July 2012 Greenland melt extent enhanced by low-level liquid clouds.

Melting of the world's major ice sheets can affect human and environmental conditions by contributing to sea-level rise. In July 2012, an historically rare period of extended surface melting was observed across almost the entire Greenland ice sheet, raising questions about the frequency and spatial extent of such events. Here we show that low-level clouds consisting of liquid water droplets ('liquid clouds'), via their radiative effects, played a key part in this melt event by increasing near-surface temperatures. We used a suite of surface-based observations, remote sensing data, and a surface energy-balance model. At the critical surface melt time, the clouds were optically thick enough and low enough to enhance the downwelling infrared flux at the surface. At the same time they were optically thin enough to allow sufficient solar radiation to penetrate through them and raise surface temperatures above the melting point. Outside this narrow range in cloud optical thickness, the radiative contribution to the surface energy budget would have been diminished, and the spatial extent of this melting event would have been smaller. We further show that these thin, low-level liquid clouds occur frequently, both over Greenland and across the Arctic, being present around 30-50 per cent of the time. Our results may help to explain the difficulties that global climate models have in simulating the Arctic surface energy budget, particularly as models tend to under-predict the formation of optically thin liquid clouds at supercooled temperatures--a process potentially necessary to account fully for temperature feedbacks in a warming Arctic climate.

Enhanced expression of mucin genes in a guinea pig model of allergic asthma.

The ovalbumin (OVA)-sensitized guinea pig is often used as an animal model of asthma and airway hyperreactivity. A characteristic lesion of asthma is excessive production of mucin in the airways. Mechanistic studies of this lesion in guinea pigs have been limited due to lack of mucin gene probes for this species. The aim of the present study was to clone the cDNAs encoding two major airway mucins (Muc2 and Muc5ac) from the guinea pig, and investigate mucin gene expression in lungs of sensitized animals in response to antigen challenge. We isolated and sequenced two cDNA fragments coding for the sequences located within the carboxyl-terminal cysteine-rich region of guinea pig Muc2 and Muc5ac mucins. Comparison of cloned cDNAs with those from other species revealed high degrees of sequence identity and conservation of all cysteine residues in deduced primary sequences. Based on the resultant sequence information, we also designed oligonucleotide primers for specific detection of guinea-pig Muc2 and Muc5ac steady-state mRNA levels via reverse transcriptase/ polymerase chain reaction (RT-PCR). Levels of both Muc2 and Muc5ac mRNA in lungs of OVA-sensitized guinea pigs increased significantly by 30 min after an acute exposure to 0.3% OVA. In addition, levels of eotaxin mRNA also increased in these tissues, but the increases were not significant until 2 h after challenge. Correspondingly, the number of eosinophils in bronchoalveolar lavage fluid did not increase until 4 h postchallenge. Results of these studies suggest that the OVA-sensitized guinea pig responds to allergic challenge with enhanced expression of genes (e.g., eotaxin, Muc2, and Muc5ac) that likely play a role in increased airway inflammation and mucin overproduction, and enhanced mucin gene expression appears to occur before eosinophil infiltration.

Quantification and localization of N-acetyl-beta-D-hexosaminidase in the adult rat testis and epididymis.

An affinity-purified polyclonal antibody against N-acetyl-beta-D-hexosaminidase (EC 3.2.1.52) from adult rat epididymis was used to develop an ELISA, to localize tissue antigen by immunocytochemistry, and to identify isoforms of the enzyme by Western blot analysis. While peak activity level was measured in the corpus region of the epididymis, the quantity of soluble enzyme protein was highest in the caput region. Luminal caput sperm were intensely immunopositive, whereas epithelial cells were weakly stained. The enzyme was localized to epithelial and sperm cells of the corpus and caudal regions. In the testis, the enzyme was restricted primarily to lymphatic spaces. Testicular cells were unreactive, but spermatids were weakly stained. Western blot analysis revealed three prominent immune-reactive protein variants of approximately 63 kDa, approximately 55 kDa, and approximately 31 kDa. The approximately 31-kDa immune-reactive protein variant was reduced by > 84% in the caput epididymis compared to the cauda and corpus regions. These data suggest that regional differences in N-acetyl-beta-D-hexosaminidase activity in the rat epididymis may be due to differences in cellular synthesis and/or posttranslational processing of the enzyme.