Neuropeptide Y in the guinea-pig biliary tract

Summary High concentrations of neuropeptide Y (NPY) have been demonstrated in the gall bladder (16.7±5.4 pmol/g), cystic duct (25.4±9.2 pmol/g) and common bile duct (54.7±11.5 pmol/g) of the guinea-pig using a recently developed radio-immunoassay. Immunoreactive NPY containing nerves were demonstrated in all layers of the biliary tree using immunocytochemistry, being particularly dense in the myenteric and mucosal plexuses.Acknowledgments. JMA is a recipient of a Wellcome Trust Training Fellowship. JG is a visiting scholar from the Department of Pathology, Peking Medical College, Peking, China.     

Domain interactions of H-2 class I antigens alter cytotoxic T-cell recognition sites

H-2 class I antigens appear to direct the recognition of virus-infected and neoplastic transformed cells by cytotoxic T lymphocytes (CTLs). Here, to identify the regions of class I antigens involved in CTL recognition, four hybrid class I genes were constructed in which exons were exchanged between the H-2Kb and H-2Db genes. These class I genes were expressed in mouse L cells and recognition of the hybrid Kb/Db antigens by CTLs and monoclonal antibodies specific for either Kb or Db was investigated. The pattern of CTL and monoclonal antibody recognition obtained indicates three correlations between structure and function of class I antigens. First, most CTL recognition sites and alloantigenic determinants are located on domains 1 and 2 of the antigen molecule. Second, these CTL recognition sites and alloantigenic determinants are not influenced by interaction of domains 1 and 2 with polymorphic regions of domain 3. Third, in contrast, interaction between domains 1 and 2 alters these CTL recognition sites and alloantigenic determinants. The alteration of CTL recognition sites by interaction between domains 1 and 2 suggests that a CTL site may be formed by amino acids from both domains 1 and 2, or that the conformation of amino acids at a CTL site may be altered by interactions between domains 1 and 2. Through these two features, the conformation of CTL recognition sites on H-2 class I antigens may be sensitive to alteration by interaction of either domain 1 or 2 with viral antigens.     

Calcium channels activated by hydrogen peroxide mediate abscisic acid signalling in guard cells

Drought is a major threat to agricultural production. Plants synthesize the hormone abscisic acid (ABA) in response to drought, triggering a signalling cascade in guard cells that results in stomatal closure, thus reducing water loss. ABA triggers an increase in cytosolic calcium in guard cells ([Ca2+]cyt) that has been proposed to include Ca2+ influx across the plasma membrane. However, direct recordings of Ca2+ currents have been limited and the upstream activation mechanisms of plasma membrane Ca2+ channels remain unknown. Here we report activation of Ca2+-permeable channels in the plasma membrane of Arabidopsis guard cells by hydrogen peroxide. The H2O2-activated Ca2+ channels mediate both influx of Ca2+ in protoplasts and increases in [Ca2+]cyt in intact guard cells. ABA induces the production of H2O2 in guard cells. If H2O2 production is blocked, ABA-induced closure of stomata is inhibited. Moreover, activation of Ca2+ channels by H2O2 and ABA- and H2O2-induced stomatal closing are disrupted in the recessive ABA-insensitive mutant gca2. These data indicate that ABA-induced H2O2 production and the H2O2-activated Ca2+ channels are important mechanisms for ABA-induced stomatal closing.     

A map of the day-night contrast of the extrasolar planet HD 189733b

'Hot Jupiter' extrasolar planets are expected to be tidally locked because they are close (<0.05 astronomical units, where 1 au is the average Sun-Earth distance) to their parent stars, resulting in permanent daysides and nightsides. By observing systems where the planet and star periodically eclipse each other, several groups have been able to estimate the temperatures of the daysides of these planets. A key question is whether the atmosphere is able to transport the energy incident upon the dayside to the nightside, which will determine the temperature at different points on the planet's surface. Here we report observations of HD 189733, the closest of these eclipsing planetary systems, over half an orbital period, from which we can construct a 'map' of the distribution of temperatures. We detected the increase in brightness as the dayside of the planet rotated into view. We estimate a minimum brightness temperature of 973 +/- 33 K and a maximum brightness temperature of 1,212 +/- 11 K at a wavelength of 8 mum, indicating that energy from the irradiated dayside is efficiently redistributed throughout the atmosphere, in contrast to a recent claim for another hot Jupiter. Our data indicate that the peak hemisphere-integrated brightness occurs 16 +/- 6 degrees before opposition, corresponding to a hotspot shifted east of the substellar point. The secondary eclipse (when the planet moves behind the star) occurs 120 +/- 24 s later than predicted, which may indicate a slightly eccentric orbit.     

Control of leaf morphogenesis by microRNAs

Plants with altered microRNA metabolism have pleiotropic developmental defects, but direct evidence for microRNAs regulating specific aspects of plant morphogenesis has been lacking. In a genetic screen, we identified the JAW locus, which produces a microRNA that can guide messenger RNA cleavage of several TCP genes controlling leaf development. MicroRNA-guided cleavage of TCP4 mRNA is necessary to prevent aberrant activity of the TCP4 gene expressed from its native promoter. In addition, overexpression of wild-type and microRNA-resistant TCP variants demonstrates that mRNA cleavage is largely sufficient to restrict TCP function to its normal domain of activity. TCP genes with microRNA target sequences are found in a wide range of species, indicating that microRNA-mediated control of leaf morphogenesis is conserved in plants with very different leaf forms.     

Recent Northern Hemisphere tropical expansion primarily driven by black carbon and tropospheric ozone

Observational analyses have shown the width of the tropical belt increasing in recent decades as the world has warmed. This expansion is important because it is associated with shifts in large-scale atmospheric circulation and major climate zones. Although recent studies have attributed tropical expansion in the Southern Hemisphere to ozone depletion, the drivers of Northern Hemisphere expansion are not well known and the expansion has not so far been reproduced by climate models. Here we use a climate model with detailed aerosol physics to show that increases in heterogeneous warming agents--including black carbon aerosols and tropospheric ozone--are noticeably better than greenhouse gases at driving expansion, and can account for the observed summertime maximum in tropical expansion. Mechanistically, atmospheric heating from black carbon and tropospheric ozone has occurred at the mid-latitudes, generating a poleward shift of the tropospheric jet, thereby relocating the main division between tropical and temperate air masses. Although we still underestimate tropical expansion, the true aerosol forcing is poorly known and could also be underestimated. Thus, although the insensitivity of models needs further investigation, black carbon and tropospheric ozone, both of which are strongly influenced by human activities, are the most likely causes of observed Northern Hemisphere tropical expansion.