A holistic approach to marine eco-systems biology

The structure, robustness, and dynamics of ocean plankton ecosystems remain poorly understood due to sampling, analysis, and computational limitations. The Tara Oceans consortium organizes expeditions to help fill this gap at the global level.     

Mixed effects of landscape complexity and farming practice on weed seed removal

Agricultural intensification negatively affects farmland biodiversity, and thereby, ecosystem services such as predation of weed seeds. Landscape complexity (large and diverse areas of semi-natural habitats) and organic farming (without pesticides and mineral fertilizers) can counteract this negative trend, but little is known about their relative importance. We experimentally studied seed removal of four economically relevant weed species by excluding (i) vertebrates, (ii) vertebrates plus large invertebrates and (iii) neither vertebrates nor invertebrates (control) at the field edge and in the interior of 22 organically or conventionally managed winter wheat fields, located across a gradient of landscape complexity (41–94% arable land). Arable land (%) was used as a simple predictor of landscape complexity, as it is closely related to landscape parameters such as habitat type diversity. Seed predation and removal were mainly influenced by large invertebrates, seed species identity, with Cirsium arvense being more affected than Poa trivialis, Apera spica-venti and Galium aparine and landscape complexity in interaction with farming practice, as it increased in conventional fields, but decreased in organic fields as landscape complexity decreased. Seed predation and removal did not consistently correspond to seed predator densities, as small mammal abundances decreased in conventional fields, but increased in organic fields as landscape complexity decreased and carabid activity densities were higher in organic compared to conventional fields. Slug activity density showed same response to landscape complexity and farming practice like seed removal and appeared to additionally influence the movement of seeds. In conclusion, our assessment of interacting local and landscape effect adds to the current knowledge of seed predation and removal. Farming practice and landscape complexity affect seed predator species differentially, thereby resulting in complex pattern of seed predation and removal. The service of weed seed predation is provided by small mammals and invertebrates and the disservice of seed dispersal and movement is provided by slugs.     

State-of-the-art technologies, current opinions and developments, and novel findings: news from the field of histochemistry and cell biology

Investigations of cell and tissue structure and function using innovative methods and approaches have again yielded numerous exciting findings in recent months and have added important data to current knowledge, inspiring new ideas and hypotheses in various fields of modern life sciences. Topics and contents of comprehensive expert reviews covering different aspects in methodological advances, cell biology, tissue function and morphology, and novel findings reported in original papers are summarized in the present review.     

The expression of a hunchback ortholog in the polychaete annelid Platynereis dumerilii suggests an ancestral role in mesoderm development and neurogenesis

Orthologs of the Drosophila gap gene hunchback have been isolated so far only in protostomes. Phylogenetic analysis of recently available genomic data allowed us to confirm that hunchback genes are widely found in protostomes (both lophotrochozoans and ecdysozoans). In contrast, no unequivocal hunchback gene can be found in the genomes of deuterostomes and non-bilaterians. We cloned hunchback in the marine polychaete annelid Platynereis dumerilii and analysed its expression during development. In this species, hunchback displays an expression pattern indicative of a role in mesoderm formation and neurogenesis, and similar to the expression found for hunchback genes in arthropods. These data suggest altogether that these functions are ancestral to protostomes.Pierre Kerner and Fabiola Zelada González contributed equally to this work.     

The landscape context of cereal aphid-parasitoid interactions

Analyses at multiple spatial scales may show how important ecosystem services such as biological control are determined by processes acting on the landscape scale. We examined cereal aphid-parasitoid interactions in wheat fields in agricultural landscapes differing in structural complexity (32-100% arable land). Complex landscapes were associated with increased aphid mortality resulting from parasitism, but also with higher aphid colonization, thereby counterbalancing possible biological control by parasitoids and lastly resulting in similar aphid densities across landscapes. Thus, undisturbed perennial habitats appeared to enhance both pests and natural enemies. Analyses at multiple spatial scales (landscape sectors of 0.5-6 km diameter) showed that correlations between parasitism and percentage of arable land were significant at scales of 0.5-2 km, whereas aphid densities responded to percentage of arable land at scales of 1-6 km diameter. Hence, the higher trophic level populations appeared to be determined by smaller landscape sectors owing to dispersal limitation, showing the 'functional spatial scale' for species-specific landscape management.     

Assembly of natural and recombinant prion protein into fibrils

The conversion of the alpha-helical, cellular isoform of the prion protein (PrP C ) to the insoluble, beta-sheet-rich, infectious, disease-causing isoform (PrP Sc ) is the fundamental event in the prion diseases. The C-terminal fragment of PrP Sc (PrP 27-30) is formed by limited proteolysis and retains infectivity. Unlike full-length PrP Sc , PrP 27-30 polymerizes into rod-shaped structures with the ultra-structural and tinctorial properties of amyloid. To study the folding of PrP, both with respect to the formation of PrP Sc from PrP C and the assembly of rods from PrP 27-30, we solubilized Syrian hamster (sol SHa) PrP 27-30 in low concentrations (0.2%) of sodium dodecyl sulfate (SDS) under conditions previously used to study the structural transitions of this protein. Sol SHaPrP 27-30 adopted a beta-sheet-rich structure at SDS concentrations between 0.02% and 0.04% and remained soluble. Here we report that NaCl stabilizes SHaPrP 27-30 in a soluble, beta-sheet-rich state that allows fibril assembly to proceed over several weeks. Under these conditions, fibril formation occurred not only with sol PrP 27-30, but also with native SHaPrP C . Addition of sphingolipids seems to increase fibril growth. When recombinant (rec) SHaPrP(90-231) was exposed to low concentrations of SDS, similar to those used to polymerize sol SHaPrP 27-30 in the presence of 250 mM NaCl, fibril formation occurred regularly. When fibrils formed from PrP 27-30 or PrP C were bioassayed in transgenic mice overexpressing full-length SHaPrP, no infectivity was obtained, whereas amyloid fibrils formed of rec mouse PrP(89-230) were infectious. At present, it cannot be determined whether the lack of infectivity is caused by a difference in the structure of the fibrils or in the bioassay conditions.     

Protein kinase C-mediated endothelial barrier regulation is caveolin-1-dependent

Protein kinase C (PKC) is activated in response to various inflammatory mediators and contributes significantly to the endothelial barrier breakdown. However, the mechanisms underlying PKC-mediated permeability regulation are not well understood. We prepared microvascular myocardial endothelial cells from both wild-type (WT) and caveolin-1-deficient mice. Activation of PKC by phorbol myristate acetate (PMA) (100 nM) for 30 min induced intercellular gap formation and fragmentation of VE-cadherin immunoreactivity in WT but not in caveolin-1-deficient monolayers. To test the effect of PKC activation on VE-cadherin-mediated adhesion, we allowed VE-cadherin-coated microbeads to bind to the endothelial cell surface and probed their adhesion by laser tweezers. PMA significantly reduced bead binding to 78±6% of controls in WT endothelial cells without any effect in caveolin-1-deficient cells. In WT cells, PMA caused an 86±18% increase in FITC-dextran permeability whereas no increase in permeability was observed in caveolin-1-deficient monolayers. Inhibition of PKC by staurosporine (50 nM, 30 min) did not affect barrier functions in both WT and caveolin-1-deficient MyEnd cells. Theses data indicate that PKC activation reduces endothelial barrier functions at least in part by the reduction of VE-cadherin-mediated adhesion and demonstrate that PKC-mediated permeability regulation depends on caveolin-1.     

Blown fuse regulates stretching and outgrowth but not myoblast fusion of the circular visceral muscles in Drosophila

Circular visceral muscles of Drosophila are binuclear syncytia arising from fusion of two different kinds of myoblasts: a circular visceral founder cell and one visceral fusion-competent myoblast. In contrast to fusion leading to the somatic body-wall musculature, myoblast fusion for the circular visceral muscles does not result in massive syncytia but instead in syncytia interconnected with multiple cytoplasmic bridges, which differentiate into large web-shaped muscles. Here, we show that these syncytial circular visceral muscles build a gut-enclosing network with the interwoven longitudinal visceral muscles. At the ultrastructural level, during circular visceral myoblast fusion and the first step of somatic myoblast fusion prefusion complexes and electron-dense plaques were not detectable which was surprising as these structures are characteristic for the second step of somatic myoblast fusion. Moreover, we demonstrate that Blown fuse (Blow), a cytoplasmic protein essential for the second step of somatic myoblast fusion, plays a different role in circular visceral myogenesis. Blow is known to be essential for progression beyond the prefusion complex in the somatic mesoderm; however, analysis of blow mutants established that it has a restricted role in stretching and outgrowth of the syncytia in the circular visceral muscles. Furthermore, we also found that in the visceral mesoderm, Blow is expressed in both the fusion-competent myoblasts and circular visceral founders, while expression in the somatic mesoderm is initially restricted to fusion-competent myoblasts. We also demonstrate that different enhancer elements in the first intron of blow are responsible for this distinct expression pattern. Thus, we propose a model for Blow in which this protein is involved in at least two clearly differing processes during Drosophila muscle formation, namely somatic myoblast fusion on the one hand and stretching and outgrowth of circular visceral muscles on the other.     

Extensive chordate and annelid macrosynteny reveals ancestral homeobox gene organization

Genes with the homeobox motif are crucial in developmental biology and widely implicated in the evolution of development. The Antennapedia (ANTP)-class is one of the two major classes of animal homeobox genes, and includes the Hox genes, renowned for their role in patterning the anterior-posterior axis of animals. The origin and evolution of the ANTP-class genes are a matter of some debate. A principal guiding hypothesis has been the existence of an ancient gene Mega-cluster deep in animal ancestry. This hypothesis was largely established from linkage data from chordates, and the Mega-cluster hypothesis remains to be seriously tested in protostomes. We have thus mapped ANTP-class homeobox genes to the chromosome level in a lophotrochozoan protostome. Our comparison of gene organization in Platynereis dumerilii and chordates indicates that the Mega-cluster, if it did exist, had already been broken up onto four chromosomes by the time of the protostome-deuterostome ancestor (PDA). These results not only elucidate an aspect of the genome organization of the PDA but also reveal high levels of macrosynteny between P. dumerilii and chordates. This implies a very low rate of interchromosomal genome rearrangement in the lineages leading to P. dumerilii and the chordate ancestor since the time of the PDA.