Attraction of the parasitic mite varroa to the drone larvae of honey bees by simple aliphatic esters

An important parasitic threat to honey bees, the mite Varroa jacobsoni, is attracted to its major prey, drone larvae, by methyl and ethyl esters of straight-chain fatty acids, in particular methyl palmitate. These esters were extracted from drone larvae with n-hexane and were identified by gas chromatography-mass spectrometry. Their behavioral effect was evaluated with the use of a four-arm airflow olfactometer.     

Communication of direction by the honey bee

In the presence of controls for site- and path-specific odors, observer and food-source scents, Nasanov gland and alarm odors, visual cues, wind, and general site taxis, recruited bees were able to locate the food source indicated by the dances of returning foragers in preference to a food source located at an equal distance in the opposite direction. This was true even when foragers were simultaneously dancing to indicate two different stations. Recruitment in the absence of dancing was very low, while in the absence of foraging it was virtually zero. Thus, under the experimental conditions used, the directional information contained in the dance appears to have been communicated from forager to recruit and subsequently used by the recruit.     

Identification of the honey bee swarming process by analysing the time course of hive vibrations

Honey bees live in groups of approximately 40,000 individuals and go through their reproductive cycle by the swarming process, during which the old queen leaves the nest with numerous workers and drones to form a new colony. In the spring time, many clues can be seen in the hive, which sometimes demonstrate the proximity to swarming, such as the presence of more or less mature queen cells. In spite of this the actual date and time of swarming cannot be predicted accurately, as we still need to better understand this important physiological event. Here we show that, by means of a simple transducer secured to the outside wall of a hive, a set of statistically independent instantaneous vibration signals of honey bees can be identified and monitored in time using a fully automated and non-invasive method. The amplitudes of the independent signals form a multi-dimensional time-varying vector which was logged continuously for eight months. We found that combined with specifically tailored weighting factors, this vector provides a signature highly specific to the swarming process and its build up in time, thereby shedding new light on it and allowing its prediction several days in advance. The output of our monitoring method could be used to provide other signatures highly specific to other physiological processes in honey bees, and applied to better understand health issues recently encountered by pollinators.     

Vertical distribution of an estuarine snail altered by a parasite

Estuarine snails Ilyanassa obsoleta bearing larvae of the trematode Gynaecotyla adunca behave singularly in comparison with conspecifics lacking this parasite. Following high tides, and especially at night, infected snails were found stranded high on beaches and sandbars. Semiterrestrial crustaceans living well up on the shore serve as the next host, and the modified (induced) snail behavior is apparently a parasite adaptation facilitating cercarial transmission to these crustaceans. The altered behavior is unusual because of its apparent enhancement of host-to-host transmission by cercariae rather than predation, the process commonly recognized as being enhanced by parasitic modification of host behavior.     

Host immune system gene targeting by a viral miRNA

Virally encoded microRNAs (miRNAs) have recently been discovered in herpesviruses. However, their biological roles are mostly unknown. We developed an algorithm for the prediction of miRNA targets and applied it to human cytomegalovirus miRNAs, resulting in the identification of the major histocompatibility complex class I-related chain B (MICB) gene as a top candidate target of hcmv-miR-UL112. MICB is a stress-induced ligand of the natural killer (NK) cell activating receptor NKG2D and is critical for the NK cell killing of virus-infected cells and tumor cells. We show that hcmv-miR-UL112 specifically down-regulates MICB expression during viral infection, leading to decreased binding of NKG2D and reduced killing by NK cells. Our results reveal a miRNA-based immunoevasion mechanism that appears to be exploited by human cytomegalovirus.     

Mechanically induced wall appositions of plant cells can prevent penetration by a parasitic fungus

Localized, paramural wall appositions resembling appositions commonly induced by fungal attack, were induced in kohlrabi (Brassica oleracea L. gongyloides) by mechanical wounding (bending) of the root hairs before the hairs were inoculated with zoospores of a compatible parasitic fungus. The appositions were effective in preventing fungal penetration at the wound sites, which shows that wall appositions can prevent fungal ingress into plant cells.     

T-cell recognition of Ia molecules selectively altered by a single amino acid substitution

T lymphocytes recognize foreign antigen together with allele-specific determinants on membrane-bound class I and class II (Ia) gene products of the major histocompatibility complex. To identify amino acids of class II molecules critical to this recognition process, the genes encoding the beta chains of the I-Ak molecule were cloned from a wild-type B-cell hybridoma and from an immunoselected variant subline showing distinct serological and T-cell stimulatory properties. Nucleotide sequencing and DNA-mediated gene transfer established that a single base transition (G----A) encoding a change from glutamic acid to lysine at position 67 in the I-Ak beta molecule accounted for all the observed phenotypic changes of the variant cells. These results confirm the importance of residues 62 to 78 in the amino terminal domain of I-A beta for class II-restricted T-cell recognition of antigen and demonstrate the ability of a single substitution in this region to alter this recognition event.     

Ubiquitination on nonlysine residues by a viral E3 ubiquitin ligase

Ubiquitination controls a broad range of cellular functions. The last step of the ubiquitination pathway is regulated by enzyme type 3 (E3) ubiquitin ligases. E3 enzymes are responsible for substrate specificity and catalyze the formation of an isopeptide bond between a lysine residue of the substrate (or the N terminus of the substrate) and ubiquitin. MIR1 and MIR2 are two E3 ubiquitin ligases encoded by Kaposi's sarcoma-associated herpesvirus that mediate the ubiquitination of major histocompatibility complex class I (MHC I) molecules and subsequent internalization. Here, we found that MIR1, but not MIR2, promoted down-regulation of MHC I molecules lacking lysine residues in their intracytoplasmic domain. In the presence of MIR1, these MHC I molecules were ubiquitinated, and their association with ubiquitin was sensitive to beta2-mercaptoethanol, unlike lysine-ubiquitin bonds. This form of ubiquitination required a cysteine residue in the intracytoplasmic tail of MHC I molecules. An MHC I molecule containing a single cysteine residue in an artificial glycine and alanine intracytoplasmic domain was endocytosed and degraded in the presence of MIR1. Thus, ubiquitination can occur on proteins lacking accessible lysines or an accessible N terminus.     

Induction of mesoderm by a viral oncogene in early Xenopus embryos

During frog embryogenesis, mesoderm is specified in the equatorial region of the early embryo by a signal from the vegetal hemisphere. Prospective ectodermal cells dissected from the animal hemisphere can be respecified to form mesodermal tissues by recombination with vegetal tissue or by treatment with any of several polypeptide growth factors or growth factor-like molecules. Together with the discovery that several developmental mutations in Drosophila are in genes with significant homology to mammalian mitogens and oncogenes, these observations suggest that early developmental signals may use similar transduction pathways to mitogenic signals characterized in cultured mammalian cells. Whether mesoderm can be induced by activation of intracellular signal transduction pathways implicated in mitogenesis and oncogenesis has been investigated with the viral oncogene polyoma middle T. Microinjection of middle T messenger RNA into early embryos results in the respecification of isolated prospective ectodermal tissue to form characteristic mesodermal structures. Middle T in frog blastomeres appears to associate with cellular activities similar to those observed in polyoma-transformed mouse cells, and transformation-defective middle T mutants fail to induce mesoderm. These results suggest that early inductive signals and mitogenic and oncogenic stimuli may share common signal transduction pathways.     

Structural basis for ribosome recruitment and manipulation by a viral IRES RNA

Canonical cap-dependent translation initiation requires a large number of protein factors that act in a stepwise assembly process. In contrast, internal ribosomal entry sites (IRESs) are cis-acting RNAs that in some cases completely supplant these factors by recruiting and activating the ribosome using a single structured RNA. Here we present the crystal structures of the ribosome-binding domain from a Dicistroviridae intergenic region IRES at 3.1 angstrom resolution, providing a view of the prefolded architecture of an all-RNA translation initiation apparatus. Docking of the structure into cryo-electron microscopy reconstructions of an IRES-ribosome complex suggests a model for ribosome manipulation by a dynamic IRES RNA.     

Enhanced activity and altered specificity of phospholipase A2 by deletion of a surface loop

Protein engineering and x-ray crystallography have been used to study the role of a surface loop that is present in pancreatic phospholipases but is absent in snake venom phospholipases. Removal of residues 62 to 66 from porcine pancreatic phospholipase A2 does not change the binding constant for micelles significantly, but it improves catalytic activity up to 16 times on micellar (zwitterionic) lecithin substrates. In contrast, the decrease in activity on negatively charged substrates is greater than fourfold. A crystallographic study of the mutant enzyme shows that the region of the deletion has a well-defined structure that differs from the structure of the wild-type enzyme. No structural changes in the active site of the enzyme were detected.     

Orientation of homing pigeons altered by a change in the direction of an applied magnetic field

Homing pigeons were equipped with a pair of small coils around their heads. Birds with an induced field of 0.6 gauss and the south magnetic pole up, oriented toward home normally under both sun and overcast. Birds with the polarity reversed oriented toward home when the sun was visible but often flew away from home under overcast.     

Global cooling after the eruption of Mount Pinatubo: a test of climate feedback by water vapor

The sensitivity of Earth's climate to an external radiative forcing depends critically on the response of water vapor. We use the global cooling and drying of the atmosphere that was observed after the eruption of Mount Pinatubo to test model predictions of the climate feedback from water vapor. Here, we first highlight the success of the model in reproducing the observed drying after the volcanic eruption. Then, by comparing model simulations with and without water vapor feedback, we demonstrate the importance of the atmospheric drying in amplifying the temperature change and show that, without the strong positive feedback from water vapor, the model is unable to reproduce the observed cooling. These results provide quantitative evidence of the reliability of water vapor feedback in current climate models, which is crucial to their use for global warming projections.     

Binding of HTLV-III/LAV to T4+ T cells by a complex of the 110K viral protein and the T4 molecule

Human T-lymphotropic virus type III (HTLV-III) or lymphadenopathy-associated virus (LAV) is tropic for human T cells with the helper-inducer phenotype, as defined by reactivity with monoclonal antibodies specific for the T4 molecule. Treatment of T4+ T cells with monoclonal antibodies to T4 antigen blocks HTLV-III/LAV binding, syncytia formation, and infectivity. Thus, it has been inferred that the T4 molecule itself is a virus receptor. In the present studies, the surfaces of T4+ T cells were labeled radioactively, and then the cells were exposed to virus. After the cells were lysed, HTLV-III/LAV antibodies were found to precipitate a surface protein with a molecular weight of 58,000 (58K). By blocking and absorption experiments, this 58K protein was identified as the T4 molecule. No cell-surface structures other than the T4 molecule were involved in the antibody-antigen complex formation. Two monoclonal antibodies, each reactive with a separate epitope of the T4 molecule, were tested for their binding capacities in the presence of HTLV-III/LAV. When HTLV-III/LAV was bound to T4+ T cells, the virus blocked the binding of one of the monoclonal antibodies, T4A (OKT4A), but not of the other, T4 (OKT4). When HTLV-III/LAV was internally radiolabeled and bound to T4+ T cells which were then lysed, a viral glycoprotein of 110K (gp110) coprecipitated with the T4 molecule. The binding of gp110 to the T4 molecule may thus be a major factor in HTLV-III/LAV tropism and may prove useful in developing therapeutic or preventive measures for the acquired immune deficiency syndrome.     

土地利用转型影响下大别山区景观格局演变及驱动力研究

城镇化的迅猛发展导致了土地利用形态与功能的转型,而这一转变在山区尤为明显。同时景观格局的变化是土地利用转型的突出标志,探究两者的关系对于山区土地利用及生态管理具有重要意义。以地处大别山区的安徽省六安市金寨县为研究对象,选取1999年、2009年和2019年3期遥感卫星影像数据,在遥感与地理信息系统的技术支持下,采用土地利用转移矩阵、景观格局指数对金寨县的景观格局演变特征进行定量分析,并利用主成分分析法研究金寨县景观格局演变的驱动力。研究结果显示:(1)1999―2019年,金寨县土地利用转型特征为生产用地向生活用地和生态用地转换,建设用地转换率最高,持续增长,耕地和未利用地面积呈降低趋势,林地和水域持续稳定增长;土地利用类型上,主要为耕地、建设用地、未利用地、林地之间的转换;土地利用空间上,1999―2009年金寨县土地利用转换主要集中在中部地区,2010―2019年主要集中在东北部;(2)金寨县景观格局整体上破碎度增大,景观异质性、均匀度降低,不规则斑块增多,2010―2019年各景观类型间断分布,景观连通性下降;(3)金寨县的经济发展、产业水平、人口情况、生活水平和治理环境五个维度...