurus were also sampled at Rock Valley, Nye County, Nevada. Sex ratios were skewed in favor of males in the adult Cophosaurus but were equal in both adult populations of Callisaurus. Both species became sexually mature as yearlings. Mean clutch sizes were 3.55 (±0.83) for Cophosaurus, and 4.25 (±1.08) and 5.07 (±1.33) for Callisaurus at Burro Creek and Rock Valley respectively. Evidence of multiple clutches was exhibited by both species. Egg weight/body weight ratios for both species and clutch weight/body weight ratios for Cophosaurus were notably smaller than previously reported. At Burro Creek both species were highly insectivorus, with orthopterans comprising the largest food group of each. Niche overlap for food was high at the ordinal level, but at the familial level it is apparent that Callisaurus probably fed in the more xeric areas of the riparian habitat. No differences were found in the temperature responses of these two lizards. However, minor temporal separations and substantial spatial partitioning were observed. Callisaurus preferred sandy open areas, while Cophosaurus preferred the presence of some rocks and boulders.     

Mushroom consumption (mycophagy) by North American cervids

Native mushrooms play an important, though often underestimated, role in deer, elk, and caribou diets in North America. Mushrooms are often noted as an unusual or anomalous food in the diets of cervids; yet they often dominate diets in the late summer and fall in forested areas of western North America and throughout the year in the southeastern U.S. Mushrooms are particularly high in protein (16-19%), phosphorus (average 0.75%), and potassium (average 2%). Also, mushroom production is generally greatest in fall. Therefore, they are a highly nutritious food in late season when other native forages may marginally meet basal nutrient requirements of ungulates.     

HIV-1 superinfection despite broad CD8+ T-cell responses containing replication of the primary virus

Early treatment of acute HIV-1 infection followed by treatment interruptions has shown promise for enhancing immune control of infection. A subsequent loss of control, however, allows the correlates of protective immunity to be assessed. Here we show that sudden breakthrough of plasma viraemia occurred after prolonged immune containment in an individual infected with HIV-1 at a time when 25 distinct CD8+ T-cell epitopes in the viral proteins Gag, RT, Integrase, Env, Nef, Vpr, Vif and Rev were being targeted. Sequencing of the virus in plasma and cells showed that superinfection with a second clade-B virus was coincident with the loss of immune control. This sudden increase in viraemia was associated with a decline in half of the CD8+ T-cell responses. The declining CD8+ T-cell responses were coupled with sequence changes relative to the initial virus that resulted in impaired recognition. Our data show that HIV-1 superinfection can occur in the setting of a strong and broadly directed virus-specific CD8+ T-cell response. The lack of cross-protective immunity for closely related HIV-1 strains, despite persistent recognition of multiple CD8 epitopes, has important implications for public health and vaccine development.     

Mutations of the BRAF gene in human cancer

Cancers arise owing to the accumulation of mutations in critical genes that alter normal programmes of cell proliferation, differentiation and death. As the first stage of a systematic genome-wide screen for these genes, we have prioritized for analysis signalling pathways in which at least one gene is mutated in human cancer. The RAS RAF MEK ERK MAP kinase pathway mediates cellular responses to growth signals. RAS is mutated to an oncogenic form in about 15% of human cancer. The three RAF genes code for cytoplasmic serine/threonine kinases that are regulated by binding RAS. Here we report BRAF somatic missense mutations in 66% of malignant melanomas and at lower frequency in a wide range of human cancers. All mutations are within the kinase domain, with a single substitution (V599E) accounting for 80%. Mutated BRAF proteins have elevated kinase activity and are transforming in NIH3T3 cells. Furthermore, RAS function is not required for the growth of cancer cell lines with the V599E mutation. As BRAF is a serine/threonine kinase that is commonly activated by somatic point mutation in human cancer, it may provide new therapeutic opportunities in malignant melanoma.     

碳纳米管的革命

20世纪 90年代初 ,在日本NEC公司筑波实验室的一次偶然发现把世界带进了碳纳米管时代。今天 ,人们对碳纳米管的研究兴趣仍有增无减 ,本文作者就这 1 0年来的相关进展作一回顾——     

The transition to a sulphidic ocean approximately 1.84 billion years ago

The Proterozoic aeon (2.5 to 0.54 billion years (Gyr) ago) marks the time between the largely anoxic world of the Archean (> 2.5 Gyr ago) and the dominantly oxic world of the Phanerozoic (< 0.54 Gyr ago). The course of ocean chemistry through the Proterozoic has traditionally been explained by progressive oxygenation of the deep ocean in response to an increase in atmospheric oxygen around 2.3 Gyr ago. This postulated rise in the oxygen content of the ocean is in turn thought to have led to the oxidation of dissolved iron, Fe(II), thus ending the deposition of banded iron formations (BIF) around 1.8 Gyr ago. An alternative interpretation suggests that the increasing atmospheric oxygen levels enhanced sulphide weathering on land and the flux of sulphate to the oceans. This increased rates of sulphate reduction, resulting in Fe(II) removal in the form of pyrite as the oceans became sulphidic. Here we investigate sediments from the approximately 1.8-Gyr-old Animikie group, Canada, which were deposited during the final stages of the main global period of BIF deposition. This allows us to evaluate the two competing hypotheses for the termination of BIF deposition. We use iron-sulphur-carbon (Fe-S-C) systematics to demonstrate continued ocean anoxia after the final global deposition of BIF and show that a transition to sulphidic bottom waters was ultimately responsible for the termination of BIF deposition. Sulphidic conditions may have persisted until a second major rise in oxygen between 0.8 to 0.58 Gyr ago, possibly reducing global rates of primary production and arresting the pace of algal evolution.     

Tissue repair and stem cell renewal in carcinogenesis

Cancer is increasingly being viewed as a stem cell disease, both in its propagation by a minority of cells with stem-cell-like properties and in its possible derivation from normal tissue stem cells. But stem cell activity is tightly controlled, raising the question of how normal regulation might be subverted in carcinogenesis. The long-known association between cancer and chronic tissue injury, and the more recently appreciated roles of Hedgehog and Wnt signalling pathways in tissue regeneration, stem cell renewal and cancer growth together suggest that carcinogenesis proceeds by misappropriating homeostatic mechanisms that govern tissue repair and stem cell self-renewal.     

Dominant influence of HLA-B in mediating the potential co-evolution of HIV and HLA

The extreme polymorphism in the human leukocyte antigen (HLA) class I region of the human genome is suggested to provide an advantage in pathogen defence mediated by CD8+ T cells. HLA class I molecules present pathogen-derived peptides on the surface of infected cells for recognition by CD8+ T cells. However, the relative contributions of HLA-A and -B alleles have not been evaluated. We performed a comprehensive analysis of the class I restricted CD8+ T-cell responses against human immunodeficiency virus (HIV-1), immune control of which is dependent upon virus-specific CD8+ T-cell activity. In 375 HIV-1-infected study subjects from southern Africa, a significantly greater number of CD8+ T-cell responses are HLA-B-restricted, compared to HLA-A (2.5-fold; P = 0.0033). Here we show that variation in viral set-point, in absolute CD4 count and, by inference, in rate of disease progression in the cohort, is strongly associated with particular HLA-B but not HLA-A allele expression (P < 0.0001 and P = 0.91, respectively). Moreover, substantially greater selection pressure is imposed on HIV-1 by HLA-B alleles than by HLA-A (4.4-fold, P = 0.0003). These data indicate that the principal focus of HIV-specific activity is at the HLA-B locus. Furthermore, HLA-B gene frequencies in the population are those likely to be most influenced by HIV disease, consistent with the observation that B alleles evolve more rapidly than A alleles. The dominant involvement of HLA-B in influencing HIV disease outcome is of specific relevance to the direction of HIV research and to vaccine design.