Growth factor-induced MAPK network topology shapes Erk response determining PC-12 cell fate

The mitogen-activated protein kinase (MAPK) network is a conserved signalling module that regulates cell fate by transducing a myriad of growth-factor signals. The ability of this network to coordinate and process a variety of inputs from different growth-factor receptors into specific biological responses is, however, still not understood. We investigated how the MAPK network brings about signal specificity in PC-12 cells, a model for neuronal differentiation. Reverse engineering by modular-response analysis uncovered topological differences in the MAPK core network dependent on whether cells were activated with epidermal or neuronal growth factor (EGF or NGF). On EGF stimulation, the network exhibited negative feedback only, whereas a positive feedback was apparent on NGF stimulation. The latter allows for bi-stable Erk activation dynamics, which were indeed observed. By rewiring these regulatory feedbacks, we were able to reverse the specific cell responses to EGF and NGF. These results show that growth factor context determines the topology of the MAPK signalling network and that the resulting dynamics govern cell fate.     

Molecular determinants of caste differentiation in the highly eusocial honeybee <Emphasis Type="Italic">Apis mellifera</Emphasis>

Background  

In honeybees, differential feeding of female larvae promotes the occurrence of two different phenotypes, a queen and a worker, from identical genotypes, through incremental alterations, which affect general growth, and character state alterations that result in the presence or absence of specific structures. Although previous studies revealed a link between incremental alterations and differential expression of physiometabolic genes, the molecular changes accompanying character state alterations remain unknown.     

The use of ASB-14 in combination with CHAPS is the best for solubilization of human brain proteins for two-dimensional gel electrophoresis.

Protein extraction is the most important step to reveal a proteome by Two-Dimensional Gel Electrophoresis. Usually, the urea/thiourea based standard protein extraction buffer (SB) is combined with detergents with the aim of achieving better resolution and solubilization of different classes of proteins. In order to produce better gels and achieve the greatest spot resolution of Human Brain Proteins, comparisons using 2-DE of extracted proteins from Human Brain Frontal Cortex with SB constituents (7M Urea, 2M Thiourea and 100mM DTT) were made, using different detergent compositions in the buffer. SB preparations in combination with CHAPS and ASB-14 as well as with ASB-16 (reported for the first time in 2-DE experiments) have been tested. Our results confirm that the most efficient solubilizing solution for 2-DE analysis of cytosolic and membrane Human Brain Proteins is SB combined with 4% CHAPS and 2% ASB-14.     

Dynamic interaction of HIV-1 Nef with the clathrin-mediated endocytic pathway at the plasma membrane

The HIV-1 Nef protein perturbs the trafficking of membrane proteins such as CD4 by interacting with clathrin-adaptor complexes. We previously reported that Nef alters early/recycling endosomes, but its role at the plasma membrane is poorly documented. Here, we used total internal reflection fluorescence microscopy, which restricts the analysis to a approximately 100 nm region of the adherent surface of the cells, to focus on the dynamic of Nef at the plasma membrane relative to that of clathrin. Nef colocalized both with clathrin spots (CS) that remained static at the cell surface, corresponding to clathrin-coated pits (CCPs), and with approximately 50% of CS that disappeared from the cell surface, corresponding to forming clathrin-coated vesicles (CCVs). The colocalization of Nef with clathrin required the di-leucine motif essential for Nef binding to AP complexes and was independent of CD4 expression. Furthermore, analysis of Nef mutants showed that the capacity of Nef to induce internalization and downregulation of CD4 in T lymphocytes correlated with its localization into CCPs. In conclusion, this analysis shows that Nef is recruited into CCPs and into forming CCVs at the plasma membrane, in agreement with a model in which Nef uses the clathrin-mediated endocytic pathway to induce internalization of some membrane proteins from the surface of HIV-1-infected T cells.     

Analysis and interpretation of dynamic FDG PET oncological studies using data reduction techniques

Background  

Dynamic positron emission tomography studies produce a large amount of image data, from which clinically useful parametric information can be extracted using tracer kinetic methods. Data reduction methods can facilitate the initial interpretation and visual analysis of these large image sequences and at the same time can preserve important information and allow for basic feature characterization.     

Floral resource partitioning by social wasps (Hymenoptera: Vespidae) and bees (Hymenoptera: Apoidea) in an area of caatinga in Brazil

Wasps and bees are important components of flower visitor guilds in the Neotropical region. The abundance of social wasps and bees, collected during flower visits, was used to calculate niche breadth and niche overlap indices, in order to characterize the utilization of the floral resources by those insects. Samples were taken monthly, for 13 months (156h), by two collectors which captured the specimens on flowers using entomological nets, while walking along a way in an area of caatinga at Itatim, State of Bahia, Brazil. Wasps and bees heavily visited a few sources of floral resources, but the most visited plants by each group were different, and few plant species were important for both groups, resulting in low niche overlap between bees and wasps. The niche overlap among wasp species was generally higher than among bee species. The general overlap, which takes into consideration all species together was low (< 30%).     

Biomass and population structure of Constrictotermes cyphergaster (Silvestri) (Isoptera: termitidae) in the dry forest of caatinga, northeastern Brazil

Biomass and population structure of Constrictotermes cyphergaster (Silvestri) were studied in an area of dry forest of caatinga in the State of Paraiba, northeastern Brazil. Twelve nests of different sizes were randomly collected, being six during the dry season (November 2004 and 2005) and six during the wet season (March 2004). Soldier and worker populations varied between 4880 and 118800 individuals per nest. The ratio between soldiers and workers did not significantly vary between seasons. Biomass (measured as fresh weight) of individuals varied between 13.9 and 408.8 g per nest, and soldiers and workers had significantly greater biomass during the wet season. The estimated density of nests of C. cyphergaster was 59.0 +/- 22.53 active nests/ha. Quantitative data of the study colonies and data on the nest abundance showed that C. cyphergaster encompassed some 278.2 individuals/m(2), with approximately 0.9 g (fresh weight)/m(2). These data suggest that C. cyphergaster is an important consumer of vegetal matter and, therefore, an important species affecting the nutrient cycling and energy flow in the caatinga vegetation.     

Protein oxidation, repair mechanisms and proteolysis in Saccharomyces cerevisiae

Reactive oxygen species, generated as normal by-products of aerobic metabolism or due to cellular stress, oxidize molecules and cause cell death by apoptosis. The accumulation of oxidized proteins is a hallmark of aging and a number of aging diseases. Oxidation can impair protein function as the proteins are unfolded leading to an increase of protein hydrophobicity and often resulting in the formation of toxic aggregates. The yeast Saccharomyces cerevisiae has been used as a eukaryotic model system to analyze the molecular mechanisms of oxidative stress protection. This paper reviews how the identification in yeast of specific damaged proteins has provided new insights into mechanisms of cytotoxicity and highlights the role of repair and degradative processes, including vacuolar/lysosomal and proteasomal proteolysis, in housekeeping after protein oxidative damage.