IDENTIFICATION OF LECTINS IN THE KINETIDS OF TETRAHYMENA PYRIFORMIS

Previously we described lectin-like molecules in the ciliate Tetrahymena pyriformis; by application of synthetic neoglycoconjugates it is now shown that T. pyriformis contains considerable amounts of both a β-d-glucose- and a lactose-specific lectin. No evidence for the presence of α-d-mannose-, α-d-galactose- or of α-l-fucose-specific lectins could be obtained. The two lectins, identified in T. pyriformis, are associated with the kinetids. During cell division the lectins disappear or become masked in the fission furrow. Therefore, we assume that these lectins are involved in the organization of the distribution pattern of the kinetids during cell division perhaps due to lectin—glycoprotein interactions.     

Tube-Like Structures with Co-Expression of D2-40 and CD34: Newly Formed Vasculatures?

Background: A great number of in vitro and in vivo studies have suggested that many pathways or factors can stimulate angiogenesis and lymphangiogenesis, which facilitate tumor progression and metastasis. However, the morphological and immunohistochemical profile of newly formed vasculatures has not been elucidated, making it difficult to differentiate them from the pre-existing ones, and to identify their unique molecular profiles for diagnosis and therapeutic interventions.Experimental findings: As cytokeratin (CK)-19 is a well-recognized stem cell marker and CK-19-positive cells are frequently detected in the peripheral blood of patients with metastatic cancer, our recent studies have assessed the involvement of CK-19 in the formation of new vasculatures in primary colorectal cancer (CRC) tissues. Our studies showed that a subset of lymph node-positive cases harbored some isolated normal epithelial structures with distinct CK-19 immunostaining within an otherwise CK-19-negative background. These structures are exclusively located within or adjacent to lymphoid follicles and are often surrounded by tube-like structures expressing lymphatic endothelial marker D2-40. Similar structures are more frequently seen at the junctions between pre-invasive and invasive CRC with the following features: (1). they consist of a single layer of endothelial cells that express both D2-40 and CD34, (2). their endothelial walls are often incomplete with disseminated cells protruding into the adjacent stroma, and (3). they are exclusively associated with disseminated CK-19-positive cellsHypothesis: Based on these findings, we propose that these tube-like structures represent newly formed vasculatures, which are derived by the convergence of aberrant lymphocyte infiltration and tumor stem cells. Because of their close physical proximity, tumor stem cells within the epithelial and stromal components contribute equally and coordinately to the morphogenesis of new vasculatures, which constitutes the basis for the unique morphologic and immunohistochemical features of newly formed vasculatures. Our hypothesis appears to be applicable to all epithelium-derived cancers.     

Temporal variability in the spatial and environmental determinants of functional metacommunity organization – stream fish in a human‐modified landscape

1. Quantifying the relative importance of environmental filtering versus regional spatial structuring has become an intensively studied area in the context of metacommunity ecology. However, most studies have evaluated the role of environmental and spatial processes using taxonomic data sets of single snapshot surveys. 2. Here, we examined temporal changes in patterns and possible processes behind the functional metacommunity organization of stream fishes in a human‐modified landscape. Specifically, we (i) studied general changes in the functional composition of fish assemblages among 40 wadeable stream sites during a 3‐year study period in the catchment area of Lake Balaton, Hungary, (ii) quantified the relative importance of spatial and environmental factors as determinants of metacommunity structure and (iii) examined temporal variability in the relative role of spatial and environmental processes for this metacommunity. 3. Partial triadic analysis showed that assemblages could be effectively ordered along a functional gradient from invertebrate consuming species dominated by the opportunistic life‐history strategy, to assemblages with a diverse array of functional attributes. The analysis also revealed that functional fish assemblage structure was moderately stable among the sites between the sampling periods. 4. Despite moderate stability, variance partitioning using redundancy analyses (RDA) showed considerable temporal variability in the contribution of environmental and spatial factors to this pattern. The analyses also showed that environmental variables were, in general, more important than spatial ones in determining metacommunity structure. Of these, natural environmental variables (e.g. altitude, velocity) proved to be more influential than human‐related effects (e.g. pond area, % inhabited area above the site, nutrient enrichment), even in this landscape with relatively low variation in altitude and stream size. 5. Pond area was, however, the most important human stressor variable that was positively associated with the abundance of non‐native species with diverse functional attributes. The temporal variability in the relative importance of environmental and spatial factors was probably shaped by the release of non‐native fish from fish ponds to the stream system during flood events. 6. To conclude, both spatial processes and environmental control shape the functional metacommunity organization of stream fish assemblages in human‐modified landscapes, but their importance can vary in time. We argue, therefore, that metacommunity studies should better consider temporal variability in the ecological mechanisms (e.g. dispersal limitation, species sorting) that determine the dynamics of landscape‐level community organization.     

Low Resolution Solution Structure of HAMLET and the Importance of Its Alpha-Domains in Tumoricidal Activity

HAMLET (Human Alpha-lactalbumin Made LEthal to Tumor cells) is the first member in a new family of protein-lipid complexes with broad tumoricidal activity. Elucidating the molecular structure and the domains crucial for HAMLET formation is fundamental for understanding its tumoricidal function. Here we present the low-resolution solution structure of the complex of oleic acid bound HAMLET, derived from small angle X-ray scattering data. HAMLET shows a two-domain conformation with a large globular domain and an extended part of about 2.22 nm in length and 1.29 nm width. The structure has been superimposed into the related crystallographic structure of human α-lactalbumin, revealing that the major part of α-lactalbumin accommodates well in the shape of HAMLET. However, the C-terminal residues from L105 to L123 of the crystal structure of the human α-lactalbumin do not fit well into the HAMLET structure, resulting in an extended conformation in HAMLET, proposed to be required to form the tumoricidal active HAMLET complex with oleic acid. Consistent with this low resolution structure, we identified biologically active peptide epitopes in the globular as well as the extended domains of HAMLET. Peptides covering the alpha1 and alpha2 domains of the protein triggered rapid ion fluxes in the presence of sodium oleate and were internalized by tumor cells, causing rapid and sustained changes in cell morphology. The alpha peptide-oleate bound forms also triggered tumor cell death with comparable efficiency as HAMLET. In addition, shorter peptides corresponding to those domains are biologically active. These findings provide novel insights into the structural prerequisites for the dramatic effects of HAMLET on tumor cells.     

Life history predicts advancement of avian spring migration in response to climate change

An increasing number of studies demonstrate that plant and animal phenologies such as the timing of bird migration have been advancing over the globe, likely as a result of climate change. Even closely related species differ in their phenological responses, and the sources of this variation are poorly established. We used a large, standardized dataset of first arrival dates (FAD) of migratory birds to test the effects of phylogenetic relationships and various life-history and ecological traits on the degree to which different species adapt to climate change by earlier migration in spring. Using the phylogenetic comparative method, we found that the advancement of FAD was greater in species with more generalized diet, shorter migration distance, more broods per year, and less extensive prebreeding molt. In turn, we found little evidence that FAD trends were influenced by competition for mating (polygamy or extra-pair paternity) and breeding opportunities (cavity nests). Our findings were robust to several potentially confounding effects. These evolutionary correlations, coupled with the low levels of phylogenetic dependence we found, indicate that avian migration phenology adapts to climate change as a species-specific response. Our results suggest that the degree of this response is fundamentally shaped by constraints and selection pressures of the species' life history, and less so by the intensity of sexual selection.     

Phytochelatin biosynthesis and function in heavy-metal detoxification

Plants respond to heavy-metal toxicity via a number of mechanisms. One such mechanism involves the chelation of heavy metals by a family of peptide ligands, the phytochelatins. Molecular genetic approaches have resulted in important advances in our understanding of phytochelatin biosynthesis. In particular, genes encoding the enzyme phytochelatin synthase have been isolated from plant and yeast species. Unexpectedly, genes with similar sequences to those encoding phytochelatin synthase have been identified in some animal species.     

Isolation and analysis of aroFo mutants by using an aroF-lac operon fusion

The lac structural genes were fused to the regulatory region of the aroF-tyrA operon so that the expression of beta-galactosidase was regulated by the tyrR+ gene product. Transducing phage carrying the aroF-lac fusion were isolated, and a lambda aroF-lac lysogen was used to select for aroFo mutants. A plasmid vector was constructed onto which the aroFo mutations were transferred by recombination in vivo.