Tissue- and development-specific distributions of cytoskeletal elements in growing cells of the maize root apex

ABSTRACT

Indirect immunofluorescence performed using sections of actively growing maize root apices fixed and then embedded in low-melting-point Steedman's wax has proved efficient in revealing the arrangements and reorganizations of motility-related cytoskeletal elements which are associated with root cell development and tissue differentiation. This powerful, yet relatively simple, technique shows that specific rearrangements of both microtubular (MT) and actin microfilament (MF) arrays occur in cells as they leave the meristem and traverse the transitional region interpolated between meristem and elongation region. Cytoskeletal and growth analyses have identified the transition zone as critical for both cell and root development; it is in this zone that cell growth is channelled, by the cytoskeleton, into a strictly polarized mode which enables root tips to extend rapidly through the soil in search of water and nutrients. An integrated cytoskeletal network is crucial for both the cytomorphogenesis of individual cells and the overall morphogenesis of the plant body. The latter process can be viewed as a reflection of the tight control which cytoskeletal networks exert not only over cell division planes in the cells within meristematic apices but also over the orientation of cell growth in the meristem and elsewhere. Endoplasmic MTs interconnecting the plasma membrane with the nucleus are suggested to be involved in cell division control; they may also act as a two-way cytoskeletal communication channel for signals passing to and fro between the extracellular environment and the genome. Moreover, the dynamism of endoplasmic MTs exerts direct effects on chromatin structure and the accompanying nuclear architecture and hence can help exert a cellular level of control over cell growth and cell cycle progression. Because the inherent dynamic instability of MTs depends on the concentration of tubulin dimers within the cytoplasm, we propose that when asymmetric cell division occurs, it will result in two daughter cells which differ in the turnover rates of their MTs. This phenomenon could be responsible for different cell fates of daughter plant cells produced by such cell divisions.     

Fluticasone impact on airway dendritic cells in smokers: a randomized controlled trial

Background

Myeloid Dendritic cells are key drivers of inflammation in smoke-related lung diseases, whereas plasmacytoid DCs play a crucial role in the defense against infections. Effects of inhaled corticosteroids (ICS) on airway DCs in smokers are unknown.

Methods

In this randomized, double-blind, placebo-controlled clinical trial, 45 active cigarette smokers inhaled placebo, fluticasone or fluticasone plus salmeterol twice daily for 4 weeks. Bronchoalveolar lavage fluid DCs were analyzed using four-color flow cytometry before and after the inhalation period. In addition, fluticasone effects were tested on T-cell proliferation in co-cultures with blood myeloid DCs from smokers.

Results

Inhalation of fluticasone plus salmeterol, but not fluticasone alone or placebo, reduced endobronchial concentrations of myeloid DCs (median decrease: 24%), macrophages (median decrease: 26%) and neutrophils (median decrease: 76%). In contrast, fluticasone reduced plasmacytoid DC concentrations independently of salmeterol. There were no changes in the expression of function-associated surface molecules on myeloid DC (such as CD1a, Langerin, BDCA-1, CD83 or CCR5) in all groups after treatment. Fluticasone (either alone or in combination with salmeterol) suppressed T-cell proliferation in co-cultures with blood myeloid DCs from smokers.

Conclusions

Resistance to ICS monotherapy in smokers might in part be due to lacking effects on airway myeloid DCs, whereas the increased risk for infections during ICS therapy could be attributable to a reduction in plasmacytoid DCs. Combination therapy of fluticasone with salmeterol is associated with a reduction in airway myeloid DCs, but also airway macrophages and neutrophils.

Trial registration

Registered at ClinicalTrials.gov (identifier: {"type":"clinical-trial","attrs":{"text":"NCT00908362","term_id":"NCT00908362"}}NCT00908362) and the European Clinical Trial Database, EudraCT (identifier: 2009-009459-40).     

Scl binds to primed enhancers in mesoderm to regulate hematopoietic and cardiac fate divergence

Scl/Tal1 confers hemogenic competence and prevents ectopic cardiomyogenesis in embryonic endothelium by unknown mechanisms. We discovered that Scl binds to hematopoietic and cardiac enhancers that become epigenetically primed in multipotent cardiovascular mesoderm, to regulate the divergence of hematopoietic and cardiac lineages. Scl does not act as a pioneer factor but rather exploits a pre‐established epigenetic landscape. As the blood lineage emerges, Scl binding and active epigenetic modifications are sustained in hematopoietic enhancers, whereas cardiac enhancers are decommissioned by removal of active epigenetic marks. Our data suggest that, rather than recruiting corepressors to enhancers, Scl prevents ectopic cardiogenesis by occupying enhancers that cardiac factors, such as Gata4 and Hand1, use for gene activation. Although hematopoietic Gata factors bind with Scl to both activated and repressed genes, they are dispensable for cardiac repression, but necessary for activating genes that enable hematopoietic stem/progenitor cell development. These results suggest that a unique subset of enhancers in lineage‐specific genes that are accessible for regulators of opposing fates during the time of the fate decision provide a platform where the divergence of mutually exclusive fates is orchestrated.     

Genetic differentiation,hybridization and adaptive divergence in two subspecies of the acorn barnacle Tetraclita japonica in the northwestern Pacific

Two acorn barnacles, Tetraclita japonica japonica and Tetraclita japonica formosana, have been recently reclassified as two subspecies, because they are morphologically similar and genetically indistinguishable in mitochondrial DNA sequences. The two barnacles are distinguishable by parietes colour and exhibit parapatric distributions, coexisting in Japan, where T. j. formosana is very low in abundance. Here we investigated the genetic differentiation between the subspecies using 209 polymorphic amplified fragment length polymorphism markers and 341 individuals from 12 locations. The subspecies are genetically highly differentiated (Φ_CT = 0.267). Bayesian analysis and principal component analysis indicate the presence of hybrids in T. j. formosana samples from Japan. Strong differentiation between the northern and southern populations of T. j. japonica was revealed, and a break between Taiwan and Okinawa was also found in T. j. formosana. The differentiation between the two taxa at individual loci does not deviate from neutral expectation, suggesting that the oceanographic pattern which restricts larval dispersal is a more important factor than divergent selection in maintaining genetic and phenotypic differentiation. The T. j. formosana in Japan are probably recent migrants from Okinawa, and their presence in Japan may represent a poleward range shift driven by global warming. This promotes hybridization and might lead to a breakdown of the boundary between the subspecies. However, both local adaptation and larval dispersal are crucial in determining the population structure within each subspecies. Our study provides new insights into the interplay of local adaptation and dispersal in determining the distribution and genetic structure of intertidal biota and the biogeography of the northwestern Pacific.     

A new late Westphalian fossil marattialean fern from Nova Scotia

Sydneia manleyi gen. et sp. nov. is based on part of a fertile frond from the upper Westphalian D of the Sydney Coalfield, Nova Scotia, Canada. It has small synangia composed of laterally fused sporangia that are elongate and with a circular cross-section. The sporangia yielded variably sized monolete and trilete spores with laevigate and microspinate ornamentation; intermediate forms were also observed. The spores can be correlated with the sporae dispersae species Latosporites minutus , Punctatosporites oculus and Laevigatosporites minimus . Size distribution of the spores is variable and highly skewed, suggesting heterogeneity of the spores within the sporangium. Spore ultrastructure indicates that the fossil is part of a fern, and the morphology of the spores and synangia indicate marattialean affinities.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 142 , 199–212.     

Host-associated speciation in the coral barnacle Wanella milleporae (Cirripedia: Pyrgomatidae) inhabiting the Millepora coral

Speciation by host shift is a common phenomenon observed in many symbiotic animals. The symbiont–host interaction is highly dynamic, but it is poorly documented in the marine realm. In the present study, we examined the genetic and morphological differentiation of the coral barnacle Wanella milleporae (obligate to fire corals) collected from four different Millepora host species in Taiwan to investigate the host specificity of this barnacle. Phylogenetic analysis of mitochondrial COI gene for 241 individuals of Wanella revealed five distinct clades, whose sequence divergences are comparable to values between other cogeneric barnacle species. The five clades also differ in shell and opercular plate morphology and colour. Genetic and morphological differentiations together strongly suggest the presence of cryptic species. Although the five clades do not display species-level host specificity, they showed a significant difference in preference on host growth form. Clades 1 and 2 were predominantly found on encrusting Millepora exaesa and Millepora platyphylla , while clades 3, 4 and 5 live exclusively on branching-form fire corals Millepora dichotoma and Millepora tenella . Phylogeny inferred from the combined mitochondrial COI, 16S and 12S (2182 bp) analysis suggests the division of the five clades into two major lineages congruent with the morphology of the host coral. Multiple independent invasions to the same form of host and subsequent speciation are evident in the Red Sea and Taiwan. Our results indicate that ecological/sympatric speciation could occur in marine symbiotic invertebrates through host shift and specialization. It appears that, as in their terrestrial counterparts, host–symbiont radiations in the marine realm are more prevalent than we expected and thus warrant further investigation.     

Disentangling genetic and epigenetic determinants of ultrafast adaptation

A major rationale for the advocacy of epigenetically mediated adaptive responses is that they facilitate faster adaptation to environmental challenges. This motivated us to develop a theoretical–experimental framework for disclosing the presence of such adaptation‐speeding mechanisms in an experimental evolution setting circumventing the need for pursuing costly mutation–accumulation experiments. To this end, we exposed clonal populations of budding yeast to a whole range of stressors. By growth phenotyping, we found that almost complete adaptation to arsenic emerged after a few mitotic cell divisions without involving any phenotypic plasticity. Causative mutations were identified by deep sequencing of the arsenic‐adapted populations and reconstructed for validation. Mutation effects on growth phenotypes, and the associated mutational target sizes were quantified and embedded in data‐driven individual‐based evolutionary population models. We found that the experimentally observed homogeneity of adaptation speed and heterogeneity of molecular solutions could only be accounted for if the mutation rate had been near estimates of the basal mutation rate. The ultrafast adaptation could be fully explained by extensive positive pleiotropy such that all beneficial mutations dramatically enhanced multiple fitness components in concert. As our approach can be exploited across a range of model organisms exposed to a variety of environmental challenges, it may be used for determining the importance of epigenetic adaptation‐speeding mechanisms in general.     

Impact of smoking on dendritic cell phenotypes in the airway lumen of patients with COPD

Background

Myeloid dendritic cells (DCs) are increased in the airway wall of patients with chronic obstructive pulmonary disease (COPD), and postulated to play a crucial role in COPD. However, DC phenotypes in COPD are poorly understood.

Methods

Function-associated surface molecules on bronchoalveolar lavage fluid (BALF) DCs were analyzed using flow cytometry in current smokers with COPD, in former smokers with COPD and in never-smoking controls.

Results

Myeloid DCs of current smokers with COPD displayed a significantly increased expression of receptors for antigen recognition such as BDCA-1 or Langerin, as compared with never-smoking controls. In contrast, former smokers with COPD displayed a significantly decreased expression of these receptors, as compared with never-smoking controls. A significantly reduced expression of the maturation marker CD83 on myeloid DCs was found in current smokers with COPD, but not in former smokers with COPD. The chemokine receptor CCR5 on myeloid DCs, which is also important for the uptake and procession of microbial antigens, was strongly reduced in all patients with COPD, independently of the smoking status.

Conclusion

COPD is characterized by a strongly reduced CCR5 expression on myeloid DCs in the airway lumen, which might hamper DC interactions with microbial antigens. Further studies are needed to better understand the role of CCR5 in the pathophysiology and microbiology of COPD.     

The biogeochemistry of basic cations in two forest catchments with contrasting lithology in the Czech Republic

The biogeochemistry of Ca, Mg, K, and Nawere investigated in two forested catchments in theCzech Republic, one underlain by leucogranite, theother by serpentinite. High weathering rates at theserpentinite site at Pluhv Bor resultedin Mg²⁺ as the dominant cation on the soilexchange complex and in drainage water. Other basiccations (Ca²⁺, K⁺, Na⁺) showedrelatively low concentrations and outflow instreamwater. The catchment exhibited high basesaturation in mineral soils (>70%), and nearneutral soil and stream pH, despite elevated inputsof acidic deposition. Slow growth of Norway spruceat Pluhv Bor may be caused by K deficiency, Mgoversupply and/or Ni toxicity. In contrast, thegranitic site at Lysina showed low concentrations ofbasic cations on the soil exchange complex and instreamwater. Soil and drainage water at Lysina werehighly impacted by acidic deposition. Soil pH wasextremely acidic (<4.5) throughout the soilprofile, and the base saturation of the mineral soilwas very low (<5%). Supplies of basic cationsfrom atmospheric deposition and soil processes wereless than inputs of SO^2- ₄ on anequivalence basis, resulting in low pH and highconcentrations of total Al in drainage water. Needle yellowing in Norway spruce was possibly theresult of Mg deficiency at Lysina. Because of theirextremely different lithologies, these catchmentsserve as valuable end-members of ecosystemsensitivity to elevated levels of acidicdeposition.