Resource partitioning and interspecific interactions among sympatric rain forest arboreal mammals of the Western Ghats, India

Resource partitioning in a community of diurnal arboreal mammalsconsisting of the lion-tailed macaque Macaca silenus, bonnetmacaque (BM) Macaca radiata, Nilgiri langur Semnopithecus johnii,and the Indian giant squirrel Ratufa indica of the Western Ghats,southern India, was studied. Differences in their diet, verticalstratification, food resource niche breadth, niche overlap,and behavioral interactions were examined. Resource partitioningwas through differential habitat use, resource use, and verticalstratification. Of the four species, the BM was not a residentspecies and made frequent forays into evergreen forest fromthe adjacent deciduous forest during the flowering season ofCullenia exarillata and fruiting season of Ficus microcarpa.The macaques had narrower niches, and the langur and the squirrelhad wider niches. Niche overlap was highest between the twomacaques. Overlap among the study species was particularly pronouncedduring the flowering of C. exarillata. There was significantcorrelation between niche overlap and intolerance among thestudy species. Certain species pairs showed little or no mutualintolerance despite high overlap. Cooperative interactions suchas alarm calls occurred more frequently among the resident species.Interaction matrices revealed an underlying pattern of interspecificdominance hierarchy, with the BM dominating over the other threespecies. Our study suggests that the BM do not coexist withthe other three because of high overlap with its congener andlow occurrence of cooperative interactions.     

Characterization of microsatellite DNA markers in a critically endangered species,Mekong giant catfish,Pangasianodon gigas

Microsatellite DNA markers for a critically endangered Mekong giant catfish (Pangasianodon gigas Roberts and Vidthayanon, 1991) were developed from fin clips collected from captive fish using (GT)₁₅ probe. The number of alleles per locus ranged from two to four. The expected heterozygosities ranged from 0.13 to 0.68. Also, these primers were successfully amplified in four closely related species, Pangasius bocourti, Pangasius conchophilus, Pangasius larnaudii and Pangasius sanitwongsei with the number of alleles per locus ranged from 1 to 13, 1 to 16, 1 to 12 and 1 to 4, respectively. These markers should prove to be very useful for the evaluation of genetic diversity for this species and other related Pangasius species.     

Characterization of an aminotransferase from Acanthamoeba polyphaga Mimivirus

Acanthamoeba polyphaga Mimivirus, a complex virus that infects amoeba, was first reported in 2003. It is now known that its DNA genome encodes for nearly 1,000 proteins including enzymes that are required for the biosynthesis of the unusual sugar 4‐amino‐4,6‐dideoxy‐d‐glucose, also known as d‐viosamine. As observed in some bacteria, the pathway for the production of this sugar initiates with a nucleotide‐linked sugar, which in the Mimivirus is thought to be UDP‐d‐glucose. The enzyme required for the installment of the amino group at the C‐4′ position of the pyranosyl moiety is encoded in the Mimivirus by the L136 gene. Here, we describe a structural and functional analysis of this pyridoxal 5′‐phosphate‐dependent enzyme, referred to as L136. For this analysis, three high‐resolution X‐ray structures were determined: the wildtype enzyme/pyridoxamine 5′‐phosphate/dTDP complex and the site‐directed mutant variant K185A in the presence of either UDP‐4‐amino‐4,6‐dideoxy‐d‐glucose or dTDP‐4‐amino‐4,6‐dideoxy‐d‐glucose. Additionally, the kinetic parameters of the enzyme utilizing either UDP‐d‐glucose or dTDP‐d‐glucose were measured and demonstrated that L136 is efficient with both substrates. This is in sharp contrast to the structurally related DesI from Streptomyces venezuelae, whose three‐dimensional architecture was previously reported by this laboratory. As determined in this investigation,DesI shows a profound preference in its catalytic efficiency for the dTDP‐linked sugar substrate. This difference can be explained in part by a hydrophobic patch in DesI that is missing in L136. Notably, the structure of L136 reported here represents the first three‐dimensional model for a virally encoded PLP‐dependent enzyme and thus provides new information on sugar aminotransferases in general.     

大鲵细菌性败血症病原分离及生物学特性研究

利用湖南润孚生物工程公司大鲵人工养殖场10尾具有典型症状的患病大鲵,从体表病灶和体内器官肠、胃、肝、脾、肾等共分离得到9株细菌。通过人工感染试验、细菌形态观察和生理生化实验对其进行鉴定,结果显示引起该养殖场大鲵发病的病原为嗜水气单胞菌。通过回归感染试验发现,其中一菌株对大鲵的致病力很强,死亡率达到100%。药物敏感性试验结果显示,菌株对环丙沙星、头孢曲松、头孢他啶、头孢孟多、头孢哌酮、庆大霉素、头孢西丁药物相对比较敏感,而对克林霉素、头孢唑林、甲硝唑和复方新诺明具有耐药性。     

The Interaction of Equine Lysozyme:Oleic Acid Complexes with Lipid Membranes Suggests a Cargo Off-Loading Mechanism

The normal function of equine lysozyme (EL) is the hydrolysis of peptidoglycan residues of bacterial cell walls. EL is closely related to α-lactalbumins with respect to sequence and structure and further possesses the calcium binding site of α-lactalbumins. Recently, EL multimeric complexes with oleic acids (ELOAs) were shown to possess tinctorial and morphological properties, similar to amyloidal aggregates, and to be cytotoxic. ELOA's interactions with phospholipid membranes appear to be central to its biological action, similar to human α-lactalbumin made lethal to tumor cells. Here, we describe the interaction of ELOA with phospholipid membranes. Confocal scanning laser microscopy shows that ELOA, but not native EL, accumulates on the surface of giant unilamellar vesicles, without inducing significant membrane permeability. Quartz crystal microbalance with dissipation data indicated an essentially non-disruptive binding of ELOA to supported lipid bilayers, leading to formation of highly dissipative and “soft” lipid membrane; at higher concentrations of ELOA, the lipid membrane desorbs from the surface probably as bilayer sheets of vesicles. This membrane rearrangement occurred to a similar extent when free oleic acid (OA) was added, but not when free OA was removed from ELOA by prior incubation with bovine serum albumin, emphasizing the role of OA in this process. NMR data indicated an equilibrium between free and bound OA, which shifts towards free OA as ELOA is progressively diluted, indicating that OA is relatively loosely bound. Activity measurements together with fluorescence spectroscopy and circular dichroism suggested a conversion of ELOA towards a more native-like state on interaction with lipid membranes, although complete refolding was not observed. Altogether, these results suggest that ELOA may act as an OA carrier and facilitate OA transfer to the membrane. ELOA's properties illustrate that protein folding variants may possess specific functional properties distinct from the native protein.     

Male Body Size and Mating Success and Their Relation to Larval Host Plant History in the Moth Rothschildia lebeau in Costa Rican Dry Forest

The moth Rothschildia lebeau uses three tree species as its primary larval hosts in the tropical dry forest of northwestern Costa Rica. These hosts were shown previously to have different relative effects on caterpillar performance, resulting in an apparent host-related life history trade-off between large adult body size on the one hand but low offspring survival on the other. To further assess the potential ecological and evolutionary importance of this trade-off, an observational field study of the relationship between male body size and mating success was conducted. Across mating trials, larger males had a higher probability of being observed mating. Independent of the effect of size, the amount of wing damage an individual had sustained (a measure of relative age) was negatively correlated with the probability a male was observed mating. Within mating trials, the mated male tended to be larger than the average unmated male, but there was no difference in wing damage. Overall, results of this study were consistent with a positive effect of male body size on mating success, consistent with the idea that larval host plant history and its effects on adult body size matters in terms of adult male fitness. However, all sized males were observed mating over the course of the study, and the size advantage did not appear to be particularly strong.     

Brain gangliosides in axon-myelin stability and axon regeneration

Gangliosides, sialic acid-bearing glycosphingolipids, are expressed at high abundance and complexity in the brain. Altered ganglioside expression results in neural disorders, including seizures and axon degeneration. Brain gangliosides function, in part, by interacting with a ganglioside-binding lectin, myelin-associated glycoprotein (MAG). MAG, on the innermost wrap of the myelin sheath, binds to gangliosides GD1a and GT1b on axons. MAG-ganglioside binding ensures optimal axon-myelin cell-cell interactions, enhances long-term axon-myelin stability and inhibits axon outgrowth after injury. Knowledge of the molecular interactions of brain gangliosides may improve understanding of axon-myelin stability and provide opportunities to enhance recovery after nerve injury.     

Patch-clamp Capacitance Measurements and Ca2+ Imaging at Single Nerve Terminals in Retinal Slices

Visual stimuli are detected and conveyed over a wide dynamic range of light intensities and frequency changes by specialized neurons in the vertebrate retina. Two classes of retinal neurons, photoreceptors and bipolar cells, accomplish this by using ribbon-type active zones, which enable sustained and high-throughput neurotransmitter release over long time periods. ON-type mixed bipolar cell (Mb) terminals in the goldfish retina, which depolarize to light stimuli and receive mixed rod and cone photoreceptor input, are suitable for the study of ribbon-type synapses both due to their large size (~10-12 μm diameter) and to their numerous lateral and reciprocal synaptic connections with amacrine cell dendrites. Direct access to Mb bipolar cell terminals in goldfish retinal slices with the patch-clamp technique allows the measurement of presynaptic Ca²⁺ currents, membrane capacitance changes, and reciprocal synaptic feedback inhibition mediated by GABA_A and GABA_C receptors expressed on the terminals. Presynaptic membrane capacitance measurements of exocytosis allow one to study the short-term plasticity of excitatory neurotransmitter release ^14,15. In addition, short-term and long-term plasticity of inhibitory neurotransmitter release from amacrine cells can also be investigated by recordings of reciprocal feedback inhibition arriving at the Mb terminal ²¹. Over short periods of time (e.g. ~10 s), GABAergic reciprocal feedback inhibition from amacrine cells undergoes paired-pulse depression via GABA vesicle pool depletion ¹¹. The synaptic dynamics of retinal microcircuits in the inner plexiform layer of the retina can thus be directly studied.The brain-slice technique was introduced more than 40 years ago but is still very useful for the investigation of the electrical properties of neurons, both at the single cell soma, single dendrite or axon, and microcircuit synaptic level ¹⁹. Tissues that are too small to be glued directly onto the slicing chamber are often first embedded in agar (or placed onto a filter paper) and then sliced ^{20, 23, 18, 9}. In this video, we employ the pre-embedding agar technique using goldfish retina. Some of the giant bipolar cell terminals in our slices of goldfish retina are axotomized (axon-cut) during the slicing procedure. This allows us to isolate single presynaptic nerve terminal inputs, because recording from axotomized terminals excludes the signals from the soma-dendritic compartment. Alternatively, one can also record from intact Mb bipolar cells, by recording from terminals attached to axons that have not been cut during the slicing procedure. Overall, use of this experimental protocol will aid in studies of retinal synaptic physiology, microcircuit functional analysis, and synaptic transmission at ribbon synapses.     

Intercellular communication via the endo-lysosomal system: Translocation of granzymes through membrane barriers

Cytotoxic lymphocytes (CLs) are responsible for the clearance of virally infected or neoplastic cells. CLs possess specialised lysosome-related organelles called granules which contain the granzyme family of serine proteases and perforin. Granzymes may induce apoptosis in the target cell when delivered by the pore forming protein, perforin. Here we follow the perforin-granzyme pathway from synthesis and storage in the granule, to exocytosis and finally delivery into the target cell. This review focuses on the controversial subject of perforin-mediated translocation of granzymes into the target cell cytoplasm. It remains unclear whether this occurs at the cell surface with granzymes moving through a perforin pore in the plasma membrane, or if it involves internalisation of perforin and granzymes and subsequent release from an endocytic compartment. The latter mechanism would represent an example of cross talk between the endo-lysosomal pathways of individual cells. This article is part of a Special Issue entitled: Proteolysis 50 years after the discovery of lysosome.