Epigenetic Basis of Morphological Variation and Phenotypic Plasticity in Arabidopsis thaliana

Epigenetics is receiving growing attention in the plant science community. Epigenetic modifications are thought to play a particularly important role in fluctuating environments. It is hypothesized that epigenetics contributes to plant phenotypic plasticity because epigenetic modifications, in contrast to DNA sequence variation, are more likely to be reversible. The population of decrease in DNA methylation 1-2 (ddm1-2)-derived epigenetic recombinant inbred lines (epiRILs) in Arabidopsis thaliana is well suited for studying this hypothesis, as DNA methylation differences are maximized and DNA sequence variation is minimized. Here, we report on the extensive heritable epigenetic variation in plant growth and morphology in neutral and saline conditions detected among the epiRILs. Plant performance, in terms of branching and leaf area, was both reduced and enhanced by different quantitative trait loci (QTLs) in the ddm1-2 inherited epigenotypes. The variation in plasticity associated significantly with certain genomic regions in which the ddm1-2 inherited epigenotypes caused an increased sensitivity to environmental changes, probably due to impaired genetic regulation in the epiRILs. Many of the QTLs for morphology and plasticity overlapped, suggesting major pleiotropic effects. These findings indicate that epigenetics contributes substantially to variation in plant growth, morphology, and plasticity, especially under stress conditions.     

Hsf1 Phosphorylation Generates Cell-to-Cell Variation in Hsp90 Levels and Promotes Phenotypic Plasticity

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Overstimulation of Glutamate Signals Leads to Hippocampal Transcriptional Plasticity in Hamsters

It’s known that neurons in mammalian hibernators are more tolerant to hypoxia than those in non-hibernating species and as a consequence animals are capable of awakening from the arousal state without exhibiting cerebral damages. In addition, evidences have suggested that euthermic hamster neurons display protective adaptations against hypoxia, while those of rats are not capable, even though molecular mechanisms involved in similar neuroprotective strategies have not been yet fully studied. In the present work, overstimulation of glutamatergic receptors NMDA recognized as one of the major death-promoting element in hypoxia, accounted for altered network complexity consistent with a moderate reduction of hippocampal neuronal survival (p < 0.05) in hamsters. These alterations appeared to be featured concomitantly with altered glutamatergic signaling as indicated by significant down-regulation (p < 0.01) of NMDAergic (NR2A) and AMPAergic (GluR1, R2) receptor subtypes together with the metabotropic mGluR5 subtype. Diminished mRNA levels were also reported for NMDA receptor binding factors and namely PSD95 plus DREAM, which exert positive and negative regulatory properties, respectively, on receptor trafficking events. Conversely, involvement of glutamatergic signaling systems on neuronal excitotoxicity was strengthened by the co-activation of GABA_AR-mediated effects as indicated by toxic morphological effects being notably reduced along with up-regulated GluR1, GluR2, mGluR5, DREAM, and Homer1c scaffold proteins when muscimol was added. Overall, these results point to a neuroprotective role of the GABAergic system against excitotoxicity episodes via DREAM-dependent inhibition of NMDA receptor and activation of AMPA receptor plus mGluR5, respectively, thus proposing them as novel therapeutic targets against cerebral ischemic damages in humans.     

Phenotypic Variation in Mangrove Cuckoo (Coccyzus minor) across Its Geographic Range

Mangrove Cuckoo (Coccyzus minor) exhibits substantial phenotypic variation across its geographic range, but the significance of this variation for taxonomy remains unresolved. Using measurements of bill size and ventral color recorded from 274 museum specimens, I found that variation in these traits was clinal. No named subspecies was reciprocally diagnosable from all others, and none was distinguishable from the nominate form, such that previously recognized subspecific distinctions are invalid. Greatest differences in phenotype occurred between populations in Florida, the Bahamas, and the Greater Antilles–characteristically small-billed–and those in the Lesser Antilles, which had larger bills. Phenotypically intermediate individuals on the geographically intermediate islands of Barbuda and Antigua linked these two extremes. Individuals intermediate in bill size and color also characterized populations from throughout the remainder of the range in northern South America and Middle America. Mechanisms maintaining the fairly pronounced phenotypic differences between nearby populations of Greater and Lesser Antillean birds are unknown, yet the geographic proximity of these populations suggests that they probably persist despite occasional gene flow, and may be adaptive.     

Histamine Receptor Expression, Hippocampal Plasticity and Ammonia in Histidine Decarboxylase Knockout Mice

Genetic ablation of the histamine producing enzyme histidine decarboxylase (HDC) leads to alteration in exploratory behaviour and hippocampus-dependent learning. We investigated how brain histamine deficiency in HDC knockout mice (HDC KO) affects hippocampal excitability, synaptic plasticity, and the expression of histamine receptors. No significant alterations in: basal synaptic transmission, long-term potentiation (LTP) in the Schaffer collateral synapses, histamine-induced transient changes in the CA1 pyramidal cell excitability, and the expression of H1 and H2 receptor mRNAs were found in hippocampal slices from HDC KO mice. However, when compared to WT mice, HDC KO mice demonstrated: 1. a stronger enhancement of LTP by histamine, 2. a stronger impairment of LTP by ammonia, 3. no long-lasting potentiation of population spikes by histamine, 4. a decreased expression of H3 receptor mRNA, and 5. less potentiation of population spikes by H3 receptor agonism. Parallel measurements in the hypothalamic tuberomamillary nucleus, the origin of neuronal histamine, demonstrated an increased expression of H3 receptors in HDC KO mice without any changes in the spontaneous firing of “histaminergic” neurons without histamine and their responses to the H3 receptor agonist (R)-α-methylhistamine. We conclude that the absence of neuronal histamine results in subtle changes in hippocampal synaptic transmission and plasticity associated with alteration in the expression of H3 receptors.     

Transgenic Expression of the Dicotyledonous Pattern Recognition Receptor EFR in Rice Leads to Ligand-Dependent Activation of Defense Responses

Plant plasma membrane localized pattern recognition receptors (PRRs) detect extracellular pathogen-associated molecules. PRRs such as Arabidopsis EFR and rice XA21 are taxonomically restricted and are absent from most plant genomes. Here we show that rice plants expressing EFR or the chimeric receptor EFR::XA21, containing the EFR ectodomain and the XA21 intracellular domain, sense both Escherichia coli- and Xanthomonas oryzae pv. oryzae (Xoo)-derived elf18 peptides at sub-nanomolar concentrations. Treatment of EFR and EFR::XA21 rice leaf tissue with elf18 leads to MAP kinase activation, reactive oxygen production and defense gene expression. Although expression of EFR does not lead to robust enhanced resistance to fully virulent Xoo isolates, it does lead to quantitatively enhanced resistance to weakly virulent Xoo isolates. EFR interacts with OsSERK2 and the XA21 binding protein 24 (XB24), two key components of the rice XA21-mediated immune response. Rice-EFR plants silenced for OsSERK2, or overexpressing rice XB24 are compromised in elf18-induced reactive oxygen production and defense gene expression indicating that these proteins are also important for EFR-mediated signaling in transgenic rice. Taken together, our results demonstrate the potential feasibility of enhancing disease resistance in rice and possibly other monocotyledonous crop species by expression of dicotyledonous PRRs. Our results also suggest that Arabidopsis EFR utilizes at least a subset of the known endogenous rice XA21 signaling components.     

The Constitutive Activity of Epidermal Growth Factor Receptor vIII Leads to Activation and Differential Trafficking of Wild-type Epidermal Growth Factor Receptor and erbB2

A constitutively active epidermal growth factor receptor (EGFR) mutant, EGFR variant III (EGFRvIII), has been detected at high frequencies in certain human cancers. This study evaluated transactivation and trafficking of erbB family members as a result of constitutive EGFR activity in a cancer cell line. Expression of EGFRvIII modulated erbB family members through different mechanisms; the erbB3 mRNA level was reduced, whereas wild-type EGFR (wtEGFR) and erbB2 protein levels were diminished, with no change in their mRNA levels, and there was no change in the erbB4 expression level. Both EGFR and erbB2 were internalized as a result of EGFRvIII''s activity and redistributed to the cell surface upon addition of AG1478, an inhibitor of wtEGFR/EGFRvIII catalytic activity. Acute activation of EGFRvIII by removing AG1478 from cells increased phosphorylation of both wtEGFR and erbB2 and caused differential trafficking of EGFRvIII''s activation partners; wtEGFR was directed primarily to lysosomal compartments and partially to recycling compartments, whereas erbB2 was directed primarily to recycling compartments and partially to lysosomal compartments. Our data demonstrate that the constitutive activity of EGFRvIII is sufficient to trigger endocytosis and trafficking of wtEGFR and erbB2, which may play a role in activating signaling pathways that are triggered during receptor endocytosis. (J Histochem Cytochem 58:529–541, 2010)     

Phenotypic Plasticity of Invasive Edge Glioma Stem-like Cells in Response to Ionizing Radiation

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Phenotypic Plasticity of Early and Late Successional Forbs in Response to Shifts in Resources

We compared the phenotypic plasticity of two early successional forbs of nutrient-poor mobile dunes (Agriophyllum squarrosum and Corispermum macrocarpum) and two later successional forbs (weeds) of stabilized, higher nutrient dunes and cropland (Chenopodium acuminatum and Salsola collina) to variations in environmental factors. A controlled (including soil nutrients, water, and population density) greenhouse experiment was conducted in Horqin sandy land, China. Late successional species had high plasticity in growth response to nutrients and water or high performance in high soil nutrients and water, reflecting their higher nutrient habitat. In contrast, the early successional species have low plasticity, reflecting their adaptation to resource-poor early successional soil. Late successional species did not always have higher reproductive effort than early successional species. Plants did not have a uniform strategy of increasing reproductive effort with any environmental stressors. Reproductive effort increased with increasing water availability and decreasing nutrient levels, while density had no effect. Patterns of plasticity traits for late successional species exhibited a complex of Master-of-some and Jack-of-all-trades. Late successional species had higher performance or higher plasticity than early successional species.     

Temporal Gene Expression Variation Associated with Eyespot Size Plasticity in Bicyclus anynana

Seasonal polyphenism demonstrates an organism''s ability to respond to predictable environmental variation with alternative phenotypes, each presumably better suited to its respective environment. However, the molecular mechanisms linking environmental variation to alternative phenotypes via shifts in development remain relatively unknown. Here we investigate temporal gene expression variation in the seasonally polyphenic butterfly Bicyclus anynana. This species shows drastic changes in eyespot size depending on the temperature experienced during larval development. The wet season form (larvae reared over 24°C) has large ventral wing eyespots while the dry season form (larvae reared under 19°C) has much smaller eyespots. We compared the expression of three proteins, Notch, Engrailed, and Distal-less, in the future eyespot centers of the two forms to determine if eyespot size variation is associated with heterochronic shifts in the onset of their expression. For two of these proteins, Notch and Engrailed, expression in eyespot centers occurred earlier in dry season than in wet season larvae, while Distal-less showed no temporal difference between the two forms. These results suggest that differences between dry and wet season adult wings could be due to a delay in the onset of expression of these eyespot-associated genes. Early in eyespot development, Notch and Engrailed may be functioning as repressors rather than activators of the eyespot gene network. Alternatively, temporal variation in the onset of early expressed genes between forms may have no functional consequences to eyespot size regulation and may indicate the presence of an ''hourglass'' model of development in butterfly eyespots.     

Phenotypic Plasticity of Grass Root Anatomy in Response to Light Intensity and Nutrient Supply

The phenotypic plasticity of axial root anatomy was investigatedin response to the availability of above- and below-ground resourcesusing eight grass species of the genera Bromus and Poa. In a7-week garden experiment nutrients were varied by a factor offive and light treatments of 100, 30 and 5·5% daylightwere applied. Both nutrients and light influenced root structure.The effect of nutrients was largely explained by plant size,but this was not the case for light. Shading to 30% daylightled to a higher proportion of stele, larger stelar cells andlarger xylem vessels. This can be understood either as an increasedneed for high transport capacity in the shade, where leaf areais larger but root mass lower than in full daylight, or as anincreased resistance against desiccation, which is more of ahazard in open sites. Under 5·5% daylight, tissue massdensity was reduced due to a lower proportion of stele, thoughxylem characteristics were not influenced when a correctionfor the effect of root cross-sectional area was applied. Thisresponse may be interpreted as a mechanism to maintain rootfunction with a lower investment in biomass when growth is limitedby low irradiance. The results show that the response of a plantto resource limitation is not restricted to those organs responsiblefor the acquisition of that resource. Furthermore, the qualitativeresponse to shading depends on the absolute level of irradiance.For this reason, care is needed when comparing the results ofshading experiments conducted under different irradiances. Copyright2001 Annals of Botany Company Bromus, hydraulic conductivity, light, nutrients, phenotypic plasticity, Poa, Poaceae, root anatomy, stele     

Clonal In Vitro Analysis of Neurotrophin Receptor p75-Immunofluorescent Cells Reveals Phenotypic Plasticity of Primary Rat Olfactory Ensheathing Cells

Clonal in vitro analysis represents a powerful tool for studying cellular differentiation. In the present study, microscope-assisted single cell transfer was combined with immunofluorescence to establish clonal cultures of identified primary rat olfactory ensheathing cells (OECs). During development, OECs originate from the neural crest, a transient population of multipotent cells. Since only neural crest cells have been analyzed at clonal density, it remained unclear whether OECs may retain multipotent features. Neurotrophin receptor p75 (p75^NTR)-immunolabelled rat OECs were seeded at clonal density under visual control using a semiautomated cell selection and transfer device (Quixell?) and emerging clones were analyzed with regard to proliferation and antigenic expression. We demonstrate that OECs from neonatal (P1) and 7 day-old (P7) but not from adult rats formed clones in the presence of OEC- and astrocyte-conditioned media (OEC-CM, A-CM). Cloning efficiency but not in vitro growth of OECs was independent of age but increased upon treatment with OEC-CM. Interestingly, about 75 % of P1 compared to 27 % of P7 OEC clones lost p75^NTR expression during 2 weeks in vitro and acquired immunoreactivity for Thy-1. The observation that primary OECs from P1 lost expression of p75^NTR at clonal density and initiated expression of the fibroblast marker Thy-1 may suggest that their developmental potential is greater than previously anticipated. Since microscope-assisted selection of immunofluorescent cells combined with semiautomated transfer guarantees monoclonality in a single step and affords selection of cells according to fluorescent label and/or morphological criteria it may be relevant for a variety of other cell types.     

Eavesdropping on Male Singing Interactions Leads to Differential Allocation in Eggs

Females invest differently in their eggs depending on the quality of their mates. In oscines, female investment is influenced by the quality of male song. In domestic canaries Serinus canaria, as well as in black‐capped chickadees Poecile atricapillus, females pay attention not only to the intrinsic quality of male song but can also gather information, by eavesdropping on male–male singing interactions, on the relative quality of males. During these interactions, overlapping the song of the rival is more threatening than alternating. Moreover eavesdropping female canaries have been shown to prefer the overlapping song rather than the overlapped song. The present study was designed to assess the effect of the information gathered by eavesdropping on female investment in eggs. First, we broadcasted overlapping interactions to female canaries. Then, we broadcasted to each female one of the two songs previously heard and collected eggs. Females exposed to overlapping songs laid eggs with greater yolk ratio than females exposed to overlapped songs. In contrast, yolk testosterone quantity and concentration were not affected by the treatment. Moreover, we found a variation between eggs with regard to the testosterone deposited in yolk: both quantity and concentration increased with laying order. Our results suggest that female canaries use information gathered by eavesdropping to differentially allocate resources into the eggs. They suggest that singing interactions could influence chick quality via female investment.