Niche partitioning due to adaptive foraging reverses effects of nestedness and connectance on pollination network stability

Much research debates whether properties of ecological networks such as nestedness and connectance stabilise biological communities while ignoring key behavioural aspects of organisms within these networks. Here, we computationally assess how adaptive foraging (AF) behaviour interacts with network architecture to determine the stability of plant–pollinator networks. We find that AF reverses negative effects of nestedness and positive effects of connectance on the stability of the networks by partitioning the niches among species within guilds. This behaviour enables generalist pollinators to preferentially forage on the most specialised of their plant partners which increases the pollination services to specialist plants and cedes the resources of generalist plants to specialist pollinators. We corroborate these behavioural preferences with intensive field observations of bee foraging. Our results show that incorporating key organismal behaviours with well‐known biological mechanisms such as consumer‐resource interactions into the analysis of ecological networks may greatly improve our understanding of complex ecosystems.     

The levels of both lipid rafts and raft-located acetylcholinesterase dimers increase in muscle of mice with muscular dystrophy by merosin deficiency

Wild type and dystrophic (merosin-deficient) Lama2dy mice muscles were compared for their density of lipid rafts. The 5-fold higher level of caveolin-3 and the 2-3 times higher level of ecto-5’-nucleotidase activity in raft preparations (Triton X-100-resistant membranes) of dystrophic muscle supported expansion of caveolar and non-caveolar lipid rafts. The presence in rafts of glycosylphosphatidylinositol (GPI)-linked acetylcholinesterase (AChE) dimers, which did not arise from erythrocyte or nerve, not only revealed for the first time the capacity of the myofibre for translating the AChE-H mRNA but also an unrecognized pathway for targeting AChE-H to specialized membrane domains of the sarcolemma. Rafts of dystrophic muscle contained a 5-fold higher AChE activity/mg protein. RT-PCR for 3’-alternative mRNAs of AChE revealed AChE-T mRNA prevailing over AChE-R and AChE-H mRNAs in wild type mouse muscle. It also displayed principal 5’-alternative AChE mRNAs with exons E1c and E1e (the latter coding for N-terminally extended subunits) and fewer with E1d, E1a and E1b. The levels of AChE and butyrylcholinesterase mRNAs were unaffected by dystrophy. Finally, the decreased level of proline-rich membrane anchor (PRiMA) mRNA in Lama2dy muscle provided for a rational explanation to the loss of PRiMA-bearing AChE tetramers in dystrophic muscle.     

Fibronectin promotes differentiation of neural crest progenitors endowed with smooth muscle cell potential

The neural crest (NC) is a model system used to investigate multipotency during vertebrate development. Environmental factors control NC cell fate decisions. Despite the well-known influence of extracellular matrix molecules in NC cell migration, the issue of whether they also influence NC cell differentiation has not been addressed at the single cell level. By analyzing mass and clonal cultures of mouse cephalic and quail trunk NC cells, we show for the first time that fibronectin (FN) promotes differentiation into the smooth muscle cell phenotype without affecting differentiation into glia, neurons, and melanocytes. Time course analysis indicated that the FN-induced effect was not related to massive cell death or proliferation of smooth muscle cells. Finally, by comparing clonal cultures of quail trunk NC cells grown on FN and collagen type IV (CLIV), we found that FN strongly increased both NC cell survival and the proportion of unipotent and oligopotent NC progenitors endowed with smooth muscle potential. In contrast, melanocytic progenitors were prominent in clonogenic NC cells grown on CLIV. Taken together, these results show that FN promotes NC cell differentiation along the smooth muscle lineage, and therefore plays an important role in fate decisions of NC progenitor cells.     

Identifying a Kinase Network Regulating FGF14:Nav1.6 Complex Assembly Using Split-Luciferase Complementation

Kinases play fundamental roles in the brain. Through complex signaling pathways, kinases regulate the strength of protein:protein interactions (PPI) influencing cell cycle, signal transduction, and electrical activity of neurons. Changes induced by kinases on neuronal excitability, synaptic plasticity and brain connectivity are linked to complex brain disorders, but the molecular mechanisms underlying these cellular events remain for the most part elusive. To further our understanding of brain disease, new methods for rapidly surveying kinase pathways in the cellular context are needed. The bioluminescence-based luciferase complementation assay (LCA) is a powerful, versatile toolkit for the exploration of PPI. LCA relies on the complementation of two firefly luciferase protein fragments that are functionally reconstituted into the full luciferase enzyme by two interacting binding partners. Here, we applied LCA in live cells to assay 12 kinase pathways as regulators of the PPI complex formed by the voltage-gated sodium channel, Nav1.6, a transmembrane ion channel that elicits the action potential in neurons and mediates synaptic transmission, and its multivalent accessory protein, the fibroblast growth factor 14 (FGF14). Through extensive dose-dependent validations of structurally-diverse kinase inhibitors and hierarchical clustering, we identified the PI3K/Akt pathway, the cell-cycle regulator Wee1 kinase, and protein kinase C (PKC) as prospective regulatory nodes of neuronal excitability through modulation of the FGF14:Nav1.6 complex. Ingenuity Pathway Analysis shows convergence of these pathways on glycogen synthase kinase 3 (GSK3) and functional assays demonstrate that inhibition of GSK3 impairs excitability of hippocampal neurons. This combined approach provides a versatile toolkit for rapidly surveying PPI signaling, allowing the discovery of new modular pathways centered on GSK3 that might be the basis for functional alterations between the normal and diseased brain.     

Reducing GBA2 Activity Ameliorates Neuropathology in Niemann-Pick Type C Mice

The enzyme glucocerebrosidase (GBA) hydrolyses glucosylceramide (GlcCer) in lysosomes. Markedly reduced GBA activity is associated with severe manifestations of Gaucher disease including neurological involvement. Mutations in the GBA gene have recently also been identified as major genetic risk factor for Parkinsonism. Disturbed metabolism of GlcCer may therefore play a role in neuropathology. Besides lysosomal GBA, cells also contain a non-lysosomal glucosylceramidase (GBA2). Given that the two β-glucosidases share substrates, we speculated that over-activity of GBA2 during severe GBA impairment might influence neuropathology. This hypothesis was studied in Niemann-Pick type C (Npc1 ^-/-) mice showing secondary deficiency in GBA in various tissues. Here we report that GBA2 activity is indeed increased in the brain of Npc1 ^-/- mice. We found that GBA2 is particularly abundant in Purkinje cells (PCs), one of the most affected neuronal populations in NPC disease. Inhibiting GBA2 in Npc1 ^-/- mice with a brain-permeable low nanomolar inhibitor significantly improved motor coordination and extended lifespan in the absence of correction in cholesterol and ganglioside abnormalities. This trend was recapitulated, although not to full extent, by introducing a genetic loss of GBA2 in Npc1 ^-/- mice. Our findings point to GBA2 activity as therapeutic target in NPC.     

Morphological Variation in Wild Marmosets (Callithrix penicillata and C. geoffroyi) and Their Hybrids

Evolutionary theory and observation predict wider phenotypic variation in hybrids than parental species. Emergent phenotypic novelty in hybrids may in turn drive new adaptations or speciation by breaking parental phenotypic constraints. Primate hybridization is often documented through genetic evidence, but knowledge about the primate hybrid phenotype remains limited due to a small number of available studies on hybrid primate morphology. Here, we examine pelage and morphometric variation in two Brazilian marmoset species (Callithrix penicillata and C. geoffroyi) and their hybrids. Hybrids were sampled in an anthropogenic hybrid zone in the municipality of Viçosa, Minas Gerais state, Brazil. We analyzed hybrid facial and body pelage color variation, and compared 13 morphometric measures between hybrids and parental species. Five different hybrid facial morphotypes were observed, varying from intermediate to parental-like. Hybrid facial morphotypes were biased towards C. penicillata, suggesting that the pelage of this species may be dominant to that of C. geoffroyi in this context, and indicating that mate preference, and therefore gene flow/introgression, may be biased towards C. penicillata within the hybrid zone. Hybrid morphometric features were on average intermediate to parental species traits, but transgressive hybrids were also observed, suggesting that morphometric variation for the studied traits is consistent with Rieseberg’s complementary allele model. Finally, we observed a decoupling of facial patterning and size/shape in hybrids, relative to parent phenotypes, suggesting that an important factor driving phenotypic novelty within the Viçosa marmoset hybrid zone might be the loosening of evolutionary constraints on phenotypic trait integration.     

Water relations of cassava cultivated under water-deficit levels

The tolerance of plants to water deficit involves a series of adaptive mechanisms; however, little is known about the physiological characteristics of cassava (Manihot esculenta Crantz), which is one of the most tolerant crops to adverse environmental conditions. The objective of this work was to evaluate the water relations in cassava plants subjected to different levels of water deficit. The treatments were conducted in three evaluation periods (0, 45 and 90 days after water deficit) and at three soil water tensions (? 10, ? 40 and ? 70 kPa), with five replicates. The plants were mainly affected at 45 days after the water deficit, with an increase of 42.9% in total chlorophyll content and 35.3% in carotenoid content in plants under a tension of ? 70 kPa; however, these plants reduced by 30.8% chlorophyll a content at 90 days of the treatments. The water potential, relative water content and electrolyte leakage in the leaf were not altered by the soil water tension. There was an increase of 35.4% in stomatal density independent of soil water status at 90 days and of 16.0% under tensions of ? 40 and ? 70 kPa; however, the effective quantum efficiency of photosystem II and rate of electron transport were reduced. Cassava can maintain a leaf water potential close to ? 0.3 MPa in the predawn and the integrity of the cell membranes in leaves under a soil water tension of up to ? 70 kPa.     

Simvastatin rises reactive oxygen species levels and induces senescence in human melanoma cells by activation of p53/p21 pathway

Recent studies demonstrated that simvastatin has antitumor properties in several types of cancer cells, mainly by inducing apoptosis and inhibiting growth. The arrest of proliferation is a feature of cellular senescence; however, the occurrence of senescence in melanoma cells upon simvastatin treatment has not been investigated until now. Our results demonstrated that exposure of human metastatic melanoma cells (WM9) to simvastatin induces a senescent phenotype, characterized by G1 arrest, positive staining for senescence-associated β-galactosidase assay, and morphological changes. Also, the main pathways leading to cell senescence were examined in simvastatin-treated human melanoma cells, and the expression levels of phospho-p53 and p21 were upregulated by simvastatin, suggesting that cell cycle regulators and DNA damage pathways are involved in the onset of senescence. Since simvastatin can act as a pro-oxidant agent, and oxidative stress may be related to senescence, we measured the intracellular ROS levels in WM9 cells upon simvastatin treatment. Interestingly, we found an increased amount of intracellular ROS in these cells, which was accompanied by elevated expression of catalase and peroxiredoxin-1. Collectively, our results demonstrated that simvastatin can induce senescence in human melanoma cells by activation of p53/p21 pathway, and that oxidative stress may be related to this process.     

Genotoxicity of Nicotiana tabacum leaves on Helix aspersa

Tobacco farmers are routinely exposed to complex mixtures of inorganic and organic chemicals present in tobacco leaves. In this study, we examined the genotoxicity of tobacco leaves in the snail Helix aspersa as a measure of the risk to human health. DNA damage was evaluated using the micronucleus test and the Comet assay and the concentration of cytochrome P450 enzymes was estimated. Two groups of snails were studied: one fed on tobacco leaves and one fed on lettuce (Lactuca sativa L) leaves (control group). All of the snails received leaves (tobacco and lettuce leaves were the only food provided) and water ad libitum. Hemolymph cells were collected after 0, 24, 48 and 72 h. The Comet assay and micronucleus test showed that exposure to tobacco leaves for different periods of time caused significant DNA damage. Inhibition of cytochrome P450 enzymes occurred only in the tobacco group. Chemical analysis indicated the presence of the alkaloid nicotine, coumarins, saponins, flavonoids and various metals. These results show that tobacco leaves are genotoxic in H. aspersa and inhibit cytochrome P450 activity, probably through the action of the complex chemical mixture present in the plant.